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1: Introduction 1

Computer Networks

6th

Semester 2008 -

Section CS & IT

10:20am 12:50am Tuesday &11:10am

12:50am Thursday

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1: Introduction 2

Computer Networks

Instructor: Vihang Garg

([email protected]) Required Text: Computer Networks by

Andrew S. Tanenbaum(0-13-066102-3)

Reference Texts Computer Networking - ATop-Down Approach Featuring the Internet,

3rd

edition, Kurose-Ross (ISBN: 0-321-22735-2)

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1: Introduction 3

Course Objectives

Pass the UPTU exam

Learn computer networks with emphasis on thepractical applications that most of you see and use

every day. Nota study of the OSI model, or older technologies

and protocols.

Nota certification course for Network Specialists. Nota study of network hardware or data

communications equipment

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1: Introduction 4

Course Administration & Policies Grading Policy

Quizzes (6) Major Exams/Tests (2) Programs/Projects (2) Final presentation

Low Attendance will be strictly dealt with

General Rule:General Rule: If not immediately after class thenIm not in!

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1: Introduction 5

Whats this all about??

What really happenswhen I?

How does my email getfrom point a to point b?

What do all thesenetwork buzzwordsmean to me?

Why does my browserrespond slowly at times?

How does an IP addressactually find a web site?

applicationtransportnetworkdata linkphysical

applicationtransport

networkdata linkphysical

request

reply

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1: Introduction 6

Learning Approach: Traditional

Introduction and Networking Overview (Ch. 1) Overview of network components and the Internet

Medium Access Sublayer Between data link and physical layers

The Network Layer & Routing How your data finds its way

The Transport Layer Why your data gets there

The Application Layer

How you get work done in the network

Application

Presentation

Session

Transport

Network

Data Link

Physical

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1: Introduction 7

Chapter 1 Introduction tocomputernetworks

An overview of computer networking

which introduces many key concepts andterminology. Sets the stage for futuretopics.

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1: Introduction 8

RoadMap

Computer Networks Introduction

uses

classification

Switching Circuit switched

Packet Switched

Delay Analysis

Protocol and Layers

Services and Interface

OSI Model

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1: Introduction 9

Chapter 1: Introduction

What is a Computer Network?

What is the difference between ComputerNetwork and Distributed Network?

Collection of interconnected

but independent computers

A computer network in which

independent computers are

transparent to the user

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1: Introduction 10

Uses of Computer Networks

Business Applications

Home ApplicationsMobile Users

Social Issues

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1: Introduction 11


Business Applications

request

reply

Resource sharing

High reliability

File sharing

Performance

Scalability

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1: Introduction 12


Home ApplicationsAccess to remote information

Person to person communication

Interactive entertainment

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1: Introduction 13

Classification of Network

Computer Networks

Transmission technology

Broadcast network

E.g., Airport annoucement

Point to Point networkE.g., Telephonic conversation

Scale

Local AreaNetwork

MAN

WAN

Wireless

Internet

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1: Introduction 14

Classification of Network

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1: Introduction 15

Local Area Network

Local Area Network

10m to 1000m

10 to 100 mbps (BUS)

4 to 16 mbps (Ring)

Low delay and few errors

Channel allocation issue

Centralized/decentralized

(a) Bus (b) Ring

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1: Introduction 16

Metropolitan Area Network

A metropolitan area network based on cable TV.

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1: Introduction 17

Metropolitan Area Network

A metropolitan area network based on Dual Bus.

Direction of flow on bus A

Direction of flow on bus B

1 2 3

10km (802.6)

DQDB (Distributed Queue Dual Bus) 802.6

No switching, bus head initiates activity

E.g., cable television,

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1: Introduction 18

Wide Area Network

100km to 1000km Hosts and communication subnet

Packet and data switching

Topology of subnet is symmetric

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1: Introduction 19

Wide Area Network

Relation between hosts on LANs and the subnet.

a.) Star b.) Ring c.) Tree d.) Complete e.) IntersectingRings f.) Irregular

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1: Introduction 20

Wireless Network

Relation between hosts on LANs and the subnet.

