Overview 1 Overview 2Goal of Computer communications

via

communication networks

(physical communication)

ClientSRC/DEST

ServerDEST/SRC

Rea

l dat

aflo

wReal data flow

(logical communication)

cloud

Since 1970’s . . .

Computernetworks

(to hide the complexity)

Model of Computer CommunicationsModel of Computer Communications

Overview 3

The Goal of Communication

Information Exchangeand

Resource sharing

Since the old time . . .

and now getting . . .

much more Sharing, Interaction , and Fun.

Overview 4

The Four Era of NetworkingThe Four Era of Networking

• Era 1: Mainframe Networks (1965-1975)

– IBM 360/370 + control units + terminals

– Telephone line bandwidth, taking turns

• Era 2: Minicomputer Networks (1975-1985)

– DEC PDP-11/70 VAX + Data PBX + Terminals

– 10Mbps Ethernet + T1 (Muxtiplexed)

• Era 3: Shared-Bandwidth LANs (1985-1995)

– Ethernet bus/hub + routers

• Era 4: Switched Networks (1995 2005 ? )

– LAN switches + ATM switches + routers

Overview 5

Network Structure – A Closer LookNetwork Structure – A Closer Look

• Communication linksi.e., Physical media(selective discussion later)

• Network core:

– Switches/Routers,network of networks

– Switching techniques

• Network edge:- applications and hosts

(end systems)- CO/CL services

(continue . . .)

wireless

AP

• so-called“backbone”

( ( ))

So…• Access networks

Overview 6

NetworkNetwork CoreCore

• Mesh ( )of interconnected routers (mostly) or switches

• The fundamental question:

How do data be transferredHow do data be transferredthrough network(s)?through network(s)?

– Circuit-switching: dedicated

circuit/path per call(?), e.g.,

telephone network (Plain Old

Telephone Service)

– Packet-switching:

data sent through net in discrete “chunks”

AP

Overview 7

NetworkNetwork EdgeEdge• End systems (hosts):

– run application programs– e.g., WWW, email– at “edge of network”

•• Client/serverClient/server model (CS):– client host requests, receives

service from server– e.g., WWW client (browser)/ server;

email client/server•• PeerPeer--toto--peerpeer model (P2P):

– host interaction symmetric– Since Napster, 1999– e.g., (video) teleconferencing,

file-sharing (New Internet DirectoryService) eDonkey, eMule, Gnutella, KaZaA, ezPeer, Kuro

• Edge device(named w.r.t. core device)

AP

Overview 8

AccessAccess NetworksNetworks

Q: How to connect end systems to edge router?

• residential access nets• institutional access

networks (school, company)

• mobile access networks

(click to see the details)

AP

• Keep in mind: the connection- bandwidth (bits per second) ?

(media-dependent)- shared or dedicated ?

(topology-dependent)

Overview 9

Residential Access - I: point to point access

• Dialup via modem

- up to 56Kbps direct access to router (conceptually)

• ISDN:

- Integrated Services Digital Network

- BRI - 64x2+16, PRI - 1544 Kbps all-digital connect to router

• xDSL: digital subscriber line

(e.g., Asymmetric ADSL)

– up to 1 Mbps home-to-router

– up to 8 Mbps router-to-home(Speed is continuously enhancing.)

dedicated

Subscriber’sLocal loop(last mile)

Overview 10

ADSL(Asymmetric Digital Subscriber Loop ) Networking

SplitterATUATU--RR

Filter

ATUATU--RR

Filter

ATUATU--RR

Filter

.

.

.

