CPSC 441 Review 1

CPSC 441 Review (W06)

Instructor Dr Anirban MahantiOffice ICT 745Email mahanticpscucalgarycaDate April 12 2006

Text BookldquoComputer Networking A Top Down Approach

Featuring the Internetrdquo 3rd edition Jim Kurose and Keith Ross Addison-Wesley 2005

CPSC 441 Review 2

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 3

Reference Models

OSI model 7-layer model application presentation session transport network data link and physical

TCPIP model 4-layers application transport Internet and Host-to-Network

Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models

CPSC 441 Review 4

Layers and Protocols

Layered network architecture hellip why Reduces design complexity

The purpose of a layer Layer-N peers converse with each other

using protocols each layer provides functionality to the a higher layer

Protocols A set of rules governing the format and

meaning of messages exchanges by peer entities within a layer

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 2

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 3

Reference Models

OSI model 7-layer model application presentation session transport network data link and physical

TCPIP model 4-layers application transport Internet and Host-to-Network

Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models

CPSC 441 Review 4

Layers and Protocols

Layered network architecture hellip why Reduces design complexity

The purpose of a layer Layer-N peers converse with each other

using protocols each layer provides functionality to the a higher layer

Protocols A set of rules governing the format and

meaning of messages exchanges by peer entities within a layer

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 3

Reference Models

OSI model 7-layer model application presentation session transport network data link and physical

TCPIP model 4-layers application transport Internet and Host-to-Network

Internet Protocol Stack ndash a hybrid of TCPIP and OSI reference models

CPSC 441 Review 4

Layers and Protocols

Layered network architecture hellip why Reduces design complexity

The purpose of a layer Layer-N peers converse with each other

using protocols each layer provides functionality to the a higher layer

Protocols A set of rules governing the format and

meaning of messages exchanges by peer entities within a layer

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 4

Layers and Protocols

Layered network architecture hellip why Reduces design complexity

The purpose of a layer Layer-N peers converse with each other

using protocols each layer provides functionality to the a higher layer

Protocols A set of rules governing the format and

meaning of messages exchanges by peer entities within a layer

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 5

Protocols Layers and PDUrsquos

Protocol Layer PDUHTTP FTP Application layer messageTCP UDP Transport layer segmentICMP IP Network layer datagramPPP Ethernet Data link layer frameIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 6

More on Layers and Protocols

Protocol Layer Imm Lower LayerHTTP FTP Application TransportTCP UDP Transport NetworkICMP IP Network Data LinkPPP Ethernet Data Link PhysicalIEEE 80211

Assuming the Internet Protocol Stack

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 7

Internetworks

A collection of interconnected networks is called an ldquointernetworkrdquo or an ldquointernetrdquo Internet is one example of a really big internetwork

Internet structure Tier-1 ISPs Tier-2 ISPs Tier-3 ISPs NAP POP etc

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 8

Network Core

Packet switching ndash a technique for transmission of packets that allows multiple end systems to share a ldquorouterdquo Virtual circuit vs datagram networks

Circuit switching ndash a technique that requires end-to-end resource reservation for a ldquocallrdquo TDMA FDMA

Circuit vs Message vs Packet Switching

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 9

DelayLoss in Packet Switched Networks

Queuing delay and packet loss

Transmission delay

Propagation delay

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 10

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 11

Application Layer

Processes communicating across networks

What is HTTP Hypertext Transfer Protocol ndash the Webrsquos

application layer protocol HTTP 10 HTTP 11 Pipelined ndash requests sent as soon as it is

encountered Persistent ndash multiple objects can be sent

over a single TCP connection between the server and the client

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 12

HTTP Continued hellip

HTTP headers How is the end of an object determined in

HTTP11 HTTP methods

GET HEAD POST PUT hellip HTTP response codes

1xx 2xx 3xx 4xx 5xx

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 13

The World Wide Web

What is a Web Proxy What is a caching hierarchy Caching issues ndash

Cache consistency issuesbull The ldquoconditional HTTP GETrdquo request

Cache replacement issues Prefetching

Cookies ndash a means to maintain state in stateless HTTP servers

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 14

DNS Domain Name System

Internet hosts IP address (32 bit) - used for addressing

datagrams ldquonamerdquo eg wwyahoocom - used by

humans

DNS provides translation between host name and IP address distributed database implemented in