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1: Introduction 21

Wireless Network

(a) Individual mobile computers (b) A flying LAN

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1: Introduction 22

Wireless Network

(a) Bluetooth configuration (b) Wireless LAN

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1: Introduction 23

Internetworks/Internet millions of connected

computing devices: hosts,end-systems PCs workstations, servers PDAs, phones, toasters

running network apps

communication links fiber, copper, radio,

satellite transmission rate =

bandwidth

routers/switches:forward packets (chunks

of data) betweennetworks

local ISP

company

network

regional ISP

router workstation

server

mobile

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1: Introduction 24

Cool

Internet Appliances

Pepper Pad

Game Console

IP picture frame

Web-enabled toaster+weather forecaster

Cisco Wireless IPPhone 7920

PalmOne TreoSmartPhone

Sony Mylo

Personal Communicator

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1: Introduction 25

Internetworks/Internet

protocolscontrol sending,receiving of msgs

e.g., TCP, IP, HTTP, FTP, PPP Internet:network of

networks

loosely hierarchical public Internet versus

private intranet

Internet standards RFC: Request for comments

IETF: Internet EngineeringTask Force

local ISP

company

network

regional ISP

router workstation

server

mobile
http://www.rfc-editor.org/rfcsearch.htmlhttp://www.rfc-editor.org/rfcsearch.html

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1: Introduction 26

RoadMap


uses

classification

Switching Circuit switched

Packet Switched

Delay Analysis

Protocol and Layers Services and Interface

OSI Model

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1: Introduction 27

Switching

Switching Methods

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

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1: Introduction 28

Circuit Switching

End to end resources

reservedfor call dedicated resources: no

sharing

dedicated circuit-like(guaranteed) performance

call setup required

First Automatic circuit switching was developed byan undertaker Almon B Strowger.

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1: Introduction 29

Circuit Switching

(a)

Circuit switching.

(b) Packet switching.

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1: Introduction 30

Circuit Switching

network resources(e.g., bandwidth)

divided into pieces pieces allocated to calls resource piece idleif

not used by owning call(no sharing) dividing link bandwidth

into pieces frequency division

(FDM) time division (TDM)

TDM:

frequency

time

frequency

time

FDM:

1234

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1: Introduction 31

Circuit Switching TDM Example

T1 Circuit 1.536 Mbps bandwidth,

24 time slots 500msec setup time

Yields:

1.536Mbps/24 =64Kbps per slot or circuit

How long to send: 80KByte file?

1MByte file?

(80 * 103

* 8) / (64 * 10

3

) = 640/64 = 10 (+ 0.5 sec = 10.5 sec)(1 * 106

* 8

) / (64 * 103 ) = 8000/64 = 125 (+ 0.5 sec = 125.5 sec)

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1: Introduction 33

Packet Switching

Packet-switching versus circuit switching

A

B

C10 MbpsEthernet

1.536 Mbps

45 Mbps

D E

statistical multiplexing

queue

of packets

waiting for output

link

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1: Introduction 34

Packet-switching: store-and-forward

Takes L/R seconds totransmit (push out)packet of L bits onto

link or R bps Entire packet must

arrive at router before

it can be transmittedon next link: store andforward

delaytrans = 3L/R

Example: L = 7.5 Mbits

R = 1.5 Mbps

delay (transmission) =15 sec

message switching

vs.

packet switching

R R R

L

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1: Introduction 35

Packet Switching: Message Segmenting

Now break up the message

into 5000 packets

Each packet 1,500 bits

1 msec to transmit eachpacket on one link

pipelining:each linkworks in parallel

Delaytrans reduced from15 sec to 5.002 sec

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1: Introduction 36

Packet switching versus circuit switching

1 Mbps link

each user: generates traffic at

100Kbps when active

is active 10% of time

Capacity:

circuit-switching: 10 users

packet switching: with 35 users,

probability > 10 activeless than .0004

Packet switching allows more users to use (i.e. share) thenetwork!

N users

1 Mbps link

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1: Introduction 37

Packet switching versus circuit switching

Great for bursty data

resource sharing

no call setup

Excessive congestion (load): 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

and real-time applications

Is packet switching a slam dunk winner?

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1: Introduction 38

Packet-switched networks:

routing/forwarding Goal:move packets through routers from the source

(router) to the destination (router)

well study several path selection algorithms datagram network:

destination addressdetermines next hop

routes may change during session analogy: driving, asking directions

virtual circuit network:

each packet carries tag (virtual circuit ID), tagdetermines next hop

fixed path determined at call setup time, remains fixedthru call

routers/switches maintain per-call state

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1: Introduction 39

Message Switching

(a) Circuit switching (b) Message switching (c) Packet

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1: Introduction 40

Packet Switching

A comparison of circuit switched and packet-switchednetworks.

