Post on 26-Dec-2015
CS671 Advanced Computer Networking
Chen QianFall 2014
IntroductionCQ (2014)
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What you can learn
Basic knowledge of conventional Internet Protocols layers
Introduction of current hot topics in networking Wireless and mobile networks Data center networking Software defined networking Future Internet
Research skills in system and network area Presentation skills
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Wireless networks
IntroductionC. Q. (8/13)
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Cloud Computing
IntroductionC. Q. (8/13)
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Data centers
IntroductionC. Q. (8/13)
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Data centers
IntroductionC. Q. (8/13)
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Data center networks
IntroductionC. Q. (8/13)
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Future Internet
Content-based network? (YouTube, Netflix, etc.)
Most devices are mobile? (smartphones, laptops, touch pads, etc.)
IntroductionC. Q. (8/13)
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Lecture 1: Introduction
1.1 What is the Internet?1.2 Network edge
end systems, access networks, links
1.3 Network corepacket switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers
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What’s the Internet: “nuts and bolts” view
millions of connected computing devices: hosts = end systems running network apps: Web
browser, YouTube, Skype, etc.
router
PC
server
wirelesslaptop
cellular handheld
wiredlinks
access points
communication links fiber, copper, radio, satellite transmission rate = bandwidth
routers: forward packets (chunks of data)
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What’s the Internet: “nuts and bolts” view Internet: “network of
networks” loosely hierarchical public Internet versus
private intranet
protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, DNS,
Ethernet
Home network
Institutional network
Mobile network
Global ISP
Regional ISP
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What’s the Internet: a service view
communication services provided to apps: reliable data delivery
from source to destination
• File transfer, email, E-bank.
“best effort” (unreliable) data delivery
• Multimedia (cell phone, video streaming, VoIP)
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What’s a protocol?human protocols: “Homework
assignment” Turn in
“I have a question” Explain
… specific msgs sent… specific actions
taken when msgs received, or other events
network protocols: machines rather than
humans all communication
activity in Internet governed by protocols
protocols define format, order of msgs sent and
received among network entities, and actions taken on msg transmission, receipt
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What’s a protocol?a human protocol and a computer network protocol:
Hi
Hi
Got thetime?
2:00
TCP connection request
TCP connectionresponseGet http://www.cs.uky.edu/~qian
<file>time
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Chapter 1: roadmap
1.1 What is the Internet?1.2 Network edge
end systems, access networks, links
1.3 Network corepacket switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers
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A closer look at network structure:
network edge: applications and hosts
access networks, physical media: wired, wireless communication links
network core: interconnected
routers network of networks
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The network edge: end systems (hosts):
run application programs e.g. Web, email at “edge of network”
client/server
peer-peer
client/server model client host requests, receives
service from always-on server e.g. Web browser/server;
email client/server peer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype, BitTorrent
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Access networks and physical media
Q: How to connect end systems to edge router?
residential access nets institutional access
networks (school, company)
mobile access networks
Keep in mind: bandwidth (bits per
second) of access network?
shared or dedicated?
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100 Mbps
100 Mbps
100 Mbps1 Gbps
server
Ethernetswitch
Institutionalrouter
To Institution’sISP
Ethernet Internet access
Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into
Ethernet switch
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Wireless access networks
shared wireless access network connects end system to router via base station aka “access
point”
wireless LANs: 802.11b/g (WiFi): 11 or 54
Mbps
wider-area wireless access provided by telco operators ~1 Mbps over cellular system
(3G) WiMAX promises 10’s Mbps
over wide area
basestation
mobilehosts
router
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Home networks
Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point
wirelessaccess point
wirelesslaptops
router/firewall
cablemodem
to/fromcable
headend
Ethernet
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Chapter 1: roadmap
1.1 What is the Internet?1.2 Network edge
end systems, access networks, links
1.3 Network core packet switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers
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The Network Core
mesh of interconnected routers
the fundamental question: how is data transferred through net? circuit switching:
dedicated circuit per call: telephone net
packet-switching: data sent thru net in discrete “chunks”
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Packet Switching
Sequence of A & B packets does not have fixed pattern bandwidth shared on demand queueing delay, packet loss
A
B
C100 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
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store-and-forward
store and forward: entire packet must arrive at router before it can be transmitted on next link
A file/message larger than maximum packet size is transmitted as multiple packets
R R RL
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Network Core: Packet Switching
each end-end data stream divided into packets
packets of different users share network resources
each packet uses full link bandwidth
resources used as needed
resource contention: aggregate resource
demand can exceed amount available
congestion: packets queue, wait for link use
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Packet Switching versus Message Switching
Smaller end-to-end delay from pipelining Less data loss from transmission errors
Advantages of packet switching
More header bits Additional work to do segmentation
and reassembly
Disadvantages of packet switching
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Packet switching versus circuit switching
1 Mb/s link each user:
100 kb/s when “active”
active 10% of time (a “bursty” user)
circuit-switching: 10 users
packet switching: with 35 users,
probability > 10 active at same time is less than .0004
Packet switching allows more users to use network!
N users
1 Mbps link
Q: how did we get value 0.0004?
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Packet switching versus circuit switching
great for bursty data resource sharing simpler, no call setup
excessive congestion: packet delay and loss protocols needed for reliable data transfer,
congestion control Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps
solution may impact network neutrality
Is packet switching a “slam dunk winner?”
