Brooks/Cole, 2003Chapter 6ComputerNetworksBrooks/Cole, 2003Understand the rationale for the existence of networks.Understand the rationale for the existence of networks.Distinguish between the three types of networks: LANs Distinguish between the three types of networks: LANs !ANs and "ANs.!ANs and "ANs.After reading this chapter, the reader should After reading this chapter, the reader should be able to:be able to:OOBJECT!E"BJECT!E"List different connecting de#ices and the $%& layers in List different connecting de#ices and the $%& layers in which each de#ice operates.which each de#ice operates.Understand client'ser#er (odels.Understand client'ser#er (odels. Understand the $%& (odel and )C*+&*.Understand the $%& (odel and )C*+&*.Brooks/Cole, 2003NETWORKS, NETWORKS, LARGE AND SMALLLARGE AND SMALL6.16.1Brooks/Cole, 2003A A computer networkcomputer network is a combination is a combination of systems connected through of systems connected through transmission media.transmission media.Local area network (Local area network (LANLAN))Metropolitan (Metropolitan () area network ) area network ((MANMAN))Wide area network (Wide area network (WANWAN))Brooks/Cole, 2003A A modelmodel is the specification set by a is the specification set by a standards organization as a standards organization as a guideline guideline for designing networks.for designing networks.A A protocolprotocol is a set of is a set of rulesrules that that controls the interaction of different controls the interaction of different deices in a network or an deices in a network or an internetwork.internetwork.Brooks/Cole, 2003OSI MODELOSI MODEL6.26.2Brooks/Cole, 2003The Open Systems The Open Systems Interconnection (OSI) modelInterconnection (OSI) modelis a theoretical model that is a theoretical model that shows how any two diferent shows how any two diferent systems can systems can communicatecommunicate with each other.with each other.Note:Note:Brooks/Cole, 2003Figure 6-1The OSI modelFigure 6-2Flow of data in the OSI modelHeaderHeaderHeaderTrailerBrooks/Cole, 2003!hysical layer!hysical layer"ata#link layer"ata#link layerNetwork layerNetwork layer$ransport layer$ransport layer%ession layer%ession layer!resentation layer!resentation layerApplication layerApplication layerBrooks/Cole, 2003$he physical layer is responsible for $he physical layer is responsible for transmitting a transmitting a bit streambit stream oer a oer a physical medium.physical medium.&t encodes and decodes bits into &t encodes and decodes bits into groups of bitsgroups of bits..&t then transforms a stream of bits into &t then transforms a stream of bits into a a signalsignal..Brooks/Cole, 2003$he data#link layer organizes bits into $he data#link layer organizes bits into logical unitslogical units called called framesframes..$he data#link layer is responsible only $he data#link layer is responsible only for for node#to#node delierynode#to#node deliery of the frame.of the frame.$he data#link layer is often $he data#link layer is often responsible for responsible for error handling error handling between two ad'acent stationsbetween two ad'acent stations..Brooks/Cole, 2003$he network layer is responsible for $he network layer is responsible for deliery of adeliery of a packetpacket between the between the original source and final destination.original source and final destination.(sing (sing logical addresses (&! addresses)logical addresses (&! addresses) instead of physical addresses.instead of physical addresses.)*ample of &! address)*ample of &! address+,-.+.../0.+.+ (, 1ytes)+,-.+.../0.+.+ (, 1ytes)Brooks/Cole, 2003$he transport layer is responsible for $he transport layer is responsible for source#to#destination deliery of the source#to#destination deliery of the entire entire messagemessage..$he transport layer is responsible for $he transport layer is responsible for breaking the breaking the entire messageentire message into into seeral seeral packetspackets and deliery them to the network and deliery them to the network layer.layer.$he transport layer is responsible for $he transport layer is responsible for ensuring that the whole message is ensuring that the whole message is transmitted.transmitted.&f packets arrie &f packets arrie out of orderout of order2 they must be 2 they must be reorganized.reorganized.Brooks/Cole, 2003$he session layer is designed to control the $he session layer is designed to control the dialogdialog between users.between users.