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CommunicationNetworksChapter3CommunicationNetworksChapter1TypesofCommunicationNetworksTraditionalTraditionallocalareanetwork(LAN)Traditionalwideareanetwork(WAN)Higher-speedHigh-speedlocalareanetwork(LAN)Metropolitanareanetwork(MAN)High-speedwideareanetwork(WAN)TypesofCommunicationNetworkSpeedandDistanceofCommunicationsNetworksSpeedandDistanceofCommunicCharacteristicsofWANsCoverslargegeographicalareasCircuitsprovidedbyacommoncarrierConsistsofinterconnectedswitchingnodesTraditionalWANsprovidemodestcapacity64000bpscommonBusinesssubscribersusingT-1service–1.544MbpscommonHigher-speedWANsuseopticalfiberandtransmissiontechniqueknownasasynchronoustransfermode(ATM)10sand100sofMbpscommonCharacteristicsofWANsCoversCharacteristicsofLANsLikeWAN,LANinterconnectsavarietyofdevicesandprovidesameansforinformationexchangeamongthemTraditionalLANsProvidedataratesof1to20MbpsHigh-speedLANSProvidedataratesof100Mbpsto1Gbps
CharacteristicsofLANsLikeWADifferencesbetweenLANsandWANsScopeofaLANissmallerLANinterconnectsdeviceswithinasinglebuildingorclusterofbuildingsLANusuallyownedbyorganizationthatownstheattacheddevicesForWANs,mostofnetworkassetsarenotownedbysameorganizationInternaldatarateofLANismuchgreaterDifferencesbetweenLANsandWTheNeedforMANsTraditionalpoint-to-pointandswitchednetworktechniquesusedinWANsareinadequateforgrowingneedsoforganizationsNeedforhighcapacityandlowcostsoverlargeareaMANprovides:ServicetocustomersinmetropolitanareasRequiredcapacityLowercostandgreaterefficiencythanequivalentservicefromtelephonecompany
TheNeedforMANsTraditionalpSwitchingTermsSwitchingNodes:IntermediateswitchingdevicethatmovesdataNotconcernedwithcontentofdataStations:EnddevicesthatwishtocommunicateEachstationisconnectedtoaswitchingnodeCommunicationsNetwork:Acollectionofswitchingnodes
SwitchingTermsSwitchingNodesSwitchedNetworkSwitchedNetworkObservationsofFigure3.3
Somenodesconnectonlytoothernodes(e.g.,5and7)SomenodesconnecttooneormorestationsNode-stationlinksusuallydedicatedpoint-to-pointlinksNode-nodelinksusuallymultiplexedlinksFrequency-divisionmultiplexing(FDM)Time-divisionmultiplexing(TDM)Notadirectlinkbetweeneverynodepair
ObservationsofFigure3.3SomTechniquesUsedinSwitchedNetworksCircuitswitchingDedicatedcommunicationspathbetweentwostationsE.g.,publictelephonenetworkPacketswitchingMessageisbrokenintoaseriesofpacketsEachnodedeterminesnextlegoftransmissionforeachpacketTechniquesUsedinSwitchedNePhasesofCircuitSwitchingCircuitestablishmentAnendtoendcircuitisestablishedthroughswitchingnodesInformationTransferInformationtransmittedthroughthenetworkDatamaybeanalogvoice,digitizedvoice,orbinarydataCircuitdisconnectCircuitisterminatedEachnodedeallocatesdedicatedresourcesPhasesofCircuitSwitchingCirCharacteristicsofCircuitSwitchingCanbeinefficientChannelcapacitydedicatedfordurationofconnectionUtilizationnot100%DelaypriortosignaltransferforestablishmentOnceestablished,networkistransparenttousersInformationtransmittedatfixeddataratewithonlypropagationdelay
