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Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

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Page 1: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Data NetworksSecond Edition

Dimitri Bertsekas / Robert Gallager

Page 2: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Chapter 1

Introduction and Layered Network Architecture

Page 3: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Section 1.1

Historical Overview

Page 4: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.1 Historical Overview

Page 5: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Historical Overview(60’s)

Page 6: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Historical Overview(70’s)

Page 7: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Historical Overview(70’s) Inside subnet, nodes &

communication links. IMP(Interface message processors) :

to route message through subnets. – called also switches.

wide area network local area network

Page 8: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Historical Overview(80’s)

Page 9: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Historical Overview(80’s) 1980‘s, more and more networks

connected via gateways and bridges

Each subnet has its own conventions and control algorithms (protocols) for handling data – gateways and bridges must deal with this inhomogeneity.

Page 10: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Historical Overview In the future, data network, voice

networks, cable networks will be integrated more. ISDN(integrated services digital

network) Broadband ISDN : greater data rates.

Page 11: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Section 1.2

Messages and Switching

Page 12: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.2.1 Messages and Packets

message: Airline reservation system : data,

flight no# … Email : document File system : file Image transmission system : image …

Page 13: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.2.1 Messages and Packets

A message is usually a string of binary symbols, 0 or 1 (bit).

Sender → message → recipient

compression Compression can reduce expected

length of representation.

Page 14: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Messages and Packets Control overhead : ensure reliable

communication route control congestion, etc.

Usually broken into shorter bit strings(packets)※ transmit long messages is harmful ,

(e.g. delay, buffer management, congestion control)

Page 15: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.2.2 Sessions In larger transaction : a message

sequence is called a session. Requires many messages over a

considerable time period. Setup procedure(similar to setting up a

call) A connection

In other networks, no such setup is required. Each message is treated independently → connectionless

Page 16: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Sessions Messages within a session are

triggered by events. Message initiation times are arbitrary,

unpredictable. Model messages / packets arrival for

a given session as a random process. Poisson process On/Off flow model Application are rapidly changing →

model complex

Page 17: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Sessions Detailed characteristics for

applications.1. Message arrival rate and variability

of arrivals.2. Session holding time.3. Expected message length and

length distribution.4. Allowable delay : 10ms ~ 1ms

Page 18: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Sessions

5. Reliability : error-free 、 occasional loss.

6. Message and packet orderinge.g. file transfer : message arrival rate :

10w delay requirement

: relaxed reliability : high

Page 19: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.2.3 Circuit Switching and Store-and-Forward Switching Circuit switching

Inefficient utilization When a session s is initialed,

allocated a given transmission rate rs

(bits per second) A path is created from transmitting

site through the subnet to destination site.

Page 20: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit switching Each communication link on this path

allocates a portion of rs of its total transmission capacity.(done by TDM or FDM multiplexing)

Note : sum of rates for all sessions cannot exceed total capacity of links, otherwise, new session is rejected.

Guaranteed transmission rate rs similar to telephone network.

But, in a data network, required transmission rates are different and vary over a wide range

Page 21: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit Switching Why inefficient?

:message arrival rate :expected interarrival rate b/w

messages for a given session :expected tx time of a message :expected length of messages

1

1

xL

Page 22: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit Switching So

Note

srLx /

busyisStotimeoffractiontox /1

timeidlex ,1

Page 23: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit Switching Fig.1.5

Page 24: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit Switching

delay allowable

meet enough to large bemust

nUtilizatio

) 1 (i.e.1 If

delayn Propagatiotx time

Tdelay expected allowable If

.e. r i

x λ

/λTλT

λTxλ

P: ,: xT ; Px

s

Page 25: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit Switching Session for which are

referred to “bursty” sessions For interactive terminal sessions,

Link costs become less important wasted capacity of circuit switching:less important

1T

%1:nutilizatio,01.0 T

Page 26: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Circuit Switching and Store-and-Forward

Switching Store-and-forward Switching

Without making reservation/allocation Using full transmission rate of the link

on packet/message basis Advantage

Fully utilized , whenever has traffic to send

Disadvantage Queuing delay,hard to control,overloaded

nodes => need to be slowed down

Page 27: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Store-and-Forward Switching

Message Switching Store-and-forwarding,messages basis

Packet Switching Store-and-forwarding,packets basis

Page 28: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Store-and-Forward Switching

Virtual Circuit routing Store-and-forwarding,but a particular

path is set up when a session initiated using a fixed path

Capacity is allocated on a demand basis

Dynamic routing Store-and-forwarding,packets find its

own path according to current information available at nodes visited

Page 29: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Section 1.3

Layering

Page 30: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Laying Hierarchical modularity