$he $he synchronization (synchronization () points) points diides a long message into smaller ones diides a long message into smaller ones and ensure that each section is receied and ensure that each section is receied and acknowledged by the receier.and acknowledged by the receier.Most network implementationsMost network implementations todaytoday do do notnot use a separate session layer2 their sericesuse a separate session layer2 their sericesare usually included in theare usually included in the applicationapplication layer.layer.Brooks/Cole, 2003$he presentation layer is concerned with the $he presentation layer is concerned with the synta* and semantics of the synta* and semantics of the information information e*changede*changed between two systems.between two systems.&t deals with the fact that different systems &t deals with the fact that different systems use use different coding methodsdifferent coding methods..3ompress ( 3ompress ( ) and decompress ( ) and decompress ( ) data ) data)ncrypt ( )ncrypt ( ) and decrypt ( ) and decrypt ( ) data ) dataMost implementations doMost implementations do notnot use a use a presentation layer presentation layer today2today2 their sericesare their sericesare usually included in other layer.usually included in other layer.Brooks/Cole, 2003$he application layer enables the$he application layer enables the useruser to access the network.to access the network.&t defines &t defines common applicationscommon applications that that can be implemented to make the 'ob can be implemented to make the 'ob of the user of the user simplersimpler..Will be discussed later4Will be discussed later4Brooks/Cole, 2003CATEGORIES CATEGORIES OFOFNETWORKSNETWORKS6.36.3Brooks/Cole, 2003Figure 6-3Categories of networksBrooks/Cole, 2003Figure 6-4L!sBrooks/Cole, 2003Bus topologyBus topologyWhen a station sends a frame to another When a station sends a frame to another computer,computer, all all computer receiver the frame computer receiver the frame and check its destination address.and check its destination address.Star topologyStar topologyHub (all, like a bus) v.s. sitch (one)Hub (all, like a bus) v.s. sitch (one)!ing topology!ing topologyWhen a computer needs to send a frame to When a computer needs to send a frame to another computer, it sends it to its another computer, it sends it to its neighborneighbor..Brooks/Cole, 2003Figure 6-"#!Figure 6-6$!Brooks/Cole, 2003W"# is the connection of individual W"# is the connection of individual computers or $"#s over a computers or $"#s over a large arealarge area.." person using a telephone line to " person using a telephone line to connect to an %S& is using a W"#.connect to an %S& is using a W"#.%S&' internet service provider%S&' internet service providerBrooks/Cole, 2003CONNECTINGCONNECTINGDEVICESDEVICES6.46.4Brooks/Cole, 2003Figure 6-%Conne&ting de'i&esBrooks/Cole, 2003Figure 6-()e*eater" repeater is an electronic device and operate " repeater is an electronic device and operate only in the only in the physical layerphysical layer of the of the (S% (S% model.model." repeater can " repeater can regenerateregenerate the signal and the signal and sendsend it to the rest of the netork.it to the rest of the netork.Brooks/Cole, 2003Repeaters operate at the frst Repeaters operate at the frst layer(physical layer) of thelayer(physical layer) of theOSI model.OSI model.Note:Note:Brooks/Cole, 2003Figure 6-+,ridgeBrooks/Cole, 2003%n bus topology, a bridge is a traffic %n bus topology, a bridge is a traffic controller.controller.%t can divide a long bus into smaller %t can divide a long bus into smaller segments so that each segments so that each segmentsegment is is independentindependent trafficise.trafficise.The bridge uses a The bridge uses a table table to decide if the to decide if the frame needs to be forarded to another frame needs to be forarded to another segment.segment.With a bridge, With a bridge, to or more pairsto or more pairs of stations of stations can can communicate at the same timecommunicate at the same time..Brooks/Cole, 2003Bridges operate at the frst Bridges operate at the frst two layerstwo layers(physical layer and datalin! (physical layer and datalin! layer) of the OSI model.layer) of the OSI model. Note:Note:Brooks/Cole, 2003Figure 6-1-Swit&h.one kind of d/nami& 0ridgeBrooks/Cole, 2003Figure 6-11)outers in an internetBrooks/Cole, 2003Routers operate at the frst Routers operate at the frst three layersthree layers(physical" datalin!" and (physical" datalin!" and networ! layer)networ! layer)of the OSI model. of the OSI model. Note:Note:Brooks/Cole, 2003Whereas aWhereas a bridgebridge filters a frame based filters a frame based on the on the physical physical address of the frame, a address of the frame, a routerrouter routes a packet