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1: Introduction 41

Implementation of Connection-Oriented

ServiceRouting within a virtual-circuit subnet.

f l d

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1: Introduction 42

Comparison of Virtual-Circuit and

Datagram Subnets

5-4

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1: Introduction 43

RoadMap


uses

classification

Switching Circuit switched Packet Switched

Delay Analysis


OSI Model

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1: Introduction 44

Delay Analysispackets experience delay

on end-to-end path

four sources of delayat each hop

nodal processing delay: check bit errors determine output link

queuing delay: time waiting at output

link for transmission

depends on congestionlevel of router

A

B

propagation

transmission

nodal

processing queuing

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1: Introduction 45

Delay in packet-switched networks

Transmission delay:

R=link bandwidth (bps)

L=packet length (bits) time to send bits into

link = L/R

Propagation delay:

d = length of physical link

s = propagation speed inmedium (~2x108 m/sec)

propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queuing

Note: s and R are verydifferent quantities!

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1: Introduction 46

Four sources of packet delay

A

B

propagation

transmission

nodalprocessing queuing

Packet-to-packet variance??

Nodal processing (dproc)?

Transmission (dtrans)?

Propagation (dprop)?

Queuing (dqueue)?

C l

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1: Introduction 47

Caravan analogy

Cars propagate at100 km/hr

Toll booth takes 12 sec toservice a car (data rate =5 cars per minute)

car~bit; caravan ~ packet Q: How long until caravan

is lined up before 2nd tollbooth?

Time to push entirecaravan through toll

booth onto highway = 10cars/(5 cars per minute)= 2 minutes

Time for last car to

propagate from 1st to2nd toll both:100km/(100km/hr)= 1 hr

A: 62 minutes

toll

booth

toll

booth

ten-carcaravan

100 km 100 km

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1: Introduction 48

Nodal delay

dproc = processing delay typically a few microsecs or less

dqueue = queuing delay depends on congestion

dtrans = transmission delay

= L/R, significant for low-speed links dprop = propagation delay

a few microsecs to hundreds of msecs

proptransqueueprocnodal ddddd +++=

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1: Introduction 49

Queuing delay (revisited)

R=link bandwidth (bps)

L=packet length (bits) a=average packet

arrival rate

traffic intensity = La/R

La/R ~ 0: average queuing delay small

La/R -> 1: delays become large

La/R > 1: more work arriving than can be

serviced, average delay infinite!

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1: Introduction 50

Packet loss

queue (aka: buffer) preceding link in router

has finite capacitywhen packet arrives at a full queue, packet

is dropped (aka: lost)

lost packet may be retransmitted byprevious node, by source end system, ornot retransmitted at all

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1: Introduction 51

RoadMap


uses

classification


Delay Analysis


OSI Model

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1: Introduction 52

Whats a protocol?

human protocols: What time is it?

I have a question Introducing people

to each other

specific messagessent

specific actions taken

when messagesreceived, or otherevents

network protocols: machines rather than

humans all communicationactivity in the Internetis governed by

protocols

protocols defineformat,order of

messages sent and receivedamong network entities, and

actions taken on message

transmission and/or receipt

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1: Introduction 53

Whats a protocol?

a human protocol: a computer network protocol:

Q: Other human protocols?

Hi

Hi

Got thetime?

2:00Get http://www.awl.com/kurose-ross

TCP connectionreq

TCP connectionresponse

time

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1: Introduction 54

Protocol Layers

Networks are complex!

many pieces:

hostsrouters

links of various

mediaapplications

protocols

hardware,software

Question:Is there any hope of

organizing

the

structure of network?

Or at least our discussionof networks?

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1: Introduction 55

Organization of air travel

a series of steps

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

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1: Introduction 57

Layered air travel: servicesservicesview

Counter-to-counter delivery of person+bags

baggage-claim-to-baggage-claim delivery

people transfer: loading gate to arrival gate

runway-to-runway delivery of plane

airplane routing from source to destination

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1: Introduction 58

Distributed

implementation of layer functionality

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Depar

tingair

port

arriv

ingairp

ort

intermediate air traffic sites

airplane routing airplane routing

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1: Introduction 59

Protocol Hierarchies

Set of layers and protocol is called a Network Architecture

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1: Introduction 60

Layering: physical communication

applicationtransportnetwork

linkphysical

application

transportnetwork

linkphysical

application

transportnetwork

linkphysical

application

transportnetwork

linkphysical

networklink

physical

data

data

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1: Introduction 61

S

ending

node

R

eceivin

gnode

Protocol layering and data

Physical transmission

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1: Introduction 62

Design Issues for the Layers

Addressing Identify one process in one machine

Data Transfer Rules Simplex /duplex

No of logical channels

Error Control Ordering and data loss

Flow Control Preserving order of packets

Slow receiver for fast transmitter

Multiplexing

Routing

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1: Introduction 63

RoadMap


uses classification


Delay Analysis


OSI Model

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1: Introduction 66

Service Primitives (2)

Packets sent in a simple client-server interaction

on a connection-oriented network.

