大三上课程-计算机网络chapter

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教授课程老1AsiaPacific-RedAsia/Africa-GreenNorthAmerica-LatinAmericanandCaribbean-RFC1918AddressesCyanUnknown-23ComputerNetworksComputerNetworks.4weekExam(tobe5计算机网络自顶向下方法(第4版ComputerNetworking:ATopDownApproach,4thedition.JimKurose,KeithRossAddison-Wesley,Aug.2009.6计算机网络技 —自顶向下分析与设•机械工2010年37）计算机网络（第五）谢电子工2008年18Aboutmyself…Contact:lip 9Thischapterswillcoverthefollowingareas,ComputernetworkAcollectionofcomputingdevicesthatareconnectedinvariouswaysinordertocommunicateandshareresourcesUsually,theconnectionsbetweencomputersinanetworkaremadeusingphysicalwiresorcablesHowever,someconnectionsarewireless,usingradiowavesorinfraredsignalsThegenerictermnodeorhostreferstoanydeviceonanetworkDatatransferrateThespeedwithwhichdataismovedfromoneplaceonanetworktoanotherDatatransferrateisakeyissueincomputernetworks-Computernetworkshaveopenedupanentirefrontierintheworldofcomputingcalledtheclient/servermodel -FileserverAcomputerthatstoresandmanagesfilesformultipleusersonaWebserverAcomputerdedicatedtorespondingtorequests(fromthebrowserclient)forwebpages-LocalAreaMetropolitanAreaWideAreaClassificationofinterconnectedprocessorsbyscale.Alocalareanetwork(LAN)isacomputernetworkthatinterconnectscomputersinalimitedareasuchasahome,school,computerlaboratory,orofficebuildingusingnetworkmedia.TOPOLOGY–definesthestructureofthenetwork.Therearetwopartstothetopologydefinition:thephysicaltopologywhichistheactuallayoutofthewire(media)andthelogicaltopologywhichdefineshowthemediaisaccessedbythehosts.Itrefersalsotohowcomputersarebeingconnectedwitheachother.Variousconfigurations,calledtopologies,havebeenusedtoadministerLANsRingtopologyAconfigurationthatconnectsallnodesinaclosedlooponwhichmessagestravelinonedirectionStartopologyAconfigurationthatcentersaroundonenodetowhichallothersareconnectedandthroughwhichallmessagesaresentBustopologyAllnodesareconnectedtoasinglecommunicationlinethatcarriesmessagesinboth-VariousnetworkAbustechnologycalledEthernethas etheindustrystandardforlocal-areanetworks

