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1、COMPUTERNETWORKSFOURTHEDITIONPROBLEMSOLUTIONSANDREWS.TANENBAUMVrijeUniversiteitAmsterdam,TheNetherlandsPRENTICEHALLPTRUPPERSADDLERIVER,NJ07458©2003PearsonEducation,Inc.PublishingasPrenticeHallPTRUpperSaddleRiver,NewJersey07458Allrightsreserved.Nopartofthisbookmaybereproduced,inanyf
2、ormorbyanymeans,withoutpermissioninwritingfromthepublisher.PrintedintheUnitedStatesofAmerica10987654321ISBN0-13-046002-8PearsonEducationLTD.PearsonEducationAustraliaPTY,LimitedPearsonEducationSingapore,Pte.Ltd.PearsonEducationNorthAsiaLtd.PearsonEducationCanada,Ltd.PearsonEducación
3、deMexico,S.A.deC.V.PearsonEducation—JapanPearsonEducationMalaysia,Pte.Ltd.PROBLEMSOLUTIONS1SOLUTIONSTOCHAPTER1PROBLEMS1.Thedogcancarry21gigabytes,or168gigabits.Aspeedof18km/hourequals0.005km/sec.Thetimetotraveldistancexkmisx/0.005=200xsec,yieldingadatarateof168/200xGbpsor840/xMbps.
4、Forx<5.6km,thedoghasahigherratethanthecommunicationline.2.TheLANmodelcanbegrownincrementally.IftheLANisjustalongcable.itcannotbebroughtdownbyasinglefailure(iftheserversarereplicated)Itisprobablycheaper.Itprovidesmorecomputingpowerandbetterinteractiveinterfaces.3.Atranscontinentalfib
5、erlinkmighthavemanygigabits/secofbandwidth,butthelatencywillalsobehighduetothespeedoflightpropagationoverthousandsofkilometers.Incontrast,a56-kbpsmodemcallingacomputerinthesamebuildinghaslowbandwidthandlowlatency.4.Auniformdeliverytimeisneededforvoice,sotheamountofjitterinthenet-wo
6、rkisimportant.Thiscouldbeexpressedasthestandarddeviationofthedeliverytime.Havingshortdelaybutlargevariabilityisactuallyworsethanasomewhatlongerdelayandlowvariability.5.No.Thespeedofpropagationis200,000km/secor200meters/µsec.In10µsecthesignaltravels2km.Thus,eachswitchaddstheequivale
7、ntof2kmofextracable.Iftheclientandserverareseparatedby5000km,traversingeven50switchesaddsonly100kmtothetotalpath,whichisonly2%.Thus,switchingdelayisnotamajorfactorunderthesecircumstances.6.Therequesthastogoupanddown,andtheresponsehastogoupanddown.Thetotalpathlengthtraversedisthus16
8、0,000km.Thespeedoflightina