Services to Protocols

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1: Introduction 67

Services to Protocols

Relationship

The relationship between a service and a protocol.

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1: Introduction 68

RoadMap


uses classification


Delay Analysis


OSI Model

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1: Introduction 69

How are layers selected in OSI

Layer should represent a level of abstraction

Perform a well defined function Function of each layer should define international

standards

Layer boundaries should minimize information flow

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1: Introduction 70

OSI

End to

End

l k

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1: Introduction 71

OSI protocol stack

application: supporting network applications ftp, smtp, http

Presentation: Standard encoding for data Session: Allows Users on different

machines to establish session transport: host-host data transfer

tcp, udp

network: routing of datagrams from sourceto destination ip, routing protocols

Data link: data transfer betweenneighboring network elements Simplex stop and wait,sliding window

physical: bits on the wire

application

transport

network

link

physical

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P l i D il

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1: Introduction 73

Protocols in Detail

network: routing of datagrams from source todestination

Static tables wired into the network/dynamic tables,which are modified during data transfer Handles traffic information for accounts Handles problems with hetrogeneous networks

Data link: data transfer between neighboringnetwork elements Breaks into frames

Decides frame boundaries Receives acknowledgement for frames Retransmission of frames Flow control and error handling Pigybacking incase of two way channel Channel access protocol by medium access sublayer

R f M d l (2)

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1: Introduction 74

Reference Models (2)

The TCP/IP reference model.

R dM

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1: Introduction 75

RoadMap

ISDN

BackBone ARPANET

NSFNET

TIER-1 backbone Physical Media

ISDN(Integrated services

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1: Introduction 76

ISDN(Integrated services

digital network)Transfer voice and other data

N-ISDN 64kbpsDigital bite pipe for data transfer

Support multiple independent channel by

time division multiplexing

NT1ISDN

Exchange

T U

ISDN

Telephone

ISDN

Terminal

ISDN C t

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1: Introduction 77

ISDN Cont

B-ISDN 155 Mbps (ATM over packetswitching)

ATM (Asynchronous Transfer Mode

Connected using a CAT 5 cable

R dM

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1: Introduction 78

RoadMap

ISDN

BackBone ARPANET

NSFNET


Th ARPANET

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1: Introduction 79

The ARPANET

(a) Structure of the telephone system. (b) Barans proposed distributed switching

system.

Th ARPANET (2)

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1: Introduction 80

The ARPANET (2)

The original ARPANET design.

IMP(Interface message processor)DARPA(Defense Advance Research Project Agency)

Th ARPANET (3)

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1: Introduction 81

The ARPANET (3)

Growth of the ARPANET (a) December 1969. (b)July 1970.

(c) March 1971. (d) April 1972. (e) September1972.

NSFNET

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1: Introduction 82

NSFNET

The NSFNET backbone in 1988.

CSNET was formed with one computer and dial up to ARPANET

Six computers formed the backbone(San Diego,Princeton,Ithaca)

First TCP/IP WAN

20 regional networks connected to the backbone formed NSFNET

I t t t t t k f t k

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1: Introduction 83

Internet structure: network of networks

roughly hierarchical

at center: tier-1 ISPs (e.g., Sprint, AT&T, MCI,

Level3, Qwest, Cable & Wireless), national/international coverage

treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1providersinterconnect(peer)privately

NAP

Tier-1 providers

also interconnectat public networkaccess points(NAPs/MAEs)

Ti 1 ISP: S i t

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1: Introduction 84

Tier-1 ISP: e.g., SprintSprint US backbone network

Ti 1 ISP: MCI

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1: Introduction 85

Tier-1 ISP: e.g., MCI

MCI U.S. backbone network

Tier 1 ISP: e MCI

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1: Introduction 86

Tier-1 ISP: e.g., MCI

MCI US-Intercontinental backbone network

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1: Introduction 88


Tier-3 ISPs and local ISPs last hop (access) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

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 arecustomersofhigher tierISPs

connectingthem to restof Internet

Real Internet delays and routes

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1: Introduction 89

Real

Internet delays and routes

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms

7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *

19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

traceroute:

gaia.cs.umass.edu

to www.eurecom.fr

Three delay measurements fromgaia.cs.umass.edu

to cs-gw.cs.umass.edu

* means no response (probe lost, router not replying)

trans-oceaniclink

RoadMap

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1: Introduction 90

RoadMap

ISDN

BackBone ARPANET

NSFNET


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Twisted Pair (U hi ld d t i t d P i )

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1: Introduction 92

Twisted Pair (Unshielded twisted Pair)

(a) Category 3 UTP.(b) Category 5 UTP.