CharacteristicsofCircuitSwiComponentsofPublicTelecommunicationsNetworkSubscribers-devicesthatattachtothenetwork;mostlytelephonesSubscriberline-linkbetweensubscriberandnetworkAlsocalledsubscriberlooporlocalloopExchanges-switchingcentersinthenetworkAswitchingcentersthatsupportsubscribersisanendofficeTrunks-branchesbetweenexchanges
ComponentsofPublicTelecommuHowPacketSwitchingWorks
Dataistransmittedinblocks,calledpacketsBeforesending,themessageisbrokenintoaseriesofpacketsTypicalpacketlengthis1000octets(bytes)PacketsconsistsofaportionofdataplusapacketheaderthatincludescontrolinformationAteachnodeenroute,packetisreceived,storedbrieflyandpassedtothenextnode
HowPacketSwitchingWorksDatPacketSwitchingPacketSwitchingPacketSwitchingPacketSwitchingPacketSwitchingAdvantagesLineefficiencyisgreaterManypacketsovertimecandynamicallysharethesamenodetonodelinkPacket-switchingnetworkscancarryoutdata-rateconversionTwostationswithdifferentdataratescanexchangeinformationUnlikecircuit-switchingnetworksthatblockcallswhentrafficisheavy,packet-switchingstillacceptspackets,butwithincreaseddeliverydelayPrioritiescanbeusedPacketSwitchingAdvantagesLinDisadvantagesofPacketSwitchingEachpacketswitchingnodeintroducesadelayOverallpacketdelaycanvarysubstantiallyThisisreferredtoasjitterCausedbydifferingpacketsizes,routestakenandvaryingdelayintheswitchesEachpacketrequiresoverheadinformationIncludesdestinationandsequencinginformationReducescommunicationcapacityMoreprocessingrequiredateachnode
DisadvantagesofPacketSwitchPacketSwitchingNetworks-DatagramEachpackettreatedindependently,withoutreferencetopreviouspacketsEachnodechoosesnextnodeonpacket’spathPacketsdon’tnecessarilyfollowsamerouteandmayarriveoutofsequenceExitnoderestorespacketstooriginalorderResponsibilityofexitnodeordestinationtodetectlossofpacketandhowtorecover
PacketSwitchingNetworks-DaPacketSwitchingNetworks–DatagramAdvantages:CallsetupphaseisavoidedBecauseit’smoreprimitive,it’smoreflexibleDatagramdeliveryismorereliablePacketSwitchingNetworks–DaPacketSwitchingNetworks–VirtualCircuitPreplannedrouteestablishedbeforepacketssentAllpacketsbetweensourceanddestinationfollowthisrouteRoutingdecisionnotrequiredbynodesforeachpacketEmulatesacircuitinacircuitswitchingnetworkbutisnotadedicatedpathPacketsstillbufferedateachnodeandqueuedforoutputoveralinePacketSwitchingNetworks–ViPacketSwitchingNetworks–VirtualCircuitAdvantages:PacketsarriveinoriginalorderPacketsarrivecorrectlyPacketstransmittedmorerapidlywithoutroutingdecisionsmadeateachnodePacketSwitchingNetworks–ViEffectofPacketSizeonTransmissionEffectofPacketSizeonTransEffectofPacketSizeonTransmission
BreakinguppacketsdecreasestransmissiontimebecausetransmissionisallowedtooverlapFigure3.9aEntiremessage(40octets)+headerinformation(3octets)sentatonceTransmissiontime:129octet-timesFigure3.9bMessagebrokeninto2packets(20octets)+header(3octets)Transmissiontime:92octet-times
EffectofPacketSizeonTransEffectofPacketSizeonTransmissionFigure3.9cMessagebrokeninto5packets(8octets)+header(3octets)Transmissiontime:77octet-timesFigure3.9dMakingthepacketstoosmall,transmissiontimestartsincreasesEachpacketrequiresafixedheader;themorepackets,themoreheadersEffectofPacketSizeonTransAsynchronousTransferMode(ATM)AlsoknownascellrelayOperatesathighdataratesResemblespacketswitchingInvolvestransferofdataindiscretechunks,likepacketswitchingAllowsmultiplelogicalconnectionstobemultiplexedoverasinglephysicalinterfaceMinimalerrorandflowcontrolcapabilitiesreducesoverheadprocessingandsizeFixed-sizecellssimplifyprocessingatATMnodes