hierarchy of many name servers Distributed for scalability amp reliability

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 15

DNS Services

Hostname to IP address translation Host aliasing

Canonical and alias names Mail server aliasing Load distribution

Replicated Web servers set of IP addresses for one canonical name

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 16

requesting hostcispolyedu

gaiacsumassedu

root DNS server

local DNS serverdnspolyedu

1

23

4

5

6

authoritative DNS serverdnscsumassedu

78

TLD DNS server

DNS Infrastructure

Host at cispolyedu wants IP address for gaiacsumassedu

Infrastructure Client resolver Local DNS server Authoritative DNS

Server Root DNS Server Top-Level Domain

DNS Server

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 17

Electronic Mail

Three major components

user agents eg Eudora Outlook

Pine Netscape Messenger

mail servers Incoming outgoing

messages Push protocol ndashSMTP

Pull protocol ndash HTTP IMAP POP3

user mailbox

outgoing message queue

mailserver

useragent

useragent

useragent

mailserver

useragent

useragent

mailserver

useragent

SMTP

SMTP

SMTP

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 18

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 19

Transport Layer

Logical end-to-end communication between processes running on different end systems

Multiplexingde-multiplexing Service models UDP vs TCP

UDP provides multiplexingde-multiplexing In addition to the above TCP provides flow

control congestion control and reliable data delivery

Some applications use UDP while some use TCP Why

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 20

Reliable Delivery Concepts

GBN SR ndash also called ldquostop-and-waitrdquo protocols

ACK NAK SACK Performance of ldquostop-and-waitrdquo

Pipelining Similaritydifferences between TCP and

the above protocols

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 21

TCP segment structure (12)

source port dest port

32 bits

applicationdata

(variable length)

sequence number

acknowledgement numberReceive window

Urg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 22

TCP Segment Structure (22)

Sequence and acknowledgement numbering

TTL Checksum ndash compulsory in TCP but not

in UDP Handshaking procedures during TCP

connection set-up and connection termination SYN FIN RST fields

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 23

TCP Flow Control

receive side of TCP connection has a receive buffer

speed-matching service matching the send rate to the receiving apprsquos drain rate app process may be

slow at reading from buffer

sender wonrsquot overflow

receiverrsquos buffer bytransmitting too

much too fast

flow control

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 24

TCP Connection Establishment

client

SYN seq=x

server

SYN+ACK seq=y ack=x+1

ACK ack=y+1

CLOSED

LISTEN

SYN_SENTSYN_RCVD

Established

Passive open

SYNSYN+ACK

ACK

Active openSYN

SYN+ACKACK

Solid line for client

Dashed line for server

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 25

TCP Connection Termination

client

FIN

server

ACK

ACK

FIN

closing

tim

ed w

ait

FIN_WAIT1

FIN_WAIT2

CLOSE_WAIT

LAST_ACK

CLOSED

TIME_WAIT

CLOSED

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 26

Principles of Congestion Control Congestion informally ldquotoo many sources

sending too much data too fast for network to handlerdquo

Different from flow control Manifestations

Packet loss (buffer overflow at routers) Increased end-to-end delays (queuing in router

buffers) Results in unfairness and poor utilization of

network resources Resources used by dropped packets (before they

were lost) Retransmissions Poor resource allocation at high load

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 27

Congestion Control Approaches Goal Throttle senders as needed to ensure

load on the network is ldquoreasonablerdquoEnd-end congestion control

no explicit feedback from network congestion inferred from end-system

observed loss delay approach taken by TCP

Network-assisted congestion control routers provide feedback to end systems single bit indicating congestion (eg ECN) explicit rate sender should send at

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 28

TCP Congestion Control Overview end-end control (no network assistance) Limit the number of packets in the

network to window W Roughly

W is dynamic function of perceived network congestion

rate = W

RTT Bytessec

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 29

TCP Congestion Controls Tahoe (Jacobson 1988)