Hinet ISP

DSLAMDSLAM62006200

ATM

Data STM-1 STM-1

TANET

ATMATM

,

PSTN

POTS

POTS: 0 ~ 4KHzUplink: 25 ~ 170KHzDownlink: 200KHz ~ 1.1MHz

POTS

,

1.1MHz

Ex: : 64Kbps - 6Mbps; : 1.5Mbps - 4.1 w/ 26AWG

: 64Kbps – 640Kbps (( ))

Overview 11

xDSL Modem Technology

DSL Service Max. Data Rate

Down/Uplink

(bps)

Copper

Pairs

Required

Analog

Voice

Support

Max. Reach

(km - feet)

VDSL - Very high bit-rate

DSL

25M/1.6M

or 8M/8M

1 Yes .9 - 3,000

ADSL - Asymmetric DSL 7M/1M 1 Yes 5.5 - 18,000

HDSL - High bit rate DSL 1.5M - 2.0M/

1.5M - 2.0M

2 No 4.6 - 15,000

SDSL - Symmetric DSL 784K/784K 1 No 6.9 - 22,000

IDSL - ISDN DSL 144K/144K 1 No 5.5 - 18,000

ISDN 128K/128K 1 No 5.5 - 18,000

PSTN ~ Public Switch Telephone NetworksPOTS ~ Plain Old Telephone Services

Overview 12

Residential Access - II: Cable Modems

• HFC: Hybrid Fiber Coax (network)– asymmetric: up to 10Mbps upstream, 1 Mbps downstream

(by FDM)– Network of cable and fiber attaches homes to ISP router– shared access to links among homes– Deployment: available via cable companies

ONU ~ optical networking unit; SO ~ switching office

SO

SO

SOSOHeadendHeadend

shared

Overview 13

Cable Network Architecture: OverviewCable Network Architecture: Overview

cable distributionnetwork (simplified)

(500~5000 homes)

server(s)

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

Ref: http://www.cabledatacomnews.com/cmic/diagram.html

cable headend

home

Overview 14

Institutional Access: Local Area NetworksInstitutional Access: Local Area Networks• Company/university’s local

area network (LAN) connects end systems to edge router

• Ethernet: (a popular example)

– shared or dedicated cableconnects end system(s) and router(s), with somethingelse in between

– 10 Mbs, 100Mbps, Gigabit Ethernet

• Deployment: institutions, homeLANs (soon)

• LANs: (discussed later)

Port/interface

Shared/dedicated

Overview 15

Mobile Access NetworksMobile Access Networks

• Shared wireless access networkconnects end systems to router

• Wireless LANs: (hot spot)– radio spectrum replaces wire– e.g., Lucent Wavelan 10Mbps

• Wider-area wireless access– CDPD: wireless access to ISP

router via cellular network(Cellular Digital Packet Data)over Advance Mobile Phone (AMP) Service

- SM/MMS/EMS/WAP over GSM/GPRS/3G (WirelessApplication Protocol, General Packet Radio Service) overMobile phone

basestation

mobilehosts

router

AP ~ access point

AP

shared

Overview 16

Communication LinksCommunication Links -- MediaMedia

• Transmission media

~ physical path (wired or wireless) between transmitter

and receiver

(Propagation is in the form of electromagnetic (EM) waves.)

• Media

GuidedGuided media ~ media ~ waves are guided along a physical path

Twisted pair, Coaxial cable, Optical fiber

UnguidedUnguided media ~ media ~ offering a means of transmittingEM waves but do not guide them

Radio, Laser, Infrared, Microwave

Overview 17

Signals TerminologySignals Terminology Related to T.M.

• Information ~ an abstract object

Message ~ a concrete form of information

Data ~ an entity that convey meaning

Signal ~ an electric or an electromagnetic

encoding of data for being transmitted

Transmission ~ the communication of data by the

propagation and processing of signals

• Analog continuous

Digital discrete Data, signal, Transmissionvs

value/amplitude vs time scaleOverview 18

• Analog data ~ take on continuous (real number) values

on some interval (e.g., voice and video)

Digital data ~ take on discrete values

(e.g., text and integers/numbers in Telegraph)

• Analog signal

~ represent data with continuously varying voltage or

electromagnetic wave

Digital signal

~ represent data with sequence of voltage/current/light pulses

Overview 19

Signal, Harmonics, and Spectra

))1052sin((

))1032sin(())102sin((4)(

651

6316

t

ttts

(Line) spectra

Overview 20

BandwidthBandwidth andand Data RateData Rate

• Harmonic and Signal bandwidth

Harmonics byFourier analysis

(one cycle)

• # of harmonics better approximation of signals(composite of harmonics)