AsynchronousTransferMode(ATATMTerminologyVirtualchannelconnection(VCC)LogicalconnectioninATMBasicunitofswitchinginATMnetworkAnalogoustoavirtualcircuitinpacketswitchingnetworksExchangesvariable-rate,full-duplexflowoffixed-sizecellsVirtualpathconnection(VPC)BundleofVCCsthathavethesameendpoints
ATMTerminologyVirtualchannelAdvantagesofVirtualPathsSimplifiednetworkarchitectureIncreasednetworkperformanceandreliabilityReducedprocessingandshortconnectionsetuptimeEnhancednetworkservicesAdvantagesofVirtualPathsSimCallEstablishmentCallEstablishmentVirtualChannelConnectionUses
BetweenendusersCancarryend-to-enduserdataorcontrolsignalingbetweentwousersBetweenanenduserandanetworkentityUsedforuser-to-networkcontrolsignalingBetweentwonetworkentitiesUsedfornetworktrafficmanagementandroutingfunctionsVirtualChannelConnectionUseVirtualPath/VirtualChannelCharacteristicsQualityofserviceSpecifiedbyparameterssuchascelllossratioandcelldelayvariationSwitchedandsemipermanentvirtualchannelconnectionsCellsequenceintegrityTrafficparameternegotiationandusagemonitoringVirtualchannelidentifierrestrictionwithinaVPCVirtualPath/VirtualChannelCATMCellHeaderFormatGenericflowcontrol(GFC)–4bits,usedonlyinuser-networkinterfaceUsedtoalleviateshort-termoverloadconditionsinnetworkVirtualpathidentifier(VPI)–8bitsattheuser-networkinterface,12bitsatnetwork-networkinterfaceRoutingfieldVirtualchannelidentifier(VCI)–8bitsUsedforroutingtoandfromenduserATMCellHeaderFormatGenericATMCellHeaderFormatPayloadtype(PT)–3bitsIndicatestypeofinformationininformationfieldCelllosspriority(CLP)–1bitProvidesguidancetonetworkintheeventofcongestionHeadererrorcontrol(HEC)–8bitErrorcodeATMCellHeaderFormatPayloadATMServiceCategoriesReal-timeserviceConstantbitrate(CBR)Real-timevariablebitrate(rt-VBR)Non-real-timeserviceNon-real-timevariablebitrate(nrt-VBR)Availablebitrate(ABR)Unspecifiedbitrate(UBR)ATMServiceCategoriesReal-timExamplesofCBRApplicationsVideoconferencingInteractiveaudio(e.g.,telephony)Audio/videodistribution(e.g.,television,distancelearning,pay-per-view)Audio/videoretrieval(e.g.,video-on-demand,audiolibrary)ExamplesofCBRApplicationsViExamplesofUBRapplicationsText/data/imagetransfer,messaging,distribution,retrievalRemoteterminal(e.g.,telecommuting)
ExamplesofUBRapplicationsTeCommunicationNetworksChapter3CommunicationNetworksChapter38TypesofCommunicationNetworksTraditionalTraditionallocalareanetwork(LAN)Traditionalwideareanetwork(WAN)Higher-speedHigh-speedlocalareanetwork(LAN)Metropolitanareanetwork(MAN)High-speedwideareanetwork(WAN)TypesofCommunicationNetworkSpeedandDistanceofCommunicationsNetworksSpeedandDistanceofCommunicCharacteristicsofWANsCoverslargegeographicalareasCircuitsprovidedbyacommoncarrierConsistsofinterconnectedswitchingnodesTraditionalWANsprovidemodestcapacity64000bpscommonBusinesssubscribersusingT-1service–1.544MbpscommonHigher-speedWANsuseopticalfiberandtransmissiontechniqueknownasasynchronoustransfermode(ATM)10sand100sofMbpscommonCharacteristicsofWANsCoversCharacteristicsofLANsLikeWAN,LANinterconnectsavarietyofdevicesandprovidesameansforinformationexchangeamongthemTraditionalLANsProvidedataratesof1to20MbpsHigh-speedLANSProvidedataratesof100Mbpsto1Gbps