Twisting is for less electrical interference

CAT 5 has more twists and is Teflon coated to reduce crosstalk

Coaxial Cable

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1: Introduction 93

Coaxial Cable

A coaxial cable.

50 Ohms and 75 Ohms

It can span longer distances than twisted pair

Fiber Optics

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1: Introduction 94

Fiber Optics

glass fiber carrying light

pulseshigh-speed operation:

100Mbps Ethernet

high-speed point-to-pointtransmission (e.g., 50,000 Gbps)

low error rate

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Fiber Cables

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1: Introduction 96

Fiber Cables

(a) Side view of a single fiber.(b) End view of a sheath with threefibers.

Fiber Cables (2)

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1: Introduction 97

Fiber Cables (2)

A comparison of semiconductor diodes andLEDs

as light sources.

Fiber Optic Networks

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1: Introduction 98

Fiber Optic Networks

A fiber optic ring with active repeaters.

Wireless Transmission

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1: Introduction 99

Wireless Transmission

The Electromagnetic Spectrum

Radio Transmission

Microwave Transmission

Infrared and Millimeter Waves Lightwave Transmission


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1: Introduction 100


The electromagnetic spectrum and its usesfor communication.

Radio Transmission

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1: Introduction 101

Radio Transmission

(a)

In the VLF, LF, and MF bands, radio waves follow

the curvature of the earth.

(b) In the HF band, they bounce off the ionosphere.

Politics of the Electromagnetic

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1: Introduction 102

SpectrumThe ISM bands in the United States.

Lightwave Transmission

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1: Introduction 103

Lightwave

Transmission

Convection currents can interfere with lasercommunication systems.

A bidirectional system with two lasers is pictured here.

Communication Satellites

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1: Introduction 104


Geostationary Satellites

Medium-Earth Orbit Satellites

Low-Earth Orbit Satellites

Satellites versus Fiber


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1: Introduction 105


Communication satellites and some of theirproperties, including altitude above the earth,

round-trip delay time and number of satellitesneeded for global coverage.

Communication Satellites (2)

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1: Introduction 106


The principal satellite bands.


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1: Introduction 107


VSATs using a hub.

Low-Earth Orbit Satellites

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1: Introduction 108

Iridium

(a)

The Iridium satellites from six necklaces around the

earth.(b) 1628 moving cells cover the earth.

(a) (b)

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1: Introduction 1

Medium Access Sublayer

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The Channel Allocation Problem

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1: Introduction 3

The Channel Allocation Problem

Static Channel Allocation in LANs andMANs

Dynamic Channel Allocation in LANs andMANs

Static Channel Allocation

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1: Introduction 4

Static Channel Allocation

FDM

TDMT-Mean Time Delay

1/

bits/frame (based on probability density)

C-capacity in bps

-

Arrival rate in frames/sec

Tfdm-Mean Time Delay for FDM channel

T = 1/ C- Tfdm

= 1*N/ C-

Dynamic Channel Allocation in LANs andMANs

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1: Introduction 5

MANs

Station Model. N independent stations.

Single Channel Assumption.

Collision Assumption.

(a) Continuous Time.(b) Slotted Time.

(a) Carrier Sense.(b) No Carrier Sense.

Multiple Access Protocols

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1: Introduction 6

Multiple Access Protocols

ALOHA Carrier Sense Multiple Access Protocols Collision-Free Protocols Limited-Contention Protocols Wavelength Division Multiple AccessProtocols Wireless LAN Protocols

Pure ALOHA

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1: Introduction 7

Pure ALOHA

In pure ALOHA, frames are transmitted atcompletely arbitrary times.

Pure ALOHA (2)

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1: Introduction 8

ur LOH ( )

Vulnerable period for the shaded frame.

Pure ALOHA (3)

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1: Introduction 9

L ( )

Throughput versus offered traffic forALOHA systems.

Error Detection and Correction

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1: Introduction 10

Error-Correcting Codes

Error-Detecting Codes

Hamming Code

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1: Introduction 11

g

Hamming code is a linear error-correcting

Hamming codes can detect and correctsingle-bit errors

Hamming Distance is the minimum number

of bit any codeword may differ.To detect an (d) bit errors we need (d+1)

bits.

To correct (d) bit errors we need (2d+1)bits

Hamming Code

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1: Introduction 12

g

Hamming Code

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1: Introduction 13

g

Hamming Code for Bursty Data

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1: Introduction 14

g y

Use of a Hamming code to correct bursterrors.

Polynomial Code (CRC)

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1: Introduction 15

y ( )

Cyclic redundancy code (CRC)Sender and receiver agree upon a

generator G(x) of r bits G(x) must have starting and ending 1s Data frame must be longer than G(x)

Append r bit 0s to polynomial x^r M(x) -r- is the number of bits in G(x) 1.