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Internet structure: network of networks
roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,
Cable and Wireless), national/international coverage treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
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Tier-1 ISP: e.g., Sprint
…
to/from customers
peering
to/from backbone
….
………
POP: point-of-presence
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Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider
Tier-2 ISPs also peer privately with each other.
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Internet structure: network of networks
“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet
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Internet structure: network of networks
a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
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Chapter 1: roadmap
1.1 What is the Internet?1.2 Network edge
end systems, access networks, links
1.3 Network corepacket switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers
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How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link
capacity packets queue, wait for turn
A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
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Four sources of packet delay
1. nodal processing: check bit errors determine output link
A
B
propagation
transmission
nodalprocessing queueing
2. queueing time waiting at output
link for transmission depends on congestion
level of router
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Delay in packet-switched networks3. Transmission delay: R=link bandwidth
(bps) L=packet length (bits) time to send bits into
link = L/R
4. Propagation delay: d = length of physical
link s = propagation speed in
medium (~2x108 m/sec) propagation delay = d/s
A
B
propagation
transmission
nodalprocessing queueing
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End-to-End Delay Nodal delay (from when last bit of packet arrives at this
node to when last bit arrives at next node)
dnodal = dproc + dqueue + dtrans + dprop
End-to-end delay over N identical nodes/links from client c to server s (from when last bit of packet leaves client to when last bit arrives at server)
dc-s = dprop + Ndnodal
Round trip time (RTT)RTT = dc-s + ds-c + tserver
where tserver is server processing time
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Implications of end-to-end delay Relative importance of bandwidth and “distance”
for a small message (e.g. 1 byte), distance(1 ms vs. 100 ms propagation time) is moreimportant than bandwidth (1 Mbps vs. 100 Mbps)
for a large message (e.g., 25 Mbyte),bandwidth is more important than distance
Delay x Bandwidth productExample:
for 100 ms end to end delay and 45 Mbps bandwidth,there can be up to 560 Kbyte of data in flight
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Throughput
throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time
server, withfile of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec pipe that can carry
fluid at rate
Rs bits/sec
pipe that can carryfluid at rate
Rc bits/sec
server sends bits
(fluid) into pipe
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Throughput (more)
Rs < Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
Rs > Rc What is average end-end throughput?
Rs bits/sec Rc bits/sec
link on end-end path that constrains end-end throughput
bottleneck link
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Throughput: Internet scenario
10 connections (fairly) share backbone bottleneck link R
bits/sec
Rs
Rs
Rs
Rc
Rc
Rc
R
per-connection end-end throughput: min(Rc,Rs,R/10)
in practice: Rc or Rs is often bottleneck
Or the server is the bottleneck
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Chapter 1: roadmap
1.1 What is the Internet?1.2 Network edge
end systems, access networks, links
1.3 Network corepacket switching, network structure
1.4 Delay, loss and throughput in packet-switched networks
1.5 Protocol layers
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Protocol “Layers”Networks are
complex! many “pieces”:
hosts routers links of various
media applications protocols hardware,
software
Question: Is there any hope of organizing structure of
network?
Or at least our discussion of networks?
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Layered architecture Use abstraction to hide
complexity Each layer
• provides a service via its own internal actions as well as relying on service provided by layer below
• is a network of processes Can have alternative
abstractions at each layer (resulting in protocol graph rather than protocol stack)
Application programs
Process-to-process channels
Host-to-host connectivity
Hardware
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Each protocol
involves two or more peers two interfaces defined
• service interface: operations a local user can perform on a protocol entity and get results
• peer-peer interface: form and meaning of messages exchanged by protocol entities (also called peers) to provide protocol service
term “protocol” generally used to refer to peer-peer spec
High-level entity
High-level entity
Protocol entity
Protocol entity
Serviceinterface
Peer-to-peer
interface
Host 1 Host 2
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Internet protocol stack application: supporting network
applications FTP, SMTP, HTTP
transport: process-process data transfer TCP, UDP
network: routing of datagrams from source to destination IP, routing protocols
link: data transfer between neighboring network elements PPP, Ethernet
physical: bits “on the wire”
application
transport
network
link
physical
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ISO/OSI reference model presentation: allow applications
to interpret meaning of data, e.g., encryption, compression, machine-specific conventions
session: synchronization, checkpointing, recovery of data exchange
Internet stack “missing” these layers! these services, if needed, must
be implemented in application
application
presentation
session
transport
network
link
physical
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Logical communication between peers
E.g.: transport accept data from
application add addressing,
reliability check info to form a message
send message to peer via a delivery service
wait for peer’s reply (ack)
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
transport
transport
ack
data
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Physical path of dataEach layer takes data (service data unit) from above adds header to create its own protocol data unit passes protocol data unit to layer below
network
link
physical
network
link
physical
application
transport
network
link
physical
source
host
destination
host
message
segment
datagram
frame
M
MH 4
MH 4H 3
MH 4H 3H 2 T2
bits
application
transport
network
link
physical
router routerprotocol data units
...
More terminology: A switch is a relay with two layers (physical and link). A repeater is a relay with only the physical layer.
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Introduction: SummaryCovered a “ton” of material! Internet components: hosts, links, routers,
Internet what’s a protocol? network edge, core, access network
packet-switching versus circuit-switching
Internet structure: ISPs performance: loss, delay, throughput layering
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End of Lecture01