Overview 21

• Data rate ~ the rate/speed in bit per sec (bps) at which

data can be communicated

• Bandwidth ~ frequency range/width of a signal or

a system (e.g., for a transmission medium)

- Max # of times /sec the signal can change (baud rate)

• Relation between data rate and bandwidth

– Data rate = R bps, Time for sending 8-bit = T = 8 (1/R)

then, the first harmonic (fundamental) freq. = 1/T = R/8

– Consider a voice-grade channel with BW = 3000 Hz

No of harmonics (can be sent) = 3000/(R/8) = 24000/R

(or the system allows it to change)

i.e., getting through the channelOverview 22

Data Rate vs Harmonics

limited (system) BW limiting maximum data rate

(due to larger distortion)Channel capacity

,R

Any transmission system/media has a limited band offrequencies (i.e., the system bandwidth)

This limits the data rate that can be carried

Overview 23

MediaMedia –– Twisted PairsTwisted Pairs

Shielded TP (STP)Unshielded TP (UTP)

• Twisted Pair

Help reduce interference

- Copper wire, 24AWG (Diameter = 0.5mm)- used in telephone and intrabuilding LAN connection

- USA : Category 1 (1MHz) ~ Cat. 5 (100MHz)

- UL (Underwriting Laboratories, Inc) :

Level 1 ~ Level 5

- IEEE EIA 568-A/B (=AT&T 258A) : Wiring standard for LAN

- Ex: AT&T Power Sum Enhance Cat. 5

UTP

RJ-45

8.1

Overview 24

UTP ClassificationsUTP Classifications

Category 1 2Mbps Voice application

Category 2 4Mbps voice 4Mbps token ring

Category 3 16Mbps 100BaseT 16Mbps token ring

Category 4 20Mbps 100BaseT4 16Mbps token ring

Category 5 100Mbps 100BaseTX

Category 5E 1000Mbps 1000BaseT

Category 6 2.4Gbps 1000BaseT

E ~ enhanced NEXT = 1/4 of Cat5’s; Power sum NEXT = 1/8 of Cat. 5’s

• Some notations marked on UTP jacket: (Defined by Article 800, National Electric Codes)CM (Communication): Horizontal cabling, e.g., room to roomCMR (Communication Riser): Vertical cabling, e.g., floor to floorCMP (Communication Plenum ): Horizontal and vertical cabling

Overview 25

AttenuationAttenuation~ the amount of signal loss in a transmission link/media

• Examples:

1/1 0 dB1/2 - 6 dB 1/10 - 20 dB

lossvrec/vsrc

src

rec

v

vlossdB 10log20

• Measurement

Signalsource

Signalreception

dB loss

Just sending Receiving atFar-end

vrecvsrc

Overview 26

NEXT

• Near-End CrossTalk (NEXT)

the coupling of the signal from one

pair of conductors to another pair

the near-transmitted signal is picked up

by the near-receiver pair

- The biggest noise in twisted-pair wiring system

NEXT = 10*log10(Pinterfering / Pcrosstalk_in_interfered_end)

(NEXT measured in dB; The higher, the better.)

TX

RX

measured at the RX-end

• In addition, FARNEXT (FEXT) and Power Sum NEXT

Overview 27

Comparisons of UTP and STP

Overview 28

EIA/TIA 568A/B 8P8C Pin AssignmentEIA/TIA 568A EIA/TIA 568B, AT&T 258A

1

8

RJ-45

P ~ positionC ~ contact

Tx-Rx-6

Tx+Rx+3

Rx-Tx-2

Rx+Tx+1

HubNICPin #

Overview 29

• PC – Hub : use straight cable

•

Interconnection for PCs (Hubs)(review)

(pin)RJ-45 RJ-45

1 (Tx+) (Rx+)

2 (Tx-) (Rx-)

3 (Rx+) (Tx+)

4

5

6 (Rx-) (Tx-)

7

8

• PC – PC or Hub – Hub :

~ use crossover cable

Overview 30

(review)

MediaMedia –– Coaxial CableCoaxial Cable

- shielded, concentric construction much lesssusceptible to interference and cross talk (than in TP)