CharacteristicsofLANsLikeWADifferencesbetweenLANsandWANsScopeofaLANissmallerLANinterconnectsdeviceswithinasinglebuildingorclusterofbuildingsLANusuallyownedbyorganizationthatownstheattacheddevicesForWANs,mostofnetworkassetsarenotownedbysameorganizationInternaldatarateofLANismuchgreaterDifferencesbetweenLANsandWTheNeedforMANsTraditionalpoint-to-pointandswitchednetworktechniquesusedinWANsareinadequateforgrowingneedsoforganizationsNeedforhighcapacityandlowcostsoverlargeareaMANprovides:ServicetocustomersinmetropolitanareasRequiredcapacityLowercostandgreaterefficiencythanequivalentservicefromtelephonecompany
TheNeedforMANsTraditionalpSwitchingTermsSwitchingNodes:IntermediateswitchingdevicethatmovesdataNotconcernedwithcontentofdataStations:EnddevicesthatwishtocommunicateEachstationisconnectedtoaswitchingnodeCommunicationsNetwork:Acollectionofswitchingnodes
SwitchingTermsSwitchingNodesSwitchedNetworkSwitchedNetworkObservationsofFigure3.3
Somenodesconnectonlytoothernodes(e.g.,5and7)SomenodesconnecttooneormorestationsNode-stationlinksusuallydedicatedpoint-to-pointlinksNode-nodelinksusuallymultiplexedlinksFrequency-divisionmultiplexing(FDM)Time-divisionmultiplexing(TDM)Notadirectlinkbetweeneverynodepair
ObservationsofFigure3.3SomTechniquesUsedinSwitchedNetworksCircuitswitchingDedicatedcommunicationspathbetweentwostationsE.g.,publictelephonenetworkPacketswitchingMessageisbrokenintoaseriesofpacketsEachnodedeterminesnextlegoftransmissionforeachpacketTechniquesUsedinSwitchedNePhasesofCircuitSwitchingCircuitestablishmentAnendtoendcircuitisestablishedthroughswitchingnodesInformationTransferInformationtransmittedthroughthenetworkDatamaybeanalogvoice,digitizedvoice,orbinarydataCircuitdisconnectCircuitisterminatedEachnodedeallocatesdedicatedresourcesPhasesofCircuitSwitchingCirCharacteristicsofCircuitSwitchingCanbeinefficientChannelcapacitydedicatedfordurationofconnectionUtilizationnot100%DelaypriortosignaltransferforestablishmentOnceestablished,networkistransparenttousersInformationtransmittedatfixeddataratewithonlypropagationdelay
CharacteristicsofCircuitSwiComponentsofPublicTelecommunicationsNetworkSubscribers-devicesthatattachtothenetwork;mostlytelephonesSubscriberline-linkbetweensubscriberandnetworkAlsocalledsubscriberlooporlocalloopExchanges-switchingcentersinthenetworkAswitchingcentersthatsupportsubscribersisanendofficeTrunks-branchesbetweenexchanges
ComponentsofPublicTelecommuHowPacketSwitchingWorks
Dataistransmittedinblocks,calledpacketsBeforesending,themessageisbrokenintoaseriesofpacketsTypicalpacketlengthis1000octets(bytes)PacketsconsistsofaportionofdataplusapacketheaderthatincludescontrolinformationAteachnodeenroute,packetisreceived,storedbrieflyandpassedtothenextnode
HowPacketSwitchingWorksDatPacketSwitchingPacketSwitchingPacketSwitchingPacketSwitchingPacketSwitchingAdvantagesLineefficiencyisgreaterManypacketsovertimecandynamicallysharethesamenodetonodelinkPacket-switchingnetworkscancarryoutdata-rateconversionTwostationswithdifferentdataratescanexchangeinformationUnlikecircuit-switchingnetworksthatblockcallswhentrafficisheavy,packet-switchingstillacceptspackets,butwithincreaseddeliverydelayPrioritiescanbeusedPacketSwitchingAdvantagesLinDisadvantagesofPacketSwitchingEachpacketswitchingnodeintroducesadelayOverallpacketdelaycanvarysubstantiallyThisisreferredtoasjitterCausedbydifferingpacketsizes,routestakenandvaryingdelayintheswitchesEachpacketrequiresoverheadinformationIncludesdestinationandsequencinginformationReducescommunicationcapacityMoreprocessingrequiredateachnode
DisadvantagesofPacketSwitchPacketSwitchingNetworks-DatagramEachpackettreatedindependently,withoutreferencetopreviouspacketsEachnodechoosesnextnodeonpacket’spathPacketsdon’tnecessarilyfollowsamerouteandmayarriveoutofsequenceExitnoderestorespacketstooriginalorderResponsibilityofexitnodeordestinationtodetectlossofpacketandhowtorecover
PacketSwitchingNetworks-DaPacketSwitchingNetworks–DatagramAdvantages:CallsetupphaseisavoidedBecauseit’smoreprimitive,it’smoreflexibleDatagramdeliveryismorereliablePacketSwitchingNetworks–DaPacketSwitchingNetworks–VirtualCircuitPreplannedrouteestablishedbeforepacketssentAllpacketsbetweensourceanddestinationfollowthisrouteRoutingdecisionnotrequiredbynodesforeachpacketEmulatesacircuitinacircuitswitchingnetworkbutisnotadedicatedpathPacketsstillbufferedateachnodeandqueuedforoutputoveralinePacketSwitchingNetworks–ViPacketSwitchingNetworks–VirtualCircuitAdvantages:PacketsarriveinoriginalorderPacketsarrivecorrectlyPacketstransmittedmorerapidlywithoutroutingdecisionsmadeateachnodePacketSwitchingNetworks–ViEffectofPacketSizeonTransmissionEffectofPacketSizeonTransEffectofPacketSizeonTransmission
BreakinguppacketsdecreasestransmissiontimebecausetransmissionisallowedtooverlapFigure3.9aEntiremessage(40octets)+headerinformation(3octets)sentatonceTransmissiontime:129octet-timesFigure3.9bMessagebrokeninto2packets(20octets)+header(3octets)Transmissiontime:92octet-times
EffectofPacketSizeonTransEffectofPacketSizeonTransmissionFigure3.9cMessagebrokeninto5packets(8octets)+header(3octets)Transmissiontime:77octet-timesFigure3.9dMakingthepacketstoosmall,transmissiontimestartsincreasesEachpacketrequiresafixedheader;themorepackets,themoreheadersEffectofPacketSizeonTransAsynchronousTransferMode(ATM)AlsoknownascellrelayOperatesathighdataratesResemblespacketswitchingInvolvestransferofdataindiscretechunks,likepacketswitchingAllowsmultiplelogicalconnectionstobemultiplexedoverasinglephysicalinterfaceMinimalerrorandflowcontrolcapabilitiesreducesoverheadprocessingandsizeFixed-sizecellssimplifyprocessingatATMnodes
AsynchronousTransferMode(ATATMTerminologyVirtualchannelconnection(VCC)LogicalconnectioninATMBasicunitofswitchinginATMnetworkAnalogoustoavirtualcircuitinpacketswitchingnetworksExchangesvariable-rate,full-duplexflowoffixed-sizecellsVirtualpathconnection(VPC)BundleofVCCsthathavethesameendpoints
ATMTerminologyVirtualchannelAdvantagesofVirtualPathsSimplifiednetworkarchitectureIncreasednetworkperformanceandreliabilityReducedprocessingandshortconnectionsetuptimeEnhancednetworkservicesAdvantagesofV
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