计算机网络答案.docx
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计算机网络答案.docx
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计算机网络答案
SolutionofSelectedExercisesfromtheEndofChapter
Exercises
Chapter1-IntroductionAndOverview
1.1Listtenindustriesthatdependoncomputernetworking.
1.2ProvideabriefhistoryoftheInternetdescribingwhenandhowitwasstarted.
1.3ListthelayersintheTCP/IPmodel,andgiveabriefexplanationofeach.
Answer:
TheTCP/IPconsistsof5layers.Thelayersandtheirshortexplanationisasfollows:
•Layer1:
Physical:
ProtocolsinthePhysicallayerspecifydetailsabouttheunderlyingtransmissionmediumandtheassociatedhardware.
•Layer2:
NetworkInterfaceProtocolsintheNetworkInterfacelayerspecifydetailsaboutcommunicationbetweenhigherlayersofprotocolsandtheunderlyingnetwork.
•Layer3:
Internet:
ProtocolsintheInternetlayerformthefundamentalbasisforthe
Internet.Layer3protocolsspecifycommunicationbetweentwocomputersacrosstheInternet
•Layer4:
Transport:
ProtocolsintheTransportlayerprovideforcommunicationfromanapplicationprogramononecomputertoanapplicationprogramonanother.
•Layer5:
Application:
ProtocolsinthetoplayeroftheTCP/IPstackspecifyhowa
pairoapplicationsinteractwhentheycommunicate.
1.4Whatisaprotocolsuite,andwhatistheadvantageofasuite?
Answer:
protocolsaredesignedincomplete,cooperativesetscalledsuitesorfamilies,insteadofcreatingeachprotocolinisolation.Eachprotocolinasuitehandlesoneaspectofcommunication;together,theprotocolsinasuitecoverallaspectsofcommunication.Theentiresuiteisdesignedtoallowtheprotocolstoworktogetherefficiently.
1.5DescribetheTCP/IPlayeringmodel,andexplainhowitwasderived.
1.6ProvidereasonsforInternetgrowthinrecentyears.
1.7Whatisinteroperability,andwhyisitespeciallyimportantintheInternet?
1.8Accordingtothetext,isitpossibletodevelopInternetapplicationswithoutunderstandingthearchitectureoftheInternetandthetechnologies?
Supportyouranswer.
Answer:
Yes,possibletowritecodethatcommunicatesoveranetwork,withoutunderstandingthehardwareandsoftwaretechnologiesthatareusedtotransferdatafromoneapplicationtoanother.However,knowledgeoftheunderlyingnetworksystemallowsaprogrammertowritebettercode.
1.9Towhataspectsofnetworkingdoesdatacommunicationsrefer?
Answer:
Datacommunicationsreferstothestudyoflow-levelmechanismsandtechnologiesusedtosendinformationacrossaphysicalcommunicationmedium,suchasawire,radiowave,orlightbeam.
1.10Whatisacommunicationprotocol?
Conceptually,whattwoaspectsofcommunicationdoesaprotocolspecify?
Answer:
Acommunicationprotocolrefertoaspecificationfornetworkcommunication.Majoraspectsofaprotocolaresyntax(format)andsemantics(meaning)oftheprotocol.
1.11Listmajorstandardizationorganizationsthatcreatestandardsfordatacommunicationsandcomputernetworking.
Answer:
Variousnationalandinternationalorganizationsareinvolvedinstandardizationofcommunicationsandnetworkingservices.Tolistfew:
•InternationalOrganizationforStandardization(ISO)
•InternationalTelecommunicationsUnion,TelecommunicationStandardization
Sector(ITU-T)
•InstituteofElectricalandElectronicsEngineers(IEEE)
•InternetEngineeringTaskForce(IETF)
1.12GiveabriefexplainofthelayersintheISOOpenSystemInterconnectionmodel.
Answer:
ISOOSImodelconsistsof7layers,namely:
•Layer7:
Application
•Layer6:
Presentation
•Layer5:
Session
•Layer4:
Transport
•Layer3:
Network
•Layer2:
DataLink
•Layer1:
Physical
Readerisexpectedtofindoutshortexplanationofeachlayer.
1.13Whatispacket-switching,andwhyispacketswitchingrelevanttotheInternet?
Answer:
Packetswitchingdividesdataintosmallblocks,calledpackets,andincludesanidentificationoftheintendedrecipientineachpacket.Packetswitchingchangednetworkinginafundamentalway,andprovidedthebasisforthemodernInternet.Packetswitchingallowsmultiplesenderstotransmitdataoverasharednetwork.
1.14Explainhowheadersareaddedandremovedasdatapassesthroughalayeredmodel.
Answer:
eachlayeronthesendingcomputerprependsextrainformationontothepacket;thecorrespondingprotocollayeronthereceivingcomputerremovesandusestheextrainformation.
Chapter-2InternetTrends
2.1DescribetheevolutioninaudiothathasoccurredintheInternet.
Answer:
Thetrendinaudioprocessinghasbeenasfollows:
AlertSoundsÆHumanVoiceÆAudiClipsÆHigh-FidelityAudio
2.2AssumethatonehundredmillionnewcomputersareaddedtotheInterneteachyear.Ifcomputersareaddedatauniformrate,howmuchtimeelapsesbetweentwosuccessiveadditions?