- used over longer distance and support multiple-stationconnections (multidrop); Ex: bus network - 10Base2

Cross-section view

(outer)

(protective)

RG-58 cableBNC type

• Coaxial Cable structure

Overview 31

(review)

MediaMedia –– Fiber opticsFiber optics

- Use optical instead of electrical signaling(free from interference)(Transmitting light sources : laser Diode or LED) (Detection light-pulse : photoelectric diodes)

- Light transmission dep. on “propagation mode” & “index profile”- Operating frequency: 1014 Hz ~ 1015 Hz

Straight-Connected Straight-Twisted Overview 32

• Best wavelength “windows” for light propagation in FO:centered on 850, 1300, and 1550 nm (infrared frequency)

Wavelength ~ 200 um, BW ~ 30 THz (1012)

• Wavelength window ~ 200nm max.- Attenuation of light through the fiber in the infrared region

Overview 33

Refraction and Reflection at the Boundary

n1sin = n2sin~

• Snell’s law :

Refraction

Absorbedby claddingor jactet

• Total internal Reflection( needs: n1 > n2 )

v

cnindexRefraction

n = 1.0 for air,

1.5 for glass

normal

(more dense)

(less dense)

Overview 34

(review)Two FO Transmission Modes

• Single-mode (SMF)- core diameter (1.5~10um) < wavelength one transmission path- used for longer distance (Ex: 2 Gbps over 30 km)

Inner core

Light ray out

Light ray in

claddingMode = path

(propagates light ray by refraction)

• Multimode (MMF)- multiple reflection angles of ray internally (various modes/paths)- signal element spreading out limits the distance & speed

Direct rayHigher-Order

mode Inner coreCladding (jacket)

air

squeeze

Overview 35

(review)

Different Index Profiles

Step-indexSMF

n

Graded-indexMMF

n

Step-indexMMF

air

n

large

Overview 36

Focusing Effect of Different ModesFocusing Effect of Different Modes(review)

Axial ray

( with higher refraction index at center)

(different modes take different times to traval)

timedispersion

Overview 37

(review)

Some comments on FO

Graded-index MMF – with good focusing effect~ Because the refractive index decreases with

distance from the center and the velocity is Inversely proportional to the refraction index.

The propagation speed of light inside a FO is NOT as fast as light speed in vacuum. How fast is it ?

~ 194,865 km/sec in glass or optic fiber

( vs 224,844 km/sec in copper)

The factor limiting the use of FO is not the cost of FO itself but the cost of installation.

Overview 38

(review)

Comparisons of Guided Media

1000GHz/km

HighlightHighHighFO

HighheavyMediumHighCoax

lowmediumlowLowTP

safetyweightratecostitemsmedia

Overview 39

(review)

Unguided Transmission Media

~ transmission and reception are achieved by antenna forradiation and pickup EM (ElectroMagnetic) energy into/from medium with no physical connection (wireless)

- Radio Frequency (RF) :

* freq. < 2 MHz : via ground wave propagation

- follow creature of the earth; pass through obstacle/building

* 2 ~ 30 MHz : via sky wave propagation

- bounce back by ionosphere layer; may absorbed by rain

* freq. > 30 MHz: Line-Of-Sight (LOS) propagation (straight)- Blocked by obstacles and diverges in space (multipath

fading : signals arrived via different paths and cancels/destroys to one another)

Overview 40

Telecommunication Spectrum – by FCCTelecommunication Spectrum – by FCC(review)

3 3

VF ~ voice Freq., E - Extremely; V – Very; U – Ultra; S - Super

|Ultravioletlight

Overview 41

(brief)

Two types of wireless transmission

- Infrared (IR) : 3 1011 ~ 2 1014 Hz

~ wireless communication w/o antenna (portable)

~ limited to small area (single room)

1. Omni-directional Electromagnetic (EM) waves

- Broadcast radio : 30 MHz ~ 1 GHz

2. Directional EM waves

- Point-to-Point Satellite Channel :Varieties: 4/6 , 12/14 , and 19/29 GHz (downlink/uplink frequency)

