计算机网络试题

1.ExplainClient-Servermodelfordistributedcomputingbyexample.Client-servermodelcanmakecomputingfasterthanjustusetheservertocomputingandtheclientjustbeabrowser.Forexample,thedatastoredinapowerfulservermachine,andthecilentconnectedwiththeserverbyinternet,itmaniplationdataatlocalcilent,sotheservercanhandlemorerequestfromotherclients,andtheclientcanmakefulluseofithardwareresource.Sothedistributedcomputingcanbeveryfast.2.ExplainPeer-to-PeermodelfordistributedcomputingbyexamplePeer-to-Peermodelmeansindividualswhoformaloosegroupcancommunicatewithothersinthegroup,everyoneinthisgroupcancommunicatewithoneormoreotherpeople,andeveronecanbeclientsandservers.Forexample,ifweuseBitTorrenttodownloadafilm,wedownloaditfromotherpeoplewhoalsohavethissoftwareandtheresource,notjustfromoneortwoserver.Atthesametime,ourresourcesalsobesharedanddownloadedbyotherpeople,itmakesthespeedofthetransmissionmorefasterthanbefore..3.CompareconceptsofBroadcasting,Multicasting,Unicasting.Broadcasting:Broadcastsystemsusuallyallowthepossibilityofaddressingapackettoalldestinationsbyusingaspecialcodeintheaddressfield.Whenapacketwiththiscodeistransmitted,itisreceivedandprocessedbyeverymachineonthenetwork.Multicasting:Ifboradcastsystemsalsosupporttaransmissiontoasubsetofthemachine,itcalledmulticasting.Unicasting:Point-to-pointtransmissionwithexactlyonesenderandexactlyonereceiverissometimescalledunicasting.4.Whatarethetwogenerallyacceptedanglesbywhichcomputernetworkscanbeclassified?ItcanbeclassifiedfromNetworknodedistributionandNetworkTopology.5.DescribesomecharacteristicsoftheEthernet.Ethernetoftenusedinlocalareanetworks,isthemostcommontypeofwiredLAN.itusecopperwires,opticalfibers.anditframeinIEEE802.36.HowisaWANorganized?explainpacket-switchedprinciple.WANspansalargegeographicalarea,oftenacountryorcontinent,andlesslines,InWAN,thehostsandsubnetareownedandoperatedbydifferentpeople.Andbeforethemessagebesended,itwillbecutintopackets,everypackets’sheaderbeinsertedsomemessageaboutthetargetaddress,andthenpostthem,bereceivedateachintermediaterouter.7.Whataretworeasonsforusinglayeredprotocols?①Itcanreducethedesigncomplexity,everylayerjustneedtoconcernaboutit’sownfuction.②iftheprotocolschanges,theotherlayers’protocolsdon’tneedtochange.8.Whatistheprincipaldifferencebetweenconnectionlesscommunicationandconnection-orientedcommunication?Connection-orientedserviceneedtoestablishaconnectionanduntiltheconnectionestablishsuccess,itstartsthedatatransmission.ifthetransmissionstop,itclosetheconnection,andthedatatransmissionisordered.Connectionlessservice:eachmessagecarriesthefulldestinationaddressandeachoneisroutedthroughtheintermediatenodesinsidethesystemindependentofallthesubsequentmessages.andthereceivergetthemessagesunordered.9.Explaintherelationshipbetweenservicesandprotocols.Theservicedefineswhatoperationsthelayerispreparedperformonit’susers,butdoesn’tsayhowtheseoperationsareimplemented.andit’sonalowlevel.Theprotocolisasetofrulesgoverningtheformatandmeaningofthepackets,ormessagesthatareexchangedbythepeerentitieswithinalayer(同一层上的对象)entitiesuseprotocolstoimplement(实施)theirserevicedefinitions.10.WhichoftheOSIlayershandleseachofthefollowing:(a)Dividingthetransmittedbitstreamintoframes.DataLinkLayer(b)Determiningwhichroutethroughthesubnettouse.NetworkLayer11.Iftheunitexchangedatthedatalinkleveliscalledaframeandtheunitexchangedatthenetworkleveliscalledapacket,doframesencapsulatepacketsordopacketsencapsulateframes?Explainyouranswer.Doframesencapsulatepackets,becausethedatalinklevelislowerthannetworklevel,thepacketwhichfromnetworklevelneettobeencapsulatedinframe’sdataheader,andthesenttophysicallayer.12.Asystemhasann-layerprotocolhierarchy(分层协定).ApplicationsgeneratemessagesoflengthMbytes.Ateachofthelayers,anh-byteheaderisadded.Whatfractionofthenetworkbandwidthisfilledwithheaders?h*n/(M+h*n)13.Supposethealgorithmusedtoimplementtheoperationsatlayerkischanged,howdoesthisimpactoperationsatlayersk-1andk+1?Itdoesn’tinfluencethelayerk+1andk-1;14.Supposethereisachangeintheservice(setofoperations)providedbylayerk,howdoesthisimpactservicesatlayersk-1andk+1?Itdoesn’tinfluencethelayerk+1andk-1;15.ListtwowaysinwhichtheOSIreferencemodelandtheTCP/IPreferencemodelarethesame.Nowlisttwowaysinwhichtheydiffer.Same①theyallneedlayerforeachdifferentlevelofabstarction②eachlayerperformsafunction.Difference:①OSIreferencemodelhavesevenlevel,andtcp/ipjusthasfourlevel.②OSIsupportsbothinthenetworklayer,tcp/ipsupportsonlyconnectionlessmodeinthenetworklayer.16.PleasedrawadiagramshowingtheOSIreferencemodel.sorry…17.WhatisthemaindifferencebetweenTCPandUDP.Tcpisconnection-orientedprotocol.UDPisconnectionlessprotocol.Tcp’stransmittedmessageisordered,andUDP’snot18.Whenafileistransferredbetweentwocomputers,twoacknowledgementstrategiesarepossible.Inthefirstone,thefileischoppedupintopackets,whichareindividuallyacknowledgedbythereceiver,butthefiletransferasawholeisnotacknowledged.Inthesecondone,thepacketsarenotacknowledgedindividually,buttheentirefileisacknowledgedwhenitarrives.Discussthesetwoapproaches.Firstone:i