Ender204426777乾颐堂CCNAv3.0课程InterconnectingCiscoNetworkingDevices,Part2(ICND2)v3.0Wide-AreaNetworks乾颐堂CCNAv3.0Ender204426777IntroductiontoWANTechnologies5-3Ender。ISISIntroductiontoWANTechnologies(Cont.)5-4Ender。ISISWANDevices•Routers–CSU/DSU（ChannelServiceUnit，通道服务单元：把终端用户和本地数字电话环路相连的数字接口设备；DataServiceUnit，数据服务单元：指的是用于数字传输中的一种设备，它能够把DTE设备上的物理层接口适配到T1或者E1等通信设施上。）•WANswitches•Corerouters•Modems5-5Ender。ISISWANDevices(Cont.)5-6Ender。ISISSerialWANCabling5-7Ender。ISISWANLayer2Protocols5-8Ender。ISISWANLinkOptions5-9Ender。ISISWANLinkOptions(Cont.)5-10Ender。ISISSummary•TherearethreemajorcharacteristicsofaWAN:–Connectionofdevicesthatareseparatedbywidegeographicaldistances–Useoftheservicesofcarrierssuchastelcos,cablecompanies,satellitesystems,andnetworkproviders–Useofserialconnectionsofvarioustypestoaccessbandwidthoverlargegeographicareas•ThemajortypesofdevicesthatareusedforWANaccessenvironmentsincluderouters,modems(CSUs/DSUs),andothernetworkingdevicessuchasWANswitches.•WANphysicallayerprotocolsestablishthecodesandelectricalparametersthatthedevicesusetocommunicatewitheachother.Choosingaprotocolislargelydeterminedbythemethodoffacilitationoftheserviceprovider.5-11Ender。ISISSummary(Cont.)•WANsrequiredata-linklayerprotocolstoestablishthelinkacrossthecommunicationlinefromthesendingtothereceivingdevice.•WANconnectionscanbeeitheroveraprivateinfrastructureoroverapublicinfrastructure,suchastheInternet.PrivateWANconnectionsincludebothdedicatedandswitchedcommunicationlinkoptions.5-12Ender。ISIS5-13Ender。ISISConfiguringSerialEncapsulationWide-AreaNetworks5-14Ender。ISISSerialCommunicationLinksSeriallinksuseleasedlinestoprovideadedicatedconnection.5-15Ender。ISISSerialCommunicationLinks(Cont.)•TypicalWANspeedsfortheU.S.:––––T1=(1.544Mb/s)T2=4T1lines(6Mb/s)T3=28T1lines(45Mb/s)T4=168T1lines(275Mb/s)•TypicalWANspeedsforEurope:E1=(2Mb/s)E2=128E0lines(8Mb/s)E3=16E1lines(34M...