- Satellite Microwave : 2 GHz ~ 40 GHz, Optimal: 1~10GHz

- Limited broadcast (spot beam)

- Laser beam : straight line and may be blockedOverview 42

(review)

Effects of Signal Propagation

• Propagation in free space always like light (straight line)

• Receiving power proportional to 1/d² power law

(d = distance between sender and receiver)

• Receiving power additionally influenced by

– fading (frequency dependent)

– Shadowing (or even worse, blocking)

– reflection at large obstacles

– scattering at small obstacles

– diffraction at edges

shadowing reflection scattering diffraction

Overview 43

(review)

Multipath propagation

• Signal can take many different paths between sender and

receiver due to reflection, scattering, and diffraction

(spreading effect)

signal at sendersignal at receiver

~ dispersion effect in optic fiber

Overview 44

Network ComponentsNetwork ComponentsSooooo…

• Networks are COMPLEX

• Consists of MANY pieces . . .

- devices (computers/hosts)

- nodes (switches/routers/computers)

- links (various media: wired or wireless)

- Lots of (layered) Protocols

- Various of Applications

- Miscellaneous hardwares and softwares

• Two key elements:- Network topology- Protocols and Network architecture

Overview 45

• Protocols ~ a set of (standard) rules that specifies

- Format of messages

- Meaning of messages

- Rules of exchange

- Procedures for handling problems

~ Designed in Layers (layered communications)

- separation of networking functions to simplify

network design (reducing complexity and more …)

• Layers + Protocols form a Protocol stack/suite

(several software modules)

~ called Network Architecture

• Protocols ~ a set of (standard) rules that specifies

- Format of messages

- Meaning of messages

- Rules of exchange

- Procedures for handling problems

~ Designed in LayersLayers (layered communications)(layered communications)

-- separation of networking functions to simplify

network design (reducing complexity and more …)

• Layers + Protocols form a Protocol stack/suite

(several software modules)

~ called Network Architecture

裏

Network ArchitectureOverview 46

•• In LayeredIn Layered communicationscommunications

- an entityentity of a particular layerlayer can only communicate with :

(1) adjacent layer entities via serviceservice interfacesinterfaces

(service viewpoint) or Service Access Point, SAPSAP)

?

??

(for your information)

- above ~ to provide services- below ~ to ask for (receive) services

(2) peer layer entity via peer protocolsprotocols

~ to logically transfer messages for a session to be built-up

* ServiceService interface ~ define the physical data flow between layers* Peer protocolprotocol ~ define the logical data exchange and

peer-to-peer logicallogical communications

(Q: How to approach the goal ?)

Overview 47

Layer and Peer Protocol InteractionLayer and Peer Protocol Interaction

To sum up, for each layer : to above--service providerto below--service userin between--service interface

• Service Protocol; (can be) totally separated

• Service object descriptions w/o specifying “how to do it?”• Protocol rules for (monitoring) entities’ communication• Entity uses protocols (which can be changed) to define its

services (which is unchanged, i.e., invisible to users).

N layer entityN layer entity

Layer N+1protocol

Layer N-1 protocol

Layer N/N-1interface

Layer N+1/Ninterface

Layer N protocol

Peer-to-peer

N+1 layer entity N+1 layer entity

N-1 layer entity N-1 layer entity

Overview 48

OSI Reference ModelOSI Reference Model

• Proposed by ISO for OSI (OpenSystem Interconnection)

• Started in 1977; completed in 1983 “ISO standard 7498”

• A reference model for computercommunication architecture andprotocol development

• Layered model just provides aframework, but not defines or constrains an implementation

• Developed per-layer protocol/

standard, but not very successful.

OSI 7OSI 7--layer modellayer model

Reg

ardi

ngto

dat

atr

ansp

ort

Reg

ardi

ngto

app

licat

ions

Overview 49

Why a layered Network Model ? (advantages ?)Why a layered Network Model ? (advantages ?)

