高级网络技术-Ethernet(思科教材)ppt课件.ppt

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1、EthernetObjectivesmediaaccesscontrolmethod（介质访问控制方法）usedbyEthernetprotocol.Layer2addressingEthernetswitchesvs.hubsOverviewofEthernetEthernet-StanderdsandImplementationThefirstEthernetstandardwaspublishedin1980byaconsortiumofDigitalEquipmentCorporation,Intel,andXerox(DIX).In1985,theIn

2、stituteofElectricalandElectronicsEngineers(IEEE)standardscommitteeforLocalandMetropolitanNetworkspublishedstandardsforLANs.ThestandardforEthernetis802.3.EthernetoperatesinthelowertwolayersoftheOSImodel:theoftheDataLinklayerandthePhysicallayer.Ethernet-Layer1andLayer2EthernetatLayer1i

3、nvolvessignaling,mediaandvarioustopologiesTheDataLinklayerisdividedintotwosublayersMediaAccessControl(MAC)sublayerLogicalLinkControl(LLC)sublayerPhysicalImplementationsofEthernetThesuccessofEthernetisduetothefollowingfactors:SimplicityandeaseofmaintenanceAbilitytoincorporatenewtechno

4、logiesReliabilityLowcostofinstallationandupgradeIntoday'snetworks,EthernetusesUTPcoppercablesandopticalfibertointerconnectnetworkdevicesviaintermediarydevicessuchashubsandswitches.HistoricEthernetThefirstversionsofEthernetusedcoaxialcabletoconnectcomputersinabustopology（总线型拓扑）.Thickn

5、et,(10BASE5)Thinnet(10BASE2)Nowthephysicaltopologywaschangedtoastartopology（星型拓扑）usinghubs.TheoriginalmediawerereplacedbyearlycategoriesofUTPcables（非屏蔽双绞线）.TheEthernetFrameandAddressingTheFrame–EncapsulatingthePacketTheEthernetframestructureaddsheadersandtrailersaroundtheLayer3PDUtoe

6、ncapsulatethemessagebeingsent.TherearetwostylesofEthernetframing:IEEE802.3(original)andtherevisedIEEE802.3(Ethernet).TheFrame–EncapsulatingthePacketThePreamble(7bytes)andStartFrameDelimiter(SFD)(1byte)fieldsareusedforsynchronizationbetweenthesendingandreceivingdevices.TheDestinationM

7、ACAddressfield(6bytes)istheidentifierfortheintendedrecipient.TheSourceMACAddressfield(6bytes)identifiestheframe'soriginatingNICorinterface.TheLength/Typefield(2bytes)definestheexactlengthoftheframe'sdatafield.TheDataandPadfields(46-1500bytes)containstheencapsulateddatafromahigherlaye

8、r,whichisage