计算机网络与因特网课件.ppt

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1、ComputerNetworksandInternets《计算机网络与因特网》课件厦门大学软件林坤辉PARTIIPacketTransmissionChapter9HardwareAddressingandFrameTypeIdentification硬件编址与帧类型标识9.1IntroductionPhysically,anysignalsentacrossasharednetworkreachesallattachedstations.Atagivenstation,thenetworkin

2、terfacehardwaredetectstheelectricalsignalandextractsacopyoftheframe.Communicationdoesnotusuallyinvolveallstations.Instead,mostcommunicationoccursbecauseanapplicationprogramononecomputersendsdatadirectlytoanapplicationprogramonanother.9.2SpecifyingARe

3、cipient指定接收方MostLANtechnologiesuseanaddressingschemetoprovidedirectcommunication.EachstationontheLANisassignedauniquenumericvaluecalledaphysicaladdress(物理地址),hardwareaddress(硬件地址),ormediaaccessaddress(MAC).AframesentacrossaLANcontainstheaddressofthes

4、endingcomputer,calledasourceaddress,andtheaddressoftheintendedrecipient,calledthedestinationaddress.9.3HowLANHardwareUsesAddressesToFilterPackets局域网硬件如何使用地址过滤包TheLANhardwareinacomputerascompletelyseparatefromthecomputer’sCPUandmemory.TheLANinterfaceh

5、ardwarehandlesallthedetailsofsendingandreceivingframeonthesharedmediumwithoutusingthecomputer’sCPU.TheLANinterfacehardwareusesphysicaladdressingtopreventthecomputerfromreceivingallpacketsthattravelacrosstheLAN.Onceithascapturedacompleteframe,theinter

6、facehardwarecomparesthedestinationaddressintheframetothestation’sphysicaladdress.网卡的任务：检测帧是否存在有效性检验判断是否接收CPU的任务判断是否传给上层处理分层处理的目的：减少CPU的负荷数据包过滤是通信接收方的动作通过检测数据的标识，对符合接收条件的：复制帧中断CPU，将复制后的帧交给CPU继续等待下一个帧对不符合接收条件的：放弃接收，继续等待下一个帧9.4FormatofAPhysicalAddressPh

7、ysicalAddress必须是所在局域网内的唯一标识局域网内要对物理地址提供检索的功能Threebroadcategories:Staticaddress（静态地址）出厂前由生产厂家一次性配置完成全球唯一硬件标识，不会出现地址冲突一次生成，永久使用地址较长，查询慢Configurableaddress（可配置地址）系统出厂后，用户动态分配，保持局域网内唯一地址短，查询快地址可以永久有效，也可以随需求改变Dynamicaddress（动态地址）每当系统启动的时候动态分配，局域网内唯一地址短，查询

8、快有可能出现地址冲突地址动态改变，不利于地址映射表的维护9.5Broadcasting广播Broadcastingwasoriginallyappliedtoradioandtelevisiontransmission.Thenetworkdesignersdefineaspecial,reservedaddressknownasabroadcastaddress(广播地址).Thehardwareinterfaceonacomputerisbuilttorecognizethespecialb