• Layers: each layer implements a service . . .- via its own internal-layer actions- relying on services provided by layer below

• Reducing complexity~ divide interrelated aspects of networking

• Standardizing interfaces (physical)~ define interfaces for PnP compatibility and multivendor integration

• Facilitating modular engineering~ specialize development/implementation efforts on modular functions

• Accelerating technique evolution~ prevent change dependency, so each layer can evolve quickly

• Simplifying teaching and learning~ divide internetworking into discrete and easily learned subsets

Overview 50

OSI 7-layer : A Top-Down ViewOSI 7-layer : A Top-Down View

• Application layer (Layer 7)

~ Provides network access to application programs and users

~ Issues:

- everything is application specific

~ Example: Telnet (Remote login), File Transfer Protocol (FTP)

Electronic mail service, X-terminal (terminal emulation)

• Presentation layer (Layer 6)

~ Responsible for the format/transformation of data to be

exchanged between applications

~ Issues: - Syntax (character code) & semantics conversion

- Data compression(encoding)/decompression

- Cryptography (Encryption & Decryption)

~ Example: ASN.1, OSI presentation protocol

Overview 51

• Session layer (Layer 5)

~ Supports the dialog between cooperating application programs

~ Issues: - Session/dialog establishment/maintenance/termination

- Synchronization of dialog

- Recovery (from error) or backup via checkpoints

~ Example: ISO session protocol, RPC (Remote Procedure Call)

(The lower four layers provide reliable data exchange and quality of service.)

• Transport layer (Layer 4)

~ Controls the delivery of messages/data between the end stations

(at a pre-negotiated service quality) (e.g., reliable ?)

~ Issues: - Connection establishment/management/termination

- Error control and/or flow/congestion control(if required)

~ Example: TCP, UDP, SPX (Netware’s Sequenced Packet eXchange)Overview 52

• Network layer (Layer 3)

~ transfer of data between end systems across a communication

network

~ Issues: - Addressing (locating a host in the network)- Routing (data packet forwarding) & Congestion control

~ Example: IP (Internet Protocol), IPX, CCITT X.25 (network layer)

• Data Link layer (Layer 2)

~ Provides reliable transfer of block information (the frame) over a link

(between two physically connected end system on a link basis)

~ Issues: - Synchronization (framing)- Error control*- Flow control

~ Example: ISO HDLC (High Level Data Control), IEEE 802.2 LLC

CCITT LAPD (Link Access Procedure-D channel), X-modem

(InterPacket eXchange Protocol)

Overview 53

Remark:

- Layer 4 and above (referred to “higher layer”) are End-to-End

protocols (executed only on host computer)

- Not all 7 layers are needed

- Many layered protocol architectures do not define the session

or the presentation layer. ( Example )

- Define sublayers if necessary (later on)

• Physical layer (Layer 1)

~ Concerned with (only) transmission of bits over a communicationchannel (transmission media)

~ Issues: - Conversion of bits into electrical or optical signal- Encoding & Decoding- Scrambling & Descrambling

~ Example: CCITT X.21, RS-232(unbalanced), RS-449 (balanced)

Overview 54

MODEM Example

Overview 55

FTP Operation - Combining higher layers

Host A (FTP client) Host B (FTP server)

Internetwork

Control connection (at initial)

Data connection (by request)

AP L.C.

PL L.C.

SL L.C.

Overview 56

SummarySummary -- OSI LayersOSI Layers

- Physical ~ transmission of bits over communicationchannel (transmission media)

- Data link ~ Provides reliable transfer of block information(the frame) over a link

- Network ~ packet forwarding (addressing + routing)

- Transport ~ Controls the way of data delivery betweenstations/nodes

- Session ~ dialog between cooperating application programs(login and password)

- Presentation ~ data representation of information and compatibility

- Application ~ individual application program for users

Overview 57

OSI model in Point-to-Point Communication

• How are data transmitted under the OSI model ?

PDU

Encapsulation Decapsulation

100110101101010201101000010 . . .