2.3DescribeInternetapplicationsthatyouuseregularlythatwerenotavailabletoyourparentswhentheywereyourage.
2.4Whywassharingofcomputationalresourcesimportantinthe1960s?
2.5WhatshiftinInternetuseoccurredwhentheWorldWideWebfirstappeared?
2.6TheplotinFigure2.1showsthatInternetgrowthdidnotstartuntilafter1995.Whyisthefiguremisleading?
Answer:
ResearcherscomputersworkingfortheAdvancedResearchProjectsAgency(ARPA)ofUSDepartmentofDefense(DoD)neededpowerfulandcomputerswereincrediblyexpensive.TheARPAbudgetwasinsufficienttofundmanycomputers.TheARPAplannedtointerconnectallcomputerswithadatanetworkanddevisesoftwarethatwouldallowaresearchertousewhichevercomputerwasbestsuitedtoperformagiventask.
2.7ListthestepsinthetransitioningraphicspresentationfromtheearlyInternettothecurrentInternet.
Answer:
Thetrendinthegraphicpresentationhasbeenasfollows:
TextÆGraphicImagesÆVideoClipsÆFull-MotionVideo
2.8WhatInternettechnologyisthetelephonesystemusing?
Answer:
SomecurrenttelephonesystemsusesVoice-OverIPtechnology.Readerisencouragedtorefertolaterchaptersfordetails.
2.9ExtendtheplotinFigure2.2,andestimatehowmanycomputerswillbeconnectedtotheInternetby2020.
2.10WhatimpactisInternettechnologyhavingonthecabletelevisionindustry?
2.11ListfournewInternetapplications,andtellthegroupsforwhicheachisimportant.
2.12WhyistheswitchfromwiredInternetaccesstowirelessInternetaccesssignificant?
Chapter3-InternetApplicationsAndNetworkProgramming
3.2WhatarethetwobasiccommunicationparadigmsusedintheInternet?
Answer:
Therearevariousapproaches,butaccordingtotextbook,wecanspecifythemasStreamParadigmandMessageParadigm.
3.12GivesixcharacteristicsofInternetstreamcommunication.
Answer:
CharacteristicsofInternetstreamcommunicationcanbelistedasfollows:
•Connection-oriented
•1-to-1communication
•Sequenceofindividualbytes
•Arbitrarylengthtransfer
•Usedformultimediaapplications
•BuiltonUDPprotocol
3.4GivesixcharacteristicsofInternetmessagecommunication.
Answer:
CharacteristicsofInternetmessagecommunicationcanbelistedasfollows:
•Connectionless
•Many-to-manycommunication
•Sequenceofindividualmessages
•Eachmessagelimitedto64Kbytes
•Usedbymostapplications
•BuiltonTCPprotocol
3.13Ifasenderusesthestreamparadigmandalwayssends1024bytesatatime,whatsizeblockscantheInternetdelivertoareceiver?
Answer:
streamparadigmdoesnotprovideanyguaranteesforblocksizes,soalldependsonindividualtransfer.
3.6Ifasenderwantstohavecopiesofeachdatablockbeingsenttothreerecipients,whichparadigmshouldthesenderchoose?
Answer:
Themessageparadigmissuitableforsuchtransfer,sinceitallowsmany-to-manycommunication
3.21WhatarethethreesurprisingaspectsoftheInternet’smessagedeliverysemantics?
Answer:
TheInternet’smessagedeliveryhasthefollowingundesirablecharacteristics:
•Messagescanbelost
•Messagescanbeduplicated
•Messagescanbedeliveredout-of-order
3.19Givethegeneralalgorithmthataconnection-orientedsystemuses.
Answer:
Theinteractionbetweentwoconnection-orientedpartiescanbesummarizedas:
•Setting-upconnectionbetweentwoparties
•Exchangeinformation
•Terminatetheconnection
3.25WhentwoapplicationscommunicateovertheInternet,whichoneistheserver?
Answer:
Theapplicationthatwaitsforsomeotherapplicationstocontactiscalledserver,andtheapplicationthatcontactotheroneiscalledclient.
3.14Compareandcontrastaclientandserverapplicationbysummarizingcharacteristicsofeach.
3.5Whatisthedifferencebetweenaserverandaserver-classcomputer?
Answer:
Theservertermreferstoaprogramthatwaitspassivelyforcommunication,
andnottothecomputeronwhichitexecutes.However,whenacomputerisdedicatedtorunningoneormoreserverprograms,thecomputeritselfissometimescalledaserver.HardwarevendorscontributetotheconfusionbecausetheyclassifycomputersthathavefastCPUs,largememories,andpowerfuloperatingsystemsasservermachines.
3.20Candataflowfromaclienttoaserver?
Explain.
Answer:
Yes,datamayflowinbothdirections(clientÆserverandserverÆclient).
3.15Listthepossiblecombinationsofclientsandserversagivencomputercanrun.
3.7Canallcomputersrunmultipleserviceseffectively?
Whyorwhynot?
3.22Whattwoidentifiersareusedtospecifyaparticularserver?
Answer:
Aparticularserverisidentifiedbythefollowingidentifiers:
•Anidentifierforthecomputeronwhichaserverruns(IPAddress)
•Anidentifierforaparticularserviceonthecomputer(PortNumber)
3.8Listthestepsaclientusestocontactaserverafterauserspecifiesadomainnamefortheserver.
Answer:
Thestepsthataclientusest
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