无线通信网络-第14章 IEEE 802.11无线局域网标准课件.ppt

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1、IEEE802.11WirelessLANStandardChapter14IEEE802ProtocolLayersProtocolArchitectureFunctionsofphysicallayer:Encoding/decodingofsignalsPreamblegeneration/removal(forsynchronization)Bittransmission/receptionIncludesspecificationofthetransmissionmediumProtoc

2、olArchitectureFunctionsofmediumaccesscontrol(MAC)layer:Ontransmission,assembledataintoaframewithaddressanderrordetectionfieldsOnreception,disassembleframeandperformaddressrecognitionanderrordetectionGovernaccesstotheLANtransmissionmediumFunctionsoflog

3、icallinkcontrol(LLC)Layer:ProvideaninterfacetohigherlayersandperformflowanderrorcontrolSeparationofLLCandMACThelogicrequiredtomanageaccesstoashared-accessmediumnotfoundintraditionallayer2datalinkcontrolForthesameLLC,severalMACoptionsmaybeprovidedMACFr

4、ameFormatMACcontrolContainsMacprotocolinformationDestinationMACaddressDestinationphysicalattachmentpointSourceMACaddressSourcephysicalattachmentpointCRCCyclicredundancycheckLogicalLinkControlCharacteristicsofLLCnotsharedbyothercontrolprotocols:Mustsup

5、portmultiaccess,shared-mediumnatureofthelinkRelievedofsomedetailsoflinkaccessbyMAClayerLLCServicesUnacknowledgedconnectionlessserviceNoflow-anderror-controlmechanismsDatadeliverynotguaranteedConnection-modeserviceLogicalconnectionsetupbetweentwousersF

6、low-anderror-controlprovidedAcknowledgedconnectionlessserviceCrossbetweenprevioustwoDatagramsacknowledgedNopriorlogicalsetupDifferencesbetweenLLCandHDLCLLCusesasynchronousbalancedmodeofoperationofHDLC(type2operation)LLCsupportsunacknowledgedconnection

7、lessservice(type1operation)LLCsupportsacknowledgedconnectionlessservice(type3operation)LLCpermitsmultiplexingbytheuseofLLCserviceaccesspoints(LSAPs)IEEE802.11ArchitectureDistributionsystem(DS)Accesspoint(AP)Basicserviceset(BSS)Stationscompetingforacce

8、sstosharedwirelessmediumIsolatedorconnectedtobackboneDSthroughAPExtendedserviceset(ESS)TwoormorebasicservicesetsinterconnectedbyDSIEEE802.11ServicesDistributionofMessagesWithinaDSDistributionserviceUsedtoexchangeMACframesfromstationinoneBSStos