based on the routes a packet based on the logicallogical address of the packet.address of the packet.Whereas a Whereas a bridgebridge may connect may connect to to segments of a $"#segments of a $"#, a , a routerrouter can connect can connect to independent netorksto independent netorks..Brooks/Cole, 2003" " gateaygateay is a connecting device that is a connecting device that acts as a protocol converter.acts as a protocol converter." gateay is usually a computer" gateay is usually a computer installed installed ith the necessary softare.ith the necessary softare.Today the term Today the term gateaygateay is used is used interchangeably ith the terminterchangeably ith the term routerrouter. The . The distinction beteen the to terms is distinction beteen the to terms is disappearing.disappearing.Brooks/Cole, 2003Figure 6-12Conne&ting de'i&es and the OSI modelBrooks/Cole, 2003THE INTERNETTHE INTERNETANDANDTCP/IPTCP/IP6.56.5Brooks/Cole, 2003T)&T)&' Transmission control protocol ' Transmission control protocol *+&*+&' *ser datagram protocol' *ser datagram protocol %&%&' %nternet protocol' %nternet protocol,T&,T&' ,ile transfer protocol' ,ile transfer protocolS-T&S-T&' Simple mail transfer protocol' Simple mail transfer protocol&(&'&(&' &ost office protocol&ost office protocolHTT&HTT&' Hyperte.t transfer protocol' Hyperte.t transfer protocolFigure 6-13TC12I1 and OSI modelBrooks/Cole, 2003Figure 6-14I1 addresses in dotted-de&imal notationBrooks/Cole, 2003Figure 6-1"Client-ser'er modelBrooks/Cole, 2003)lient')lient' an application program running on an application program running on a local machinea local machineServer'Server' an application program running an application program running on a remote machineon a remote machine" client re/uests a service from a server." client re/uests a service from a server.The server program is alays running, The server program is alays running, and the client program runs only hen and the client program runs only hen needed.needed.Brooks/Cole, 2003Figure 6-16FT1Brooks/Cole, 2003,T& as designed to resolve to ,T& as designed to resolve to problems'problems'+ifferent coding systems in use+ifferent coding systems in use(ne machine may use "S)%%, and other may use(ne machine may use "S)%%, and other may use *nicode *nicode+ifferent file formats in use+ifferent file formats in useBrooks/Cole, 2003Figure 6-1%S#T121O1Brooks/Cole, 2003Figure 6-1(3mail addressviolet0ice.ntnu.edu.tBrooks/Cole, 2003Figure 6-1+T3L!3T-- a general client#serer model a general client#serer model$ocal login v.s. remote login$ocal login v.s. remote loginT1$#1T is a general client2server program on T1$#1T is a general client2server program on the %nternet that allo remote loginthe %nternet that allo remote loginBrooks/Cole, 2003Figure 6-2-4)Lhttp'33.ice.ntnu.edu.t34violetftp'33567.588.99.585*!$' *niform resource locator*!$' *niform resource locator" special kind of addressing using by HTT&" special kind of addressing using by HTT&Brooks/Cole, 2003WWW' World ide ebWWW' World ide ebHyperte.t' home pageHyperte.t' home pageBroserBroser+ocument Types+ocument TypesStatic documentsStatic documents +ynamic documents +ynamic documents"ctive documents "ctive documentsBrooks/Cole, 2003Figure 6-21,rowserBrooks/Cole, 2003Figure 6-22Categories of $e0 do&umentsStatic documents Static documents HT-$' Hyperte.t -arkup $anguage HT-$' Hyperte.t -arkup $anguage+ynamic documents+ynamic documents):%' )ommon :ateay %nterface (&erl) ):%' )ommon :ateay %nterface (&erl)"ctive documents"ctive documents;ava language ;ava languageBrooks/Cole, 2003"ctive document "ctive document"pplication layer "pplication layerBridge BridgeBroser BroserBus topology Bus topology)lient )lient)lient2server model )lient2server model)omputer netork )omputer netork)onnecting devices )onnecting devices+ata2link layer +ata2link layer+otted2decimal notation +otted2decimal notation+ynamic document +ynamic document1mail 1mailHT-$ HT-$HTT& HTT&%nternet %nternet%nternet address %nternet address%nternetork %nternetork%nternet protocol (%&) %nternet protocol (%&)%& address %& address$"# $"#$ical login $ical login-"# -"#-odel -odel#etork layer #etork layerBrooks/Cole, 2003#ode #ode#ode2to2node delivery #ode2to2node delivery(S% (S%&hysical address &hysical address&hysical layer &hysical layer&resentation layer &resentation layer&rotocol&rotocol !emote login!emote login !epeater !epeater!ing topology !ing topology!outer !outerSegment SegmentServer ServerSession layer Session layerS-T& S-T&Source2to2destination delivery Source2to2destination deliveryStar topologyStar topology Static document Static documentSitch SitchSynchroni