Slow Start Congestion Avoidance Fast Retransmit

Reno (Jacobson 1990) Fast Recovery

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 30

TCP Tahoe Basic ideas

Gently probe network for spare capacity Drastically reduce rate on congestion Windowing self-clocking Other functions round trip time

estimation error recoveryfor every ACK

if (W lt ssthresh) then W++ (SS) else W += 1W (CA)

for every loss

ssthresh = W2 W = 1

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 31

TCP Reno Fast Recovery Objective prevent `pipersquo from emptying

after fast retransmit each dup ACK represents a packet having

left the pipe (successfully received) Letrsquos enter the ldquoFRFRrdquo mode on 3 dup ACKs

ssthresh W2retransmit lost packetW ssthresh + ndup (window inflation)Wait till W is large enough transmit new packet(s)On non-dup ACK (1 RTT later)

W ssthresh (window deflation)enter CA mode

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 32

TCP Reno Summary

Fast Recovery along with Fast Retransmit used to avoid slow start

On 3 duplicate ACKs Fast retransmit and fast recovery

On timeout Fast retransmit and slow start

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 33

TCP Reno Throughput Average throughout 75 WRTT Throughput in terms of loss rate

What happens if L-gt0 Does link capacity matter if we

experience random loss High-speed TCP

LRTT

MSS221

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 34

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 35

Network Layer

Transport segment from sending to receiving host

Network layer protocols in every host router [contrast with transportapplication layer]

Main functions of network layer Forwarding ndash moving datagrams within a

router Routing ndash determine end-to-end paths taken

by packets

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 36

IP datagram format

ver length

32 bits

data (variable lengthtypically a TCP

or UDP segment)

16-bit identifier

Internet checksum

time tolive

32 bit source IP address

IP protocol versionnumber

header length (bytes)

max numberremaining hops

(decremented at each router)

forfragmentationreassembly

total datagramlength (bytes)

upper layer protocolto deliver payload to

headlen

type ofservice

ldquotyperdquo of data flgsfragment

offsetupper layer

32 bit destination IP address

Options (if any) Eg timestamprecord routetaken specifylist of routers to visit

how much overhead with TCP

20 bytes of TCP 20 bytes of IP = 40 bytes + app

layer overhead

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 37

IPv4 Addressing IP address 32-bit

identifier for host router interface

interface connection between hostrouter and physical link routerrsquos typically have

multiple interfaces host may have

multiple interfaces IP addresses

associated with each interface

223111

223112

223113

223114 223129

223122

223121

223132223131

2231327

223111 = 11011111 00000001 00000001 00000001

223 1 11

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 38

Classful Addressing

Addresses consists of Network part Host part

IP addresses divided into five classes A B C D and E

Problems

0Network (7 bits)

Host (24 bits)

1 Network(14 bits)

Host (16bits)

0

1110 Multicast address

Class A

Class D

Class B

110 Network(21 bits)

Host (8bits)

Class C

1111 Future use addresses

Class E

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 39

Subnets Motivation

The ldquoclassfulrdquo addressing scheme proposes that the network portion of a IP address uniquely identifies one physical network Any network with more than 255 hosts

needs a class B address Class B addresses can get exhausted before we have 4 billion hosts

Take bits from the host number part to create a ldquosubnetrdquo number

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 40

Addressing in the Internet

CIDR Classless InterDomain Routing subnet portion of address of arbitrary length address format abcdx where x is bits in

subnet portion of address Before CIDR Internet used a class-based

addressing scheme where x could be 8 16 or 24 bits These corrsp to classes A B and C resp

11001000 00010111 00010000 00000000

subnetpart

hostpart

2002316023

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 41

NAT Network Address Translation

10001

10002

10003

10004

13876297

local network(eg home network)

100024

rest ofInternet

Datagrams with source or destination in this networkhave 100024 address for

source destination (as usual)