Divide x^r M(x) by G(x) using modulo 2Substract the remainder from x^r M(x)

using modulo 2

Error-Detecting Codes

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1: Introduction 16

g

Calculation of the polynomial code checksum.

Elementary Data Link Protocols

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1: Introduction 17

y


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1: Introduction 18

y

Network Layer packet is wrapped with aheader and is called frame

Layers are independent


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1: Introduction 19

y

An Unrestricted Simplex Protocol

A Simplex Stop-and-Wait Protocol

A Simplex Protocol for a Noisy

Channel

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ProtocolDefinitions

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1: Introduction 21

Definitions (ctd.)

Some definitions

needed in theprotocols to follow.

These are located in

the file protocol.h.

Unrestricted Simplex Protocol

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1: Introduction 22

p

Assumptions Both transmitter and receiver are always ready

Infinite buffer capacity

No data is lost or frames are damaged

No sequence number or acknowledgementrequired

Data flow is unidirectional

Also called Utopia

Unrestricted

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1: Introduction 23

SimplexProtocol

Simplex Stop-and-Wait Protocol

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1: Introduction 24

Assumtions Buffer size is not infinite

Sender may flood the receiver

Data flow is unidirectional

Simplex

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1: Introduction 25

Stop-and- WaitProtocol

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A Simplex Protocol for a NoisyChannel

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1: Introduction 27

Channel

A positiveacknowledgement

with retransmission

protocol.

Continued

A Simplex Protocol for a Noisy Channel(ctd.)

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1: Introduction 28

(ctd.)

A positive acknowledgement with retransmission protocol.

Sliding Window Protocols

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1: Introduction 29

Data transfer is bi-directional

Piggybacking may be used to increaseperformance

Separate number system at sender to

number packetsSeparate number system at receiver to

acknowledge packet

Sliding Window Protocols

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1: Introduction 30

A One-Bit Sliding WindowProtocol

A Protocol Using Go Back N A Protocol Using SelectiveRepeat

Sliding Window Protocols (2)

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1: Introduction 31

A sliding window of size 1, with a 3-bit sequence number.

(a) Initially.(b)

After the first frame has been sent.

(c)

After the first frame has been received.

(d) After the first acknowledgement has been received.

A One-Bit Sliding Window

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1: Introduction 32

Protocol

Continued

A One-Bit Sliding Window Protocol(ctd.)

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1: Introduction 33

(ctd.)

A Protocol Using Go Back N

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1: Introduction 34

Pipelining and error recovery. Effect on an error when

(a)

Receivers window size is 1.

(b) Receivers window size is large.

IEEE Standards

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1: Introduction 35

Collectively called as IEEE 802. The standard differ at physical and MAC layer

Compatible at the data link layer.

1.

CSMA/CD (802.3)

2.

Token Bus (802.4)

3.

Token ring. (802.5)

CSMA/CD (802.3)

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1: Introduction 36

Ethernet Cabling

Manchester Encoding

The Ethernet MAC Sublayer Protocol

The Binary Exponential Backoff Algorithm

Ethernet PerformanceSwitched Ethernet

Ethernet Cabling

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1: Introduction 37

The most common kinds of Ethernet cabling.

Ethernet Cabling (2)

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1: Introduction 38

Three kinds of Ethernet cabling.

(a)

10Base5, (b)

10Base2, (c)

10Base-T.


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1: Introduction 39

Cable topologies. (a) Linear, (b) Spine, (c)Tree, (d) Segmented.


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1: Introduction 40

(a) Binary encoding, (b) Manchester encoding,(c) Differential Manchester encoding.

Ethernet MAC Sublayer Protocol

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1: Introduction 41

Protocol

Frame formats. (b) IEEE 802.3.

Ethernet MAC Sublayer Protocol (2)

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1: Introduction 42

Protocol ( )

Collision detection can take as long as 2 .

Binary Back Off Algorithm

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1: Introduction 43

((2^i)-1) is the time slots a station waitsbefore resending.

i is the number of collisions

After 10 collisions the interval is 1023

slotsAfter 16 slots the controller reports

failure to the higher layers.

Ethernet Performance

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1: Introduction 44

Efficiency of Ethernet at 10 Mbps with 512- bit slot times.

Switched Ethernet

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1: Introduction 45

A simple example of switched Ethernet.