Page 31: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Laying(Fig 1.7)

Page 32: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Laying OSI(Open System Interconnection)

model by ISO(International Standards Organization)

Page 33: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Laying(Fig 1.8)

Page 34: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.1 Physical Layer Provide a virtual link for transmitting

a sequence of bits between any pair of nodes

Map incoming bits from the next higher layer into signals for the channel At Rx end,map signals back to bits

Modem(digital data Modulator and demodulator) : broadly referred here

Page 35: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Physical Layer compare

Synchronous bit pipe 1bit per t second

Intermittent synchronous bit pipe DLC module supplies bits at a synchronous rate

when has data Asynchronous characters

Map into fixed-length bit strings and transmitted asynchronously as they are generated

Page 36: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Physical Layer Interface between DLC

Module on one end might be temporarily inoperable

Some initialization is required For synchronous operation , must

provide timing

Page 37: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Physical Layer RS-232-C & physical layer of X.21

DCE:Data Communication Equipment DTE: Data Terminal Equipment

DTE sends a signal to DCE “request-to-send”.DCE replies with “clear-to-send”

The interchange is a very simple example of a protocol or distributed algorithm

Page 38: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.2 Data Link Control (DLC) Layer

To convert unreliable bit pipe at layer 1 into higher-layer

Sending packets asynchronously but error-free Variable delay b/w packet into DLC exit from

the other end Need to correct errors

Overhead control bits Header trailer

Page 39: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Data Link Control (DLC) Layer

Some request retransmissions when error occur

For some LAN,multi-access may take place.

The signal received is a function of the signals from a multiplicity of transmitting nodes

Page 40: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

MAC(Medium Access Control) Sublayer

Considered as lower sublayer of layer 2

Allocate multi-access channel , so that each node can successfully transmit its frame without interference from other nodes

Page 41: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

MAC(Fig 1.10)

Page 42: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.3 Network Layer Implementing routing and flow

control for its network Use packet header along with

stored information to accomplish these functions

Transport layer also provides additional information as a set of parameters in accordance with interface protocol

Page 43: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer(Fig 1.11)

Page 44: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer Along with transmit packets from lower

layer and new packets from higher layer,the network layer generates its own control packets

For virtual circuit routing Select a route when VC being

generated(distributed way or by source node)

Ensure each packet of the session follows the assigned route(by placing enough information in the header)

Page 45: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer For datagram network,each packet

is routed individually Service offered

Using VC Packet in order,connection - oriented

Using datagram Packets out of order,connectionless

service

Page 46: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer Flow control

Avoid sending data too fast Congestion control

Avoid congestion within subnet Solution

Good route Good buffer management Control flow of packet into network s.t.

congestion control

Page 47: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer Connection – oriented service

Possible to negotiate => guarantee service at setup

Connectionless service No opportunity for negotiate

Page 48: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer High link capacities in the future will make

it possible to operate network economically with low utilization and make flow control unnecessary

Unfortunately,as link capacity increase,access rate into networks also increase e.g. malfunctioning user could dump enough

data into network quickly to cause congestion => still need some regulatry rule

Page 49: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer Routing & flow control

Primarily for WAN For LAN , routing is not a major

problem,congestion is possible Could be dealt with in MAC sublayer Major functions of network layer are

accomplished in MAC sublayer. Thus,connectionless service is common

here.

Page 50: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Network Layer Note

Network layer delivering every packet may be reliable or might be unreliable.

The higher layer might have to recover errors

Page 51: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Internet Sublayer To connect different subnetworks together

Solution: create a new sublayer:internet sublayer top part of network layer

A gateway connecting two subnets will interface

Internet modules also : routing & flow control

Note Bridges interface at DLC layer.For LAN , routing

& flow control are done in MAC.

Page 52: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.4 Transport layer Break messages into packets , and

reassembles packets Might multiplex several low-rate

sessions all from same source and going to same destination

Might split one high-rate session into multiple sessions(flow control)

If network layer is unreliable,achieve reliable end-to-end connection

End-to-end flow control

Page 53: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.5 Session layer Provide transport layer with

information needed to establish the session

Achieve load sharing b/w many processors

Access rights in setting up sessions Who pay for the service Handle interaction b/w 2 end points

Page 54: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.6 Presentation layer Data encryption Data compression Code conversion

Page 55: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

1.3.7 Application layer Consideration variation in service

offered by various layers Sometimes , not conform to OSI

model e.g.ATM ( Asynchronous Transfer

Mode ) , broadband ISDN

Page 56: Data Networks Second Edition Dimitri Bertsekas / Robert Gallager

Section 1.4

A Simple Distributed Algorithm problem