All datagrams leaving localnetwork have same single source

NAT IP address 13876297different source port numbers

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 42

Routing Algorithm Classification

1 Global decentralized

Global all routers have complete

topology link cost info ldquolink staterdquo algorithmsDecentralized router knows about

physically-connected neighbors

Iterative distributed computations

ldquodistance vectorrdquo algorithms

2 Static dynamicStatic routes change slowly

over time

Dynamic routes change more

quickly periodic update in response to link

cost changes

3 Load sensitivity Many Internet routing

algos are load insensitive

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 43

Why Hierarchical Routing scale with 200 million destinations

canrsquot store all destrsquos in routing tables routing table exchange would swamp links

administrative autonomy internet = network of networks each network admin may want to control routing in

its own network

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 44

Hierarchical Routing

aggregate routers into regions ldquoautonomous systemsrdquo (AS)

routers in same AS run same routing protocol ldquointra-ASrdquo routing

protocol routers in different AS

can run different intra-AS routing protocol

Gateway router Direct link to router

in another AS Establishes a

ldquopeeringrdquo relationship

Peers run an ldquointer-AS routingrdquo protocol

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 45

3b

1d

3a

1c2aAS3

AS1

AS21a

2c2b

1b

Intra-ASRouting algorithm

Inter-ASRouting algorithm

Forwardingtable

3c

Interconnected ASes

Forwarding table is configured by both intra- and inter-AS routing algorithm Intra-AS sets entries

for internal dests Inter-AS amp Intra-As

sets entries for external dests

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 46

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 47

Link Layer IntroductionSome terminology hosts and routers are nodes communication channels

that connect adjacent nodes along communication path are links wired links wireless links LANs

layer-2 packet is a frame encapsulates datagram

ldquolinkrdquo

data-link layer has responsibility of transferring datagram from one node to adjacent node over a link

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 48

ARP Address Resolution Protocol

Each IP node (Host Router) on LAN has ARP table

ARP Table IPMAC address mappings for some LAN nodes

lt IP address MAC address TTLgt

TTL (Time To Live) time after which address mapping will be forgotten (typically 20 min)

Question how to determineMAC address of Bknowing Brsquos IP address

1A-2F-BB-76-09-AD

58-23-D7-FA-20-B0

0C-C4-11-6F-E3-98

71-65-F7-2B-08-53

LAN

237196723

237196778

237196714

237196788

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 49

Multiple Access Links and Protocols

Two types of ldquolinksrdquo point-to-point

PPP for dial-up access point-to-point link between Ethernet switch and host

broadcast (shared wire or medium) traditional Ethernet upstream HFC 80211 wireless LAN

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 50

Taxonomy of Multiple Access Control Protocols

Three broad classes Channel Partitioning

divide channel into smaller ldquopiecesrdquo (TDM FDM Code Division Multiple Access)

allocate piece to node for exclusive use Random Access

channel not divided allow collisions ldquorecoverrdquo from collisions

ldquoTaking turnsrdquo Nodes take turns but nodes with more to

send can take longer turns

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 51

Random Access Protocols

When node has packet to send transmit at full channel data rate R no a priori coordination among nodes

two or more transmitting nodes ldquocollisionrdquo random access MAC protocol specifies

how to detect collisions how to recover from collisions (eg via delayed

retransmissions)

Examples of random access MAC protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 52

CSMACD (Collision Detection)CSMACD carrier sensing deferral as in

CSMA collisions detected within short time colliding transmissions aborted reducing

channel wastage collision detection

easy in wired LANs measure signal strengths compare transmitted received signals

difficult in wireless LANs receiver shut off while transmitting

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 53

Ethernet CSMACD algorithm

1 Adaptor receives datagram from net layer amp creates frame

2 If adapter senses channel idle it starts to transmit frame If it senses channel busy waits until channel idle and then transmits

3 If adapter transmits entire frame without detecting another transmission the adapter is done with frame

4 If adapter detects another transmission while transmitting aborts and sends jam signal

5 After aborting adapter enters exponential backoff after the mth collision adapter chooses a K at random from 012hellip2m-1 Adapter waits K512 bit times and returns to Step 2

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 54

Ethernetrsquos CSMACD (more)

