计算机网络复习重点(重点终结版).doc

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1、物理拓扑结构（physicaltopology）网状拓扑结构（meshtopology）各台设备之间都有一条专用的点到点的链路，每台设备必须有n-1个I/O端口星型拓扑结构（startopology）每台设备拥有一条仅与中央控制器连接的点到点专用链路总线拓扑结构（bustopology）环状拓扑结构（ringtopology）协议和标准:w协议是用来管理数据通信的一组规则。协议规定了通信的内容、通信的方式和通信的时间。w标准是由标准化组织协商达成一致的规则。因特网模型（Internetmodel）物理层;数据链路层;网络层;传输层;应用层AnexchangeusingtheIn

2、ternetmodelPhysicallayerNote:Thephysicallayerisresponsiblefortransmittingindividualbitsfromonenodetothenext.DatalinklayerNote:Thedatalinklayerisresponsiblefortransmittingframesfromonenodetothenext.NetworklayerNote:Thenetworklayerisresponsibleforthedeliveryofpacketsfromtheoriginalsourcetothef

3、inaldestination.TransportlayerNote:Thetransportlayerisresponsiblefordeliveryofamessagefromoneprocesstoanother.ApplicationlayerNote:Theapplicationlayerisresponsibleforprovidingservicestotheuser.Summaryofduties===========================================================Positionofthephysicallaye

4、rNote:Frequencyandperiodareinversesofeachother.Note:lAdigitalsignalisacompositesignalwithaninfinitebandwidth.lThebitrateandthebandwidthareproportionaltoeachother.lTheanalogbandwidthofamediumisexpressedinhertz;thedigitalbandwidth,inbitspersecond.lDigitaltransmissionneedsalow-passchannel.lAnal

5、ogtransmissioncanuseaband-passchannel.noiselesschannelnoisychannelAttenuationDistortionNoise===========================================================Unipolar:Unipolarencodingusesonlyonevoltagelevel.Polar:Polarencodingusestwovoltagelevels(positiveandnegative).NRZ-L:InNRZ-Lthelevelofthesigna

6、lisdependentuponthestateofthebit.NRZ-I:InNRZ-Ithesignalisinvertedifa1isencountered.RZencodingAgoodencodeddigitalsignalmustcontainaprovisionforsynchronization.ManchesterencodingInManchesterencoding,thetransitionatthemiddleofthebitisusedforbothsynchronizationandbitrepresentation.DifferentialMa

7、nchesterencodingIndifferentialManchesterencoding,thetransitionatthemiddleofthebitisusedonlyforsynchronization.Thebitrepresentationisdefinedbytheinversionornoninversionatthebeginningofthebit.BipolarInbipolarencoding,weusethreelevels:positive,zero,an