第一章課后習(xí)題及答案

1、第一章1.(Q1)WhatisthedifferencebetweenahostanendsystemListthetypesofendsystems.IsaWebserveranendsystemAnswer:Thereisnodifference.Throughoutthistextthewds“host”“endsystem”areusedinterchangeably.EndsystemsincludePCswkstations

2、WebserversmailserversInterconnectedPDAsWebTVsetc.2.(Q2)Thewdprotocolisoftenusedtodescribediplomaticrelations.Giveanexampleofadiplomaticprotocol.Answer:SupposeAliceanambassadofcountryAwantstoinviteBobanambassadofcountryBo

3、verfdinner.Alicedoesn’tsimplyjustcallBobonthephonesaycometoourdinnertablenow”.InsteadshecallsBobsuggestsadatetime.Bobmayrespondbysayinghe’snotavailablethatparticulardatebutheisavailableanotherdate.AliceBobcontinuetosend“

4、messages”backfthuntiltheyagreeonadatetime.Bobthenshowsupattheembassyontheagreeddatehopefullynotmethan15minutesbefeaftertheagreedtime.DiplomaticprotocolsalsoallowfeitherAliceBobtopolitelycanceltheengagementiftheyhavereaso

5、nableexcuses.3.(Q3)WhatisaclientprogramWhatisaserverprogramDoesaserverprogramrequestreceiveservicesfromaclientprogramAnswer:Awkingprogramusuallyhastwoprogramseachrunningonadifferenthostcommunicatingwitheachother.Theprogr

6、amthatinitiatesthecommunicationistheclient.Typicallytheclientprogramrequestsreceivesservicesfromtheserverprogram.4.(Q4)Listsixaccesstechnologies.Classifyeachoneasresidentialaccesscompanyaccessmobileaccess.Answer:1.Dialup

7、modemovertelephoneline:residential2.DSLovertelephoneline:residentialsmalloffice3.CabletoHFC:residential4.100MbpsswitchedEtherent:company5.WirelessLAN:mobile6.Cellularmobileaccess(fexample3G4G):mobile5.(Q5)Listtheavailabl

8、eresidentialaccesstechnologiesinyourcity.Feachtypeofaccessprovidetheadvertiseddownstreamrateupstreamratemonthlyprice.Answer:Currentpossibilitiesinclude:dialup(upto56kbps)DSL(upto1Mbpsupstreamupto8Mbpsdownstream)cablemode

9、m(upto30Mbpsdownstream2Mbpsupstream.6.(Q7)WhataresomeofthephysicalmediathatEthercanrunoverAnswer:Ethermostcommonlyrunsovertwistedpaircopperwire“thin”coaxialcable.Italsocanrunoverfibersopticlinksthickcoaxialcable.transmit

10、tingsimultaneously)is0.008.10.(Q16)Considersendingapacketfromasourcehosttoadestinationhostoverafixedroute.Listthedelaycomponentsintheendtoenddelay.WhichofthesedelaysareconstantwhicharevariableAnswer:Thedelaycomponentsare

11、processingdelaystransmissiondelayspropagationdelaysqueuingdelays.Allofthesedelaysarefixedexceptfthequeuingdelayswhicharevariable.11.(Q19)SupposeHostAwantstosendalargefiletoHostB.ThepathfromHostAtoHostBhasthreelinksofrate

12、sR1=250kbpsR2=500kbpsR3=1Mbps.a.Assumingnoothertrafficinthewkwhatisthethroughputfthefiletransfer.b.Supposethefileis2millionbytes.RoughlyhowlongwillittaketotransferthefiletoHostBc.Repeat(a)(b)butnowwithR2reducedto200kbps.

13、Answer:a.250kbpsb.64secondsc.200kbps80seconds12.(P2)ConsiderthecircuitswitchedwkinFigure1.8.Recallthattherearencircuitsoneachlink.a.Whatisthemaximumnumberofsimultaneousconnectionsthatcanbeinprogressatanyonetimeinthiswkb.

14、Supposethatallconnectionsarebetweentheswitchintheupperlefthcnertheswitchinthelowerrighthcner.WhatisthemaximumnumberofsimultaneousconnectionsthatcanbeinprogressAnswer:a.Wecannconnectionsbetweeneachofthefourpairsofadjacent

15、switches.Thisgivesamaximumof4nconnections.b.Wecannconnectionspassingthroughtheswitchintheupperrighthcneranothernconnectionspassingthroughtheswitchinthelowerlefthcnergivingatotalof2nconnections.13.(P4)Reviewthecarcaravana