计算机网络专业英语 课件 L9-1 Text 1 Physical Layer and Data Link Layer Devices.pptx
L9-1
Lesson9NetworkDevices;要点KeyPoints
Modulate、encode、hard-code、载波信号
头部、尾部、网段、扭曲、衰减、损耗、拥塞、流控、缓冲、溢出、存储转发、碎片
Stop/resume、income/outgo，Architecture/structure、eliminate、reduce
Ability/capacity,capability
-free结构
First、second、……、finally
;Inadditiontothemedium,networksmayusedevicessuchasmodem,NIC(networkinterfacecard),repeater,bridge,hub,switch,router,andgateway.
Amodem(modulator-demodulator)isanetworkhardwaredevicethatmodulatesoneormorecarrierwavesignalstoencodedigitalinformationfortransmissionanddemodulatessignalstodecodethetransmittedinformation.
Anetworkinterfacecard(NIC),alsoknownasNetworkInterfaceUnit(NIU),ischipsetsonprintedcircuitboardsthatprovidephysicalaccessfromthenodetotheLANmedium.TheNICisresponsibleforfragmentingthedatatransmissionandformattingthedatapacketswiththenecessaryheaderandtrailer.AstandardIEEENICcontainsaunique,hard-codedlogicaladdress(MACaddress),whichisincludedintheheaderofeachdatapacketittransmits.NICsfunctionatthePhysicalandDataLinklayers.;Arepeaterisanetworkdeviceusedtoregenerateasignal.ItoperateswithinthephysicallayeroftheOSIreferencemodelandregeneratesanalogordigitalsignalsthataredistortedbytransmissionlossduetoattenuation.Arepeaterdoesnotmakeintelligentdecisionconcerningforwardingpackets.
Hubscanbeeitheractiveorpassive.Passivehubsactsimplyascable-connectingdevices,whileactivehubsalsoserveassignalrepeatersandarecalled“multi-portrepeaters”.HubsoperateatthePhysicalLayer,withahint示意ofthePhysicalLayeroftheOSIReferenceModel.
BridgesarerelativelysimpledevicesthatconnectLANsofthesamearchitecture架构.BridgesoperateatthelowertwolayersoftheOSIReferenceModel,providingPhysicalLayerandDataLinkLayerconnectivity.BridgesactasLANrepeaterswherespecifieddistancelimitationsareexceeded.Bridgesh