ATM适配层.ppt

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1、RivierCollegeCS575:AdvancedLANsATMAdaptationLayerCS5751ATMAdaptationLayerATMAdaptationLayerFunctionsTheATMAdaptationLayer(AAL)isdesignedtosupportdifferenttypesofapplicationsanddifferenttypesoftraffic,suchasvoice,video,imagery,anddataItsbasicfunctionistheenhancedadapta

2、tionofservicesprovidedbytheATMlayertotherequirementsofthehigherlayerItmapshigherlayerPDUsintotheinformationfieldoftheATMcellAALisdividedintotheConvergenceSublayer(CS)andtheSegmentationandReassembly(SAR)SublayerTheConvergenceSublayerisservicedependentandprovidestheAALse

3、rvicesattheAAL-SAPThefunctionsoftheSARsublayeraresegmentationofhigherlayerPDUsintoasuitablesizefortheinformationfieldoftheATMcell(48octets)atthetransmittingendandreassemblyoftheinformationfieldsintohigherlayerPDUsatthereceivingendCS5752ATMAdaptationLayerATMAdaptationSu

4、blayersConvergenceSublayer(CS):Handlinglost/misdeliveredcellsTimingrecoveryInterleavingSegmentationandReassemblySublayer(SAR):Splitframes/bitstreamintocellsfortransmissionReassembleframes/bitstreamforreceivingSupportmultipleprotocolsHigherLayersATMAdaptationLayer(AAL)C

5、onvergenceSublayer(CS)SegmentationandReassemblySublayer(SAR)ATMLayer(ATM)VirtualChannel(VC)VirtualPath(VP)PhysicalLayer(PL)TransmissionConvergenceSublayer(TC)PhysicalMediumSublayer(PM)CS5753ATMAdaptationLayerAALProtocolsandServiceClassesTominimizethenumberofAALprotocol

6、s,ITU-TproposedaserviceclassificationspecifictotheAALTheclassificationwasmadewithrespecttothefollowingparameters:TimingrelationshipbetweensenderandreceiverRelatedNotrelatedBitrateConstantbitrateVariablebitrateConnectionmodeConnection-orientedConnectionlessCS5754ATMAdap

7、tationLayerAALProtocolsandServiceClasses(Concluded)FourAALprotocolshavebeendefinedtosupportfourAALserviceclassesAALserviceclassesClassAClassBClassCClassDAALprotocolsAAL1AAL2AAL3/4AAL5CS5755ATMAdaptationLayerAALServicesConnectionlessDateTransferBitRateConnectionModeExam

8、plesofServicesCircuitEmulationConstantBitRateVideoandAudioConstantVariableConnectionOrientedConnectionlessVariableBit