计网_第三章作业.doc

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1、.专业.专注.Chapter3注：括弧中标题号为第四版教材中对应的习题号1.(R14)SupposeHostAsendstwoTCPsegmentsbacktobacktoHostBoveraTCPconnection.Thefirstsegmenthassequencenumber90;thesecondhassequencenumber110.a.Howmuchdataisinthefirstsegment?b.SupposethatthefirstsegmentislostbutthesecondsegmentarrivesatB.IntheacknowledgmentthatHos

2、tBsendstoHostA,whatwillbetheacknowledgmentnumber?答：a．[90,109]=20bytesb．acknumber=90，对第一个报文段确认2.(R15)Trueorfalse?a.ThesizeoftheTCPRcvWindowneverchangesthroughoutthedurationoftheconnection.b.supposeHostAissendingHostBalargefileoveraTCPconnection.ThenumberofunacknowledgedbytesthatAsendscannotexceedth

3、esizeofthereceivebuffer.c.HostAissendingHostBalargefileoveraTCPconnection.AssumeHostBhasnodatatosendHostA.HostBwillnotsendacknowledgmentstoHostA.word完美格式..专业.专注.becauseHostBcannotpiggybacktheacknowledgmentondata.d.TheTCPsegmenthasafieldinitsheaderforRcvWindow.e.SupposeHostAissendingalargefiletoHos

4、tBoveraTCPconnection.Ifthesequencenumberforasegmentofthisconnectionism,thenthesequencenumberforthesubsequentsegmentwillnecessarilybem+1.f.SupposethatthelastSampleRTTinaTCPconnectionisequalto1sec.ThecurrentvalueofTimeoutIntervalfortheconnectionwillnecessarilybe>=1sec.g.SupposeHostAsendsonesegmentwi

5、thsequencenumber38and4bytesofdataoveraTCPconnectiontoHostB.Inthissamesegmenttheacknowledgmentnumberisnecessarily42.答：a.Fb.Tc.F：即使没有数据传送，也会进行单独确认d.Te.F：按字节编号，不按报文段编号f.Fg.F：B->A的确认号不一定为38+4=421.(R17)Trueorfalse?ConsidercongestioncontrolinTCP.Whenthetimerexpiresatthesender,thethresholdissettoonehalfo

6、fitspreviousvalue.答：.word完美格式..专业.专注.F：应为当前拥塞窗口的一半，而不是阈值的一半。1.(P3)UDPandTCPuse1scomplementfortheirchecksums.Supposeyouhavethefollowingthree8-bitbytes:01101010,01001111,01110011.Whatisthe1scomplementofthesumofthese8-bitbyte?(NotethatalthoughUDPandTCPuse16-bitwordsincomputingthechecksum,forthisprobl

7、emyouarebeingaskedtoconsider8-bitsums.)Showallwork..WhyisitthatUDPtakescomplementofthesum;thatis,whynotjustusethesum?Withthe1scomplementscheme,howdoesthereceiverdetecterrors?Isitpossiblethata1-biterrorwillgoundet