Physical (transmission media)(via channel or network)

Data

Message

Information

bits

Frame

Packet

Segment

Signal

Overview 58

Protocol Layering Networked Communication

Transport

Presentation

Session

Data Link

Physical

Network

Application

Transport

Presentation

Session

Data Link

Physical

Network

Application

Station/Host A Station/Host B

IS or Node

network

IS (Intermediate System) :L7 Gateway*L3 RouterL2 Switch/BridgeL1 Hub/Repeater

Data Link

Physical

Network

Data Link

Physical

Network

Data Link

Physical

Network

Data Link

Physical

Network(protocol stack inOne computer)

IS - so called Intermediate Message Processor,IMP (refer to ISO Network Hierarchy)

L3L2L1

datadata datadata

datadata

Overview 59

Internet Protocol StackInternet Protocol Stack

• Application: supporting networkapplications– FTP, SMTP, HTTP, SMTP, POP3

• Transport: host-host data transfer– TCP, UDP

• Network: routing of datagrams fromsource to destination– IP,ICMP, IGMP, RIP,OSPF, BGP4

• Link: data transfer between neighboringnetwork elements– PPP/SLIP, Ethernet, Token-Ring

• Physical: bits “on the wire” - transmission

application

transport

network

link

physical

Network Access

Overview 60

Layering: logical communication

Ex: transport layer• take data from appl.

• add addressing, reliability check info to form “datagram”

• send datagram to peer

• wait for peer to Ackreceipt

applicationtransportnetwork

linkphysical

transport

applicationtransportnetwork

linkphysical

transport

applicationtransportnetwork

linkphysical application

transportnetwork

linkphysical

networklink

physical

data

data

Logical comm.

data

ack

Overview 61

Layering: physical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

dataHost A

Host B

Overview 62

Protocol layering and data• Each layer takes data from upper (lower)

– Adds (take off) header information to create new data unit– Does what the action(s) indicated by the header– passes new data unit to layer below (above)

Higher-layer see nothing pealed off; Lower-layer cannot see misunderstood

applicationtransportnetwork

linkphysical

source

applicationtransportnetwork

linkphysical

destinationMMMM

Ht

HtHnHtHnHl

MMMM

Ht

HtHnHtHnHl

messagesegmentdatagramframe

Encapsulation Decapsulation

network(s)

Overview 63

Protocol Data Unit (PDU) in TCP/IP Architecture

TCP header IP header

DLL Frame

InternetProtocolStack

DLL header

Host A

NIC

Meaningful to appropriate peerprotocol software module Overview 64

PDU Decomposition in TCP/IP Scenario

Windows> telnet 140.124.70.26 (showing the first packet transmitted by the src PC)

Protocol #: Network--Transport layer

Source’s MAC addressDest.’s MAC address

Protocol type: DLC--Network layer

Overview 65

(PDU cont’d)

Src port # (randomly generated by the src PC)Dest port # (an well-known for well-known application)

Port #: Transport--Application layer

(More on Layer communication)Overview 66

Layering: internetworking communication(summary)

(Layer 3 device)(Layer 2 device)

hostIS (Intermediate Systems) :

L7 Gateway*L3 RouterL2 Switch/BridgeL1 Hub/Repeater

Anything below 2 or above 3 ?

• Hosts, routers, switches, and bridges; each contains a different set of layers, reflecting their differences in functionality.

Overview 67

IEEE 802 ProjectIEEE 802 Project

• IEEE 802.1 High Level Interface

• IEEE 802.2 LLC (Logical Link Control) Working Group

• IEEE 802.3 CSMA/CD (Carrier Sense Multiple Access with

Collision Detection)**

• IEEE 802.4 Token-Bus WG

• IEEE 802.5 Token-Ring WG

• IEEE 802.6 DQDB (Distributed Queue Dual Bus) [MANWG]

• IEEE 802.7 Broadband Technical Advisory Group

• IEEE 802.8 Fiber Optic Technical Advisory Group

• IEEE 802.9 Integrated Voice and Data LAN Working Group

• IEEE 802.10 LAN Security Working Group

• IEEE 802.11 Wireless LAN (WLAN)**

• IEEE 802.12 Demand-Priority (100VG-AnyLAN)

Ethernet

ARCnet

IBM token-ring

LM

SG

Overview 68

More on IEEE 802.xMore on IEEE 802.x• IEEE 802.14

– Cable-TV based broadband communication network• IEEE 802.15

– Wireless personal area network (WPAN) **• IEEE 802.16

– Broadband wireless access (BBWA) **• IEEE 802.17

– Resilient Packet Ring Working Group• IEEE 802.18

– Radio Regulatory TAG• IEEE 802.19

– Coexistence Technical Advisory Group (coexistence with existing standards and other standards)

• IEEE 802.20– Wide area broadband wireless access (WBWA)

(Most of them are in hibernation.)