Jam Signal make sure all other transmitters are aware of collision 48 bits

Bit time 1 microsec for 10 Mbps Ethernet for K=1023 wait time is about 50 msec

Exponential Backoff Goal adapt retransmission

attempts to estimated current load heavy load random wait

will be longer first collision choose K

from 01 delay is K 512 bit transmission times

after second collision choose K from 0123hellip

after ten collisions choose K from 01234hellip1023

Seeinteract with Javaapplet on AWL Web sitehighly recommended

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 55

CSMACD efficiency tprop = max prop between 2 nodes in LAN

ttrans = time to transmit max-size frame

Efficiency goes to 1 as tprop goes to 0

Goes to 1 as ttrans goes to infinity Much better than ALOHA but still decentralized simple and cheap

transprop tt 51

1efficiency

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 56

Switches Routers and Hubs Hubs are physical layer repeaters

no CSMACD at hub

Switch is a link layer store-and-forward device CSMACD at switch Maintains switch tables implement filtering learning

algos

Routers are network-layer store-and-forward devices maintain routing tables implement routing algorithms

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 57

A network with switch router and hubs

hub

hubhub

switch

to externalnetwork

router

IP subnet

mail server

web server

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 58

Wireless Networking Technologies Mobile devices ndash laptop PDA cellular

phone wearable computer hellip

Operating modes Infrastructure mode (Access Point) Ad hoc mode

Access technology Bluetooth (1 Mbps up to 3 meters) IEEE 80211 (up to 55 Mbps 20 ndash 100

meters)

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 59

Infrastructure Mode

network infrastructure

infrastructure mode base station

connects mobiles into wired network

handoff mobile changes base station providing connection into wired network

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 60

Ad hoc Mode

Ad hoc mode no base stations nodes can only

transmit to other nodes within link coverage

nodes organize themselves into a network route among themselves

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 61

Wireless Network CharacteristicsMultiple wireless senders and receivers create

additional problems (beyond multiple access)

AB

C

Hidden terminal problem B A hear each other B C hear each other A C can not hear each

othermeans A C unaware of their

interference at B

A B C

Arsquos signalstrength

space

Crsquos signalstrength

Signal fading B A hear each other B C hear each other A C can not hear each other

interfering at B

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 62

IEEE 80211 MAC Protocol CSMACA

80211 sender1 if sense channel idle for DIFS then

transmit entire frame (no CD)2 if sense channel busy then

start random backoff timetimer counts down while channel idletransmit when timer expires

3 if no ACK increase random backoff interval repeat 2

80211 receiver- if frame received OK

return ACK after SIFS (ACK needed due to hidden terminal problem)

sender receiver

DIFS

data

SIFS

ACK

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 63

Avoiding collisions (more)

idea allow sender to ldquoreserverdquo channel rather than random access of data frames avoid collisions of long data frames

sender first transmits small request-to-send (RTS) packets to base station using CSMA RTSs may still collide with each other (but theyrsquore

short) BS broadcasts clear-to-send CTS in response to RTS RTS heard by all nodes

sender transmits data frame other stations defer transmissions

Avoid data frame collisions completely using small reservation packets

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 64

Collision Avoidance RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 65

Mobile IP Overview

Let routing handle it routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange routing tables indicate where each mobile

located no changes to end-systems

let end-systems handle it indirect routing communication from

correspondent to mobile goes through home agent then forwarded to remote

direct routing correspondent gets foreign address of mobile sends directly to mobile

not scalable

to millions of mobiles

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 66

Outline Introduction

Applications

Transport Layer

Network Layer

LANs and WLANs

Multimedia Networking

Questions

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 67

MM Networking Applications Fundamental

characteristics Typically delay

sensitive end-to-end delay delay jitter

But loss tolerant infrequent losses cause minor glitches

Antithesis of data

Classes of MM applications

1) Streaming stored audio and video

2) Streaming live audio and video

3) Real-time interactive audio and videoJitter is the variability of packet delays within the same packet stream

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 68

Multimedia Over ldquoBest Effortrdquo InternetTCPUDPIP no guarantees on delay

loss

Todayrsquos multimedia applications implement functionality at the app layer to mitigate