Token Bus (802.4)

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1: Introduction 46

Logical Token Ring is formed

N stations and each takes T sec, max wait NT sec

02.4 allows addition/deletion in the ring

Token Bus (802.4)

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1: Introduction 47

802.4 frame format

Destenationaddress

Sourceaddress

Data Checksum

Preamble

Start Delimiter

Frame Control End Delimiter

Token Bus (802.4)

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1: Introduction 48

Four priorities 0,2,4 and 6 with 6 is highest

Four separate queues for each priority

Each frame can transmit 5 times than 802.3

Token Bus (802.4)

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1: Introduction 49

Control framesClaim Token Claim token during ring

initializationSolicit_Successor1 Allows station to enter the ring

Solicit_Successor1 Allows station to enter the ringWho_follows Recover from lost token

Resolve_Contention Used when multiple station wants

to sendToken Pass the token

Set_Successor Allow station to leave the ring

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The Network Layer

Chapter 5

Roadmap

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Network Layer design issues

Routing Algorithms Congestion Control

Internetworking

TCP and IP packets

Network Layer Design Isues

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Store-and-Forward Packet Switching

Services Provided to the Transport Layer Implementation of Connectionless Service

Implementation of Connection-Oriented Service

Comparison of Virtual-Circuit and Datagram Subnets

Store-and-Forward Packet Switching

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The environment of the network layer protocols.

fig 5-1

Services Provided to the Transport

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Layera) Independent of the subnet

b) Transport Layer should be shielded from the number, type andtopology of the subnet.

c) Network address to transport layer is independent of the numbering

plan (even across LANs and WANs)

Implementation of Connectionless Service

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Routing within a diagram subnet.

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Comparison of Virtual-Circuit andDatagram Subnets

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5-4

Roadmap

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Internetworking

TCP and IP packets

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Routing Algorithms

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A Routing Algorithm is the part of the network layer responsible

for deciding which output line an incoming packet should be

transmitted.

Nonadaptive routing: does not consider measurements and

estimates of current traffic and topology. (also called static routing)

Adaptive routing: changes routing decisions to reflect changes in

topology.

The Optimality Principle

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If a router J is on the optimal path from router I to K then the optimalpath from J to K is also along the same route.

Shortest Path Routing (static)

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The first 5 steps used in computing the shortest path from A to D.

The arrows indicate the working node.

Shortest Path Routing

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Dijkstra's algorithm to compute the shortest path through a graph.

5-8 top

Shortest Path Routing

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Dijkstra's algorithm to compute the shortest path through a graph.

5-8

bottom

Flooding

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a) A static routing algorithm

b) Incoming packet is sent to all outgoing lines except the one it came

c) Sequence number and hop counter control floodingd) Selective flooding is when routers send packets that are in correct

direction

distance-vector routing

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a) used in packet-switched networks for computer communications

b) It uses the Bellman-Ford algorithm to calculate paths.

Details are given in the word document

Distance Vector Routing (2)

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The count-to-infinity problem.

Good news travels fast and bed news travels slow

Link State Routing

E h t t d th f ll i

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Each router must do the following:

1. Discover its neighbors, learn their network address.

2. Measure the delay or cost to each of its neighbors.3. Construct a packet telling all it has just learned.

4. Send this packet to all other routers.

5. Compute the shortest path to every other router.

Examples are OSPF and IS-IS (Intermediate System-Intermediate System)

Learning about the Neighbors

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(a) Nine routers and a LAN. (b) A graph model of(a).

Measuring Line Cost

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A subnet in which the East and West parts are connected by two lines.

Building Link State Packets

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(a) A subnet. (b) The link state packets for this subnet.

Hierarchical Routing

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Hierarchical routing.

Broadcast Routing

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Reverse path forwarding. (a) A subnet. (b) a Sink tree. (c) The

tree built by reverse path forwarding.

Multicast Routing

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(a) A network. (b) A spanning tree for the leftmost router.

(c) A multicast tree for group 1. (d) A multicast tree for group 2.

Routing for Mobile Hosts

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A WAN to which LANs, MANs, and wireless cells are attached.

Routing for Mobile Hosts (2)

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Packet routing for mobile users.

(b) Examples of the finger tables.

Roadmap

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Internetworking

TCP and IP packets

Congestion Control Algorithms

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General Principles of Congestion Control

Congestion Prevention Policies

Congestion Control in Virtual-Circuit Subnets

Congestion Control in Datagram Subnets

Load Shedding

Jitter Control

Congestion

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When too much traffic is offered, congestion sets in and

performance degrades sharply.

General Principles of Congestion Control

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1. Monitor the system .

detect when and where congestion occurs.2. Pass information to where action can be taken.

3. Adjust system operation to correct the problem.

Congestion Prevention Policies

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Policies that affect congestion.

