网络交换的基本概念ppt课件.ppt

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1、SwitchingConceptBridge/SwitchApplicationPresentationSessionTransportNetworkDataLinkPhysicalApplicationPresentationSessionTransportNetworkDataLinkPhysicalBridgesworkatlayer2oftheOSImodelTheirprimaryfunctionistorelayframeBridgePhysicalDataLinkPhysicalDataLinkBridge/SwitchMACLaye

2、rdevicesProtocolIndependentInterconnecttwoormoreLANsProcessreceivedframesbasedontheMACaddressesAddressedLearning,FramesFiltering&ForwardingFunctionIncreasethetotalthroughputofaLANEthernetFrameEthernetIIFrame816624IEEE802.3Frame(0800)IP(0806)ARP(8137)IPX(809B)AppleTalkPreambleD

3、ESTMACSRCMACTypeDATACRC64-151872-1526PreambleDESTMACSRCMACTypeDATACRCSFDLengthDSAPSSAPCtrl111or2802.2LLC42-1497High-levelInformationSFD:StartFrameDelimiterMACAddressFormatOctet012345BinaryRepresentation

4、00000000

5、00001000

6、01011010

7、00000000

8、00010010

9、00000001

10、HexIllustration00-10

11、-B5-00-48-80OUIManufacturer’sassignExamples:Accton00-00-E800-10-B5SMC00-E0-29(OrganizationallyUniqueIdentifier,OUI)UniqueaddressforidentifyForwardingRate86667uslantencyEthernetmin.64-byteframes(64+8)X8=576bits57us(min.frametime)+9.6us(inter-framegap)=67us/frameFramescanarrivee

12、very67usMaximumthroughputforEthernet(64+8)X8+96=672bits10Mbps/672=14880frame/sec(pps)IffastEthernet(100Mbps),then148,800frame/secppsPreambleDESTSRCTypeDATACRCPreambleDESTSRCTypeDATACRC48-150248-15028664ForwardingOptionDAisreceived64bytesisreceivedwholeframeisreceivedCut-throug

13、hFragment-freeStore-and-forwardThefirstbitsintheframecanbesentouttheoutboundportbeforethefinalbitsintheincomingframearereceived,anditdoesnotdiscardframethatfailtheCRCcheck.EnsuringthatcollisionfragmentsarenotpropagatedthroughthenetworkCRCandRuntcheckEnsuringthatonlygoodframesa

14、repassedtotheirdestinationSwitchingArchitectureFilteringDatabaseLookupForwardingtothisPortFiltering(discard)NOYESFloodingtoallotherportsDAisUnicast?RXPort=PortID?ReceiveaFrameYESNODA:DestinationAddressFind?YESNOLearningDASADataFCSXX-XX-XX-XX-XX-XX00-1C-CF-0D-15-BFPC100-1C-CF-0

15、D-15-BFMACAddressPort00-1C-CF-00-15-BF1112424FloodingDASAData