(as best possible) effects of delay loss

But you said multimedia apps requiresQoS and level of performance to be

effective

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 69

How to provide better support for Multimedia (14)

Integrated services philosophy architecture for providing QOS guarantees in IP networks for individual flows

Fundamental changes in Internet so that apps can reserve end-to-end bandwidth

Components of this architecture are Admission control Reservation protocol Routing protocol Classifier and route selection Packet scheduler

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 70

Concerns with Intserv (24) Scalability signaling maintaining per-flow router state difficult with

large number of flows Flexible Service Models Intserv has only two classes Desire

ldquoqualitativerdquo service classes Eg Courier xPress and normal mail Eg First business and cattle class

Diffserv approach simple functions in network core relatively complex functions at

edge routers (or hosts) Donrsquot define define service classes provide functional components

to build service classes

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 71

How to provide better support for Multimedia (34) Challenging to stream large

files (eg video) from single origin server in real time

Solution replicate content at hundreds of servers throughout Internet content downloaded to

CDN servers ahead of time

placing content ldquocloserdquo to user avoids impairments (loss delay) of sending content over long paths

CDN server typically in edgeaccess network

origin server in North America

CDN distribution node

CDN serverin S America CDN server

in Europe

CDN serverin Asia

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 72

How to provide better support for Multimedia (44)

R1

R2

R3 R4

(a)

R1

R2

R3 R4

(b)

duplicatecreationtransmissionduplicate

duplicate

Source-duplication versus in-network duplication (a) source duplication (b) in-network duplication

MulticastBroadcast

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 73

Finally hellip Examination Format Technical Terms ndash provide technical

terms that best fit a given definition Eg A field in IPv4 that provides for error

detection ndash Checksum Some short answer questions

Eg Compare and contrast datagram networks and virtual circuit networks

You need to only write main points Answer should be as brief as possible

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip

CPSC 441 Review 74

Good Luck and Questions hellip

• CPSC 441 Review (W06)
• Outline
• Reference Models
• Layers and Protocols
• Protocols Layers and PDUrsquos
• More on Layers and Protocols
• Internetworks
• Network Core
• DelayLoss in Packet Switched Networks
• Slide 10
• Application Layer
• HTTP Continued hellip
• The World Wide Web
• DNS Domain Name System
• DNS Services
• DNS Infrastructure
• Electronic Mail
• Slide 18
• Transport Layer
• Reliable Delivery Concepts
• TCP segment structure (12)
• TCP Segment Structure (22)
• TCP Flow Control
• TCP Connection Establishment
• TCP Connection Termination
• Principles of Congestion Control
• Congestion Control Approaches
• TCP Congestion Control Overview
• TCP Congestion Controls
• TCP Tahoe
• TCP Reno Fast Recovery
• TCP Reno Summary
• TCP Reno Throughput
• Slide 34
• Network Layer
• IP datagram format
• IPv4 Addressing
• Classful Addressing
• Subnets Motivation
• Addressing in the Internet
• NAT Network Address Translation
• Routing Algorithm Classification
• Why Hierarchical Routing
• Hierarchical Routing
• Interconnected ASes
• Slide 46
• Link Layer Introduction
• ARP Address Resolution Protocol
• Multiple Access Links and Protocols
• Taxonomy of Multiple Access Control Protocols
• Random Access Protocols
• CSMACD (Collision Detection)
• Ethernet CSMACD algorithm
• Ethernetrsquos CSMACD (more)
• CSMACD efficiency
• Switches Routers and Hubs
• A network with switch router and hubs
• Wireless Networking Technologies
• Infrastructure Mode
• Ad hoc Mode
• Wireless Network Characteristics
• IEEE 80211 MAC Protocol CSMACA
• Avoiding collisions (more)
• Collision Avoidance RTS-CTS exchange
• Mobile IP Overview
• Slide 66
• MM Networking Applications
• Multimedia Over ldquoBest Effortrdquo Internet
• How to provide better support for Multimedia (14)
• Concerns with Intserv (24)
• How to provide better support for Multimedia (34)
• How to provide better support for Multimedia (44)
• Finally hellip Examination Format
• Good Luck and Questions hellip