5-26

Congestion Control in Virtual-Circuit

Subnets

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(a) A congested subnet. (b) A redrawn subnet, eliminates

congestion and a virtual circuit from A to B.

Hop-by-Hop

Choke Packets

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Choke Packets

(a) A choke packet that affects

only the source.

(b) A choke packet that affects

each hop it passes through.

Jitter Control

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(a) High jitter. (b) Low jitter.

Quality of Service

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Requirements

Techniques for Achieving Good Quality of Service

Integrated Services

Differentiated Services

Label Switching and MPLS

Requirements

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How stringent the quality-of-service requirements are.

5-30

Buffering

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Smoothing the output stream by buffering packets.

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The Leaky

Bucket

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Bucket

Algorithm(a) Input to a leaky bucket.

(b) Output from a leakybucket. Output from a token

bucket with capacities of(c)

250 KB, (d) 500 KB, (e)750 KB, (f) Output from a

500KB token bucket feeding

a 10-MB/sec leaky bucket.

The Token Bucket Algorithm

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(a) Before. (b) After.

5-34

Admission Control

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An example of flow specification.

5-34

Packet Scheduling

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(a) A router with five packets queued for line O.

(b) Finishing times for the five packets.

RSVP-The ReSerVation Protocol

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(a) A network, (b) The multicast spanning tree for host 1.

(c) The multicast spanning tree for host 2.

RSVP-The ReSerVation Protocol (2)

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(a) Host 3 requests a channel to host 1. (b) Host 3 then requests a

second channel, to host 2. (c) Host 5 requests a channel to host 1.

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Assured Forwarding

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A possible implementation of the data flow for assured forwarding.

Label Switching and MPLS

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Transmitting a TCP segment using IP, MPLS, and PPP.

Internetworking

How Networks Differ

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How Networks Differ

How Networks Can Be Connected

Concatenated Virtual Circuits

Connectionless Internetworking

Tunneling Internetwork Routing

Fragmentation

Connecting Networks

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A collection of interconnected networks.

How Networks Differ

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Some of the many ways networks can differ.

5-43

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Concatenated Virtual Circuits

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Internetworking using concatenated virtual circuits.

Connectionless Internetworking

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A connectionless internet.

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Tunneling (2)

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Tunneling a car from France to England.

Internetwork Routing

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(a) An internetwork. (b) A graph of the internetwork.

Fragmentation

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(a) Transparent fragmentation. (b) Nontransparent fragmentation.

Fragmentation (2)

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Fragmentation when the elementary data size is 1 byte.

(a) Original packet, containing 10 data bytes.

(b) Fragments after passing through a network with maximumpacket size of 8 payload bytes plus header.

(c) Fragments after passing through a size 5 gateway.

The Network Layer in the Internet

The IP Protocol

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The IP Protocol

IP Addresses

Internet Control Protocols

OSPF The Interior Gateway Routing Protocol

BGP The Exterior Gateway Routing Protocol

Internet Multicasting

Mobile IP

IPv6

Design Principles for Internet

1. Make sure it works.

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2. Keep it simple.

3. Make clear choices.4. Exploit modularity.

5. Expect heterogeneity.

6. Avoid static options and parameters.

7. Look for a good design; it need not be perfect.

8. Be strict when sending and tolerant when receiving.

9. Think about scalability.

10. Consider performance and cost.

Collection of Subnetworks

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The Internet is an interconnected collection of many networks.

The IP Protocol

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The IPv4 (Internet Protocol) header.

The IP Protocol (2)

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Some of the IP options.

5-54

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IP Addresses (2)

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Special IP addresses.

Subnets

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A campus network consisting of LANs for various departments.

Subnets (2)

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A class B network subnetted into 64 subnets.

CDR Classless InterDomain Routing

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A set of IP address assignments.

5-59

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Internet Control Message Protocol

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The principal ICMP message types.

5-61

ARP The Address Resolution Protocol

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Three interconnected /24 networks: two Ethernets and an FDDI ring.

Dynamic Host Configuration Protocol

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Operation of DHCP.

OSPF The Interior Gateway Routing

Protocol

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(a) An autonomous system. (b) A graph representation of (a).

OSPF (2)

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The relation between ASes, backbones, and areas in OSPF.

OSPF (3)

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The five types of OSPF messeges.

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BGP The Exterior Gateway RoutingProtocol

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(a) A set of BGP routers. (b) Information sent to F.

The Main IPv6 Header

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The IPv6 fixed header (required).

Extension Headers

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IPv6 extension headers.

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Extension Headers (2)

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The hop-by-hop extension header for large datagrams (jumbograms).

Extension Headers (3)

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cn chaptr 1,2,3

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