15- 星形Star、环形Ring、总线形Bus、树形Tree星形拓

环形拓

（c）总线形拓 (d)树形拓 (e)网状拓STARtopology-connectsallcablestoacentralpointofconcentration.Thispointisusuallyahuborswitch.Ithasafocalpointwherealltheresourcesarethere.RINGtopology–connectsonehosttothenextandthelasthosttothefirst.Thiscreatesaphysicalringofcable. BUStopology–usesasinglebackbonesegment(lengthofcable)thatallthehostsconnecttodirectly.Theideaisthatisjustlikeridingabus.Ithasonlyonedriverandmanypassengerswhoareriding当一个结点利用总线收数如果有两个及以上的结点同时利用公共总线发送据时，就会出，造成传输失败优点：结构简单 communicationinfrastructuresthathavebeendevelopedinandaroundlargecities-TheIEEE802-2002standarddescribesaMANasbeing:“AMANisoptimizedforalargergeographicalareathanaLAN,rangingfromseveralblocksofbuildingstoentirecities.MANscanalsodependoncommunicationschannelsofmoderate-to-highdatarates.AMANmightbeownedandoperatedbyasingleorganization,butitusuallywillbeusedbymanyindividualsandorganizations.MANsmightalsobeownedandoperatedaspublicutilities.Theywilloftenprovidemeansforinternetworkingoflocalnetworks.”Wide-areanetwork(WAN) Anetworkthatconnectstwoormorelocal-areanetworksoverapotentiallylargegeographicdistanceOftenoneparticularnodeonaLANissetuptoserveasagatewaytohandleallcommunicationgoingbetweenthatLANandothernetworksCommunicationbetweennetworksiscalledTheInternet,asweknowittoday,isessentiallyultimatewide-areanetwork,spanningtheentireglobe-wideareanetwork(WAN)isanetworkthatcoversabroadarea(i.e.,any municationsnetworkthatlinksacrossmetropolitan,regional,ornationalboundaries)usingprivateorpublicnetworktransports.Businessand ernmententitiesutilizeWANstorelaydataamongemployees,clients,buyers,and fromvariousgeographicallocations.Inessence,thismodeof municationallowsabusinesstoeffectivelycarryoutitsdailyfunctionregardlessoflocation.TheInternetcanbeconsideredaWANaswell,andisusedbybusinesses,ernments,organizations,andindividualsforalmostanypurposeimaginable.SeveraloptionsareavailableforWANconnectivity:HostnameAuniqueidentificationthatspecifiesaparticularcomputerontheForexamplecon-NetworksoftwaretranslatesahostnameintoitscorrespondingIPaddressForexample-AnIPaddresscanbesplitnetworkaddress,whichspecifiesaspecifichostnumber,whichspecifiesaparticularmachineinthatnetworkAnIPaddressisstoredinfour-Ahostnameconsistsofthecomputernamefollowedbythe is name nameisseparatedintotwoormoresectionsthatspecifytheorganization,andpossiblyasubsetofanorganization,ofwhichthecomputerisaTwoorganizationscanhaveacomputernamedthesamethingbecausethe namemakesitclearwhichoneisbeingreferredto-Theverylastsection he iscalled s,includingsomerelativelynew OrganizationsbasedincountriesotherthantheUnitedStatesuseatop-level correspondstotheirtwo-lettercountrycodesSomeofthetop-namesbasedoncountry-The namesystem(DNS)ischieflyusedtotranslatehostnamesintonumericIPaddressesDNSisanexampleofadistributeddatabaseIfthatservercanresolvethehostname,itdoesIfnot,thatserverasksanother server-Well,nobodydoes.Nosingle companyownstheInternetorevencontrolsitentirely.Asawide-areanetwork,itismadeupofmanysmallernetworks.Thesesmallernetworksareoftenownedandmanagedbya rganization.TheInternet,then,isreallydefinedbyhowconnectionscanbemadebetweenthesenetworks.-area -InternetbackboneAsetofhigh-speednetworksthatcarryInternettrafficThesenetworksareprovidedbycompaniessuchasAT&T,GTE,andIBMcompanythatprovidesothercompaniesorindividualswithaccesstothe-TherearevarioustechnologiesavailablethatyoucanusetoconnectahomecomputertotheInternetAphonemodemconvertscomputerdataintoan audiosignalfortransferovera ephoneline,andthenamodematthedestinationconvertsitbackagainintoAdigitalsubscriberline(DSL)usesregularcopperphonelinestotransferdigitaldatatoandfromthephonecompany’scentralofficeAcablemodemusesthesamelinethatyourcablesignalscomeinontotransferthedatabackand-BroadbandAconnectioninwhichtransferspeedsarefasterthan128bitspersecondDSLconnectionsandcablemodemsarebroadbandconnectionsThespeedfordownloads(gettingdatafromtheInternettoyourhomecomputer)maynotbethesameasuploads(sendingdatafromyourhomecomputertotheInternet)-Toimprovetheefficiencyoftransferringinformationoverasharedcommunicationline,messagesaredividedintofixed-sized,numberedpackets(分组)Networkdevicescalledroutersareusedtopacketsbetweensentby15- NetworkprotocolsarelayeredsuchthateachonereliesontheprotocolsthatunderlieitSometimesreferredtoasaprotocolFigure15.6Layeringofkeynetwork-TCPstandsforTransmissionControlTCPsoftwarebreaksmessagesintopackets,handsthemofftotheIPsoftwarefordelivery,andthenordersandreassemblesthepacketsattheirdestinationIPstandsforInternetIPsoftwaredealswiththeroutingofpacketsthroughthemazeofinterconnectednetworkstotheirfinaldestination-UDPstandsforUserDatagramItisanalternativetoTCPThemaindifferenceisthatTCPishighlyreliable,atthecostofdecreasedperformance,whileUDPislessreliable,butgenerallyfaster-OtherprotocolsbuildonthefoundationestablishedbytheTCP/IPprotocolsuiteSimpleMailTransferProtocolFileTransferProtocolHyperTextTransferProtocol-andtheportstheyuse-Relatedtotheideaofnetworkprotocolsandstandardizationistheconceptofafile’sMIMEtypeMIMEstandsforMultipