COMPUTERNETWORKSChapter11AsynchronousTransferModeProtocolArchitectureUserplaneProvidesforuserinformationtransferControlplaneCallandconnectioncontrolManagementplanePlanemanagementwholesystemfunctionsLayermanagementResourcesandparametersinprotocolentitiesSimilaritiesbetweenATMandpacketswitchingTransferofdataindiscretechunksMultiplelogicalconnectionsoversinglephysicalinterfaceInATMflowoneachlogicalconnectionisinfixedsizedpacketscalledcellsMinimalerrorandflowcontrolReducedoverheadDatarates(physicallayer)25.6Mbpsto622.08MbpsATMLogicalConnectionsVirtualchannelconnections(VCC虛通路)AnalogoustovirtualcircuitinX.25BasicunitofswitchingBetweentwoendusersFullduplexFixedsizecellsuser-networkexchange(control)andnetwork-networkexchange(networkmanagementandrouting)Virtualpathconnection(VPC虛通道)BundleofVCCwithsameendpointsAdvantagesSimplifiednetworkarchitectureIncreasednetworkperformanceandreliabilityReducedprocessingShortconnectionsetuptimeEnhancednetworkservicesUsingofVPUsingofVCCallestablishmentusingVPBetweenendusersEndtoenduserdataControlsignalsVPCprovidesoverallcapacityVCCorganizationdonebyusersBetweenenduserandnetworkControlsignalingBetweennetworkentitiesNetworktrafficmanagementRoutingVC/VPCharacteristicsQualityofserviceSwitchedandsemi-permanentchannelconnectionsCallsequenceintegrityguaranteeTrafficparameternegotiationandusagemonitoringCharacteristicsofVPConlySomevirtualchannelidentifiersareleftfornetworkuse(networkmanagement)VCC/VPCSetupVCCSemi-permanentVCCUsertouserswitchingnosignalingrequiredMeta-signalingchannelUsedaspermanentcontrolsignalchanneltosetupcallcontrolchannelUsertonetworksignalingvirtualchannelForcontrolsignalingUsedtosetupVCCstocarryuserdataUsertousersignalingvirtualchannelWithinpre-establishedVPCUsedbytwoenduserswithoutnetworkinterventiontoestablishandreleaseusertouserVCCVPCSemi-permanentCustomercontrolledSetupbycontrolsignalingVCCNetworkcontrolledATMCellsFixedsize5octetheader48octetinformationfieldSmallcellsreducequeuingdelayforhighprioritycellsSmallcellscanbeswitchedmoreefficientlyEasiertoimplementswitchingofsmallcellsinhardwareGenericflowcontrolOnlyatusertonetworkinterfaceControlsflowonlyatthispointVirtualpathidentifierVirtualchannelidentifierPayloadtypee.g.userinfoornetworkmanagementCelllosspriorityHeadererrorcontrolGenericFlowControl(GFC)Controltrafficflowatusertonetworkinterface(UNI)toalleviateshorttermoverloadTwosetsofproceduresUncontrolledtransmissionControlledtransmissionEveryconnectioneithersubjecttoflowcontrolornotSubjecttoflowcontrolMaybeonegroup(A)defaultMaybetwogroups(AandB)FlowcontrolisfromsubscribertonetworkSingleGroupofConnections(1)Terminalequipment(TE)initializestwovariablesTRANSMITflagto1GO_CNTR(creditcounter)to0GO_VALUEto1orlargerIfTRANSMIT=1cellsonuncontrolledconnectionmaybesentanytimeIfTRANSMIT=0nocellsmaybesent(oncontrolledoruncontrolledconnections)IfHALTreceived,TRANSMITsetto0andremainsuntilNO_HALTUseofHALT:TolimiteffectivedatarateonATMToreducedataratebyhalf,HALTissuedtobeineffect50%oftimeDoneonregularpatternoverlifetimeofconnectionSingleGroupofConnections(2)IfTRANSMIT=1andnocelltotransmitonanyuncontrolledconnection:IfGO_CNTR>0,TEmaysendcelloncontrolledconnectionCellmarkedasbeingoncontrolledconnectionGO_CNTRdecrementedIfGO_CNTR=0,TEmaynotsendoncontrolledconnectionTEsetsGO_CNTRtoGO_VALUEuponreceivingSETsignalNullsignalhasnoeffectSeeTable11.3TwoQueueModelTwocountersGO_CNTR_A,GO_VALUE_A,GO_CNTR_B,GO_VALUE_BHeaderErrorControl8biterrorcontrolfieldCalculatedonremaining32bitsofheaderAllowssomeerrorcorrectionEffectofErrorinCellHeaderTransmissionofATMCells622.08Mbps155.52Mbps51.84Mbps25.6MbpsCellBasedphysicallayerSDHbasedphysicallayerCellBasedPhysicalLayerNoframingimposedContinuousstreamof53octetcellsCelldelineationbasedonheadererrorcontrolfieldImpactofRandomBitErrorsonCellDelineationPerformance維持同步的時(shí)間AcquisitionTimevsBitErrorRate建立同步的時(shí)間SDHBasedPhysicalLayerImposesstructureonATMstreame.g.for155.52MbpsUseSTM-1(STS-3)frameCancarryATMandSTMpayloadsSpecificconnectionscanbecircuitswitchedusingSDHchannelSDHmultiplexingtechniquescancombineseveralATMstreamsATMServiceCategoriesRealtimeConstantbitrate(CBR)Realtimevariablebitrate(rt-VBR)Non-realtimeNon-realtimevariablebitrate(nrt-VBR)Availablebitrate(ABR)Unspecifiedbitrate(UBR)Guaranteedframerate(GFR)CBRFixeddataratecontinuouslyavailableTightupperboundondelaypressedaudioandvideoVideoconferencingInteractiveaudioA/Vdistributionandretrievalrt-VBRTimesensitiveapplicationTightlyconstraineddelayanddelayvariationrt-VBRapplicationstransmitataratethatvarieswithtimee.g.compressedvideoProducesvaryingsizedimageframesOriginal(pressed)framerateconstantSocompresseddataratevariesCanstatisticallymultiplexconnectionsnrt-VBRMaybeabletocharacterizeexpectedtrafficflowImproveQoSinlossanddelayEndsystemspecifies:PeakcellrateSustainableoraveragerateMeasureofhowburstytrafficise.g.Airlinereservations,bankingtransactionsUBRMaybeadditionalcapacityoverandabovethatusedbyCBRandVBRtrafficNotallresourcesdedicatedBurstynatureofVBRForapplicationthatcantoleratesomecelllossorvariabledelayse.g.TCPbasedtrafficCellsforwardedonFIFObasisBesteffortsserviceABRApplicationspecifiespeakcellrate(PCR)andminimumcellrate(MCR)ResourcesallocatedtogiveatleastMCRSparecapacitysharedamongallABRsourcese.g.LANinterconnectionGuaranteedFrameRate(GFR)DesignedtosupportIPbackbonesubnetworksBetterservicethanUBRforframebasedtrafficIncludingIPandEthernetGFRbetteralternativefortrafficoriginatingonEthernetNetworkawareofframe/packetboundariesWhencongested,allcellsfromframediscardedGuaranteedminimumcapacityAdditionalframescarriedofnotcongestedATMBitRateServicesATMAdaptationLayerSupportforinformationtransferprotocolnotbasedonATMPCM(voice)AssemblebitsintocellsRe-assembleintoconstantflowIPMapIPpacketsontoATMcellsFragmentIPpacketsUseLAPFoverATMtoretainallIPinfrastructureAALServicesHandletransmissionerrorsSegmentationandre-assemblyHandlelostandmisinsertedcellsFlowcontrolandtimingSupportedApplicationtypesCircuitemulationVBRvoiceandvideoGeneraldataserviceIPoverATMMultiprotocolencapsulationoverATM(MPOA)IPX,AppleTalk,DECNET)LANemulationAALProtocolsConvergencesublayer(CS)SupportforspecificapplicationsAALuserattachesatSAPSegmentationandre-assemblysublayer(SAR)PackagesandunpacksinforeceivedfromCSintocellsFourtypesType1Type2Type3/4Type5SARPDUAALType1,2AALType1CBRsourceNodefinitionofCSPDUSN:1bitCSI+3bitSequenceCountOddcount:for1,3,5,7SARPDU,4bitsprovideclockEvencount:for0,2,4,6SARPDU,every2SARPDUSconstituteanentitySNP:3bitCRC+1bitParityCheckAALType2VBRAnalogapplicati