计网-第五章作业.doc

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1、Chapter5作业题，请同学们注意题目描述。1.(R1)Whataresomeofthepossibleservicesthatalink-layerprotocolcanoffertothenetworklayer?Whichoftheselink-layerserviceshavecorrespondingservicesinIP?InTCP?答：可能提供的服务：链路接入，成帧，可靠传输，流量控制，差错检测，差错纠正，半双工和全双工；InIP：成帧，差错检测；InTCP:成帧，可靠传输，差错检测，

2、半双工和全双工。2.(R2)IfallthelinksintheInternetweretoprovidereliabledeliveryservice,wouldtheTCPreliabledeliveryserviceberedundant?Whyorwhynot?答：不会多余，因为TCP保证的是传输层的数据传送，而link提供稳定可靠传输保证链路层的传输稳定，二者不完全重叠，所以TCP可靠传输也不会多余。例如，链路层协议不能保证端到端的顺序，就需要TCP协议进行排序；路由器缓存溢出丢包，链路层协议

3、无法解决这个问题，但是TCP可以。3.(R8)HowbigistheMACaddressspace?TheIPv4addressspace?TheIPv6addressspace?答：248个MACaddresses;232个IPv4addresses;2128个IPv6addresses4.(R9)WhyisanARPquerysentwithinabroadcastframe?WhyisanARPresponsesentwithinaframewithaspecificdestinationMACa

4、ddress?答：因为新加入网络的主机是不知道路由器的IP的，自己也没有IP，所以只能广播才能得到IP，特定的主机就会特定响应。因为每个主机的MAC地址都是唯一的，而ARP建立转发表的时候会带上MAC地址。5.(P5)Considerthe4-bitgenerator,G,showninFigure5.8,andsupposethatDhasthevalue11111010.WhatisthevalueofR?G=1001答：D×2RG的余数，∴R=1106.(P11)Considerabroadcas

5、tchannelwithNnodesandatransmissionrateofRbps.Supposethebroadcastchannelusespolling(withanadditionalpollingnode)formultipleaccess.Supposetheamountoftimefromwhenanodecompletestransmissionuntilthesubsequentnodeispermittedtotransmit(thatis,thepollingdelay)is

6、dpoll.Supposethatwithinapollinground,agivennodeisallowedtotransmitatmostQbits.Whatisthemaximumthroughputofthebroadcastchannel?答：情况1：QRQR+N∙dpoll情况2：N∙QRN∙(QR+dpoll)两种极端情况进行比较，明显情况2为最大值；情况1为最小值。1.(P12)ConsiderthreeLANsinterconnectedbytworouters,asshowninF

7、igure5.38.a.Redrawthediagramtoincludeadapters.Figure5.38Threesubnets,interconnectedbyroutersb.AssignIPaddressestoalloftheinterfaces.ForSubnetIuseaddressesoftheform111.111.111.xxx;forSubnet2usesaddressesoftheform122.222.222.xxx;andforSubnet3useaddressesof

8、theform133.333.333.xxx.（注：本题目略有修改，见红色标注）c.AssignMACaddressestoalloftheadapters.d.ConsidersendinganIPdatagramfromHostAtoHostF.SupposealloftheARPtablesareuptodate.Enumerateallthesteps,asdoneforthesingle-routerexampleinSectio