Overview 69

Issues of DLC in DLLIssues of DLC in DLL

• Physical layer

~ concerns sending signalssignals over a transmission (physical) link

• Data link layer

~ a logic added above physical interface~ concerns sending datadata over a communication link

• With a Data Link Control protocol, the transmission media between systems is referred to as a data link.

• Major issues

- Framing (Frame synchronization) - Flow control- Error detection and error control - Addressing- Exchange of data, control Link and management

Sublayer concept

Overview 70

Medium Access ControlMedium Access Control

• Why separate DLL to sublayers - LLC and MAC ?

- many DLL w/o access mechanism to a sharedshared--accessaccess medium

- under the same LLC, several MAC options may be provided

• MAC sublayer appends control information at the front and back

of LLC PDU, forming a MAC frame

• Multiple Access

- a set of rules to control the access to a sharedcommunication medium(called channel)

- conflicting access to the channel may be happened- mostly for broadcasting channels- Ex: shared-media LANs (such as Ethernet-Bus, wireless)

Overview 71

OSI’s DLL vs IEEE 802.2 (LLC and MAC)OSI’s DLL vs IEEE 802.2 (LLC and MAC)

• LLC (Logical Link Control (LLC) ) sublayer- refers upward to higher-layer software functions (using IEEE 802.2)

- provides for environments that need connectionless and connection-oriented

• MAC (Media Access Control (MAC) ) sublayer

- refers downward to lower-layer hardware functions (using IEEE 802.3x )

- provides access to the LAN medium in an orderly manner.- several MAC options may be provided for the same LLC

Medium Access Control (MAC)

DLLsublayers

Logical link Logical link ControlControl (LLC)(LLC)Data

LinkLayer

Splitting

Especially in LAN environments

Overview 72

Calls for Addressing ( )Calls for AddressingCalls for Addressing (( ))

• Mechanisms needed to distinguish among . . .

- multiple networks on the Internet (internetworking)

- multiple computers on a network

- multiple applications (software) on a computer

- multiple copies of specific single application ona computer

(entity, )

. . .

End-point (in TCP/IP-based Internet)

Overview 73

Data Link Layer’s Address

• Data-link layer address

- uniquely identifies each physical network connection of a device

- also referred to as physical or hardware address

- usually exist within a flat address space

Data Link Layer’s Address

pre-established and typically fixed relationship to a specific device

MAC/NIC address in a LAN Overview 74

Physical/MAC Address – the NIC’s ID

DFE 540TX

RJ-45 Jack NIC ~ Network Interface Card ( )ID ~ identifier ( )

Overview 75

Check with your MAC Address via “ winipcfg ”

Manufacturer’s ID NIC’s ID/Serial number

242 's

IEEE’s EIU-48 rule

* Alternate: “ipconfig -all”, “netstat –r” command under MS NT/2000/XP Overview 76

Connection-Oriented and Connectionless ServicesConnection-Oriented and Connectionless Services

• Connection-Oriented (CO) service- Sending and receiving station establish a real/virtual connection

before data is transmitted

- All frames/packets are guaranteed to arrive and are to arrive in order

- Ex: VCPS(at NL), TCP(at TL), FTP(at APL), ATM(at DLL)

• Connectionless (CL) service- Sending station sends a sequence of independent frames/packets to

the receiving station with no dedicated/fixed path- Intermediate nodes are forwarding packets with their best-effort- Receiving of frame/Packet can be acknowledged (with retransmission)

or no acknowledged (with no retransmission) ACK by the receiver- Ex: DGPS(at NL), UDP(at TL), SNMP(at APL), IP (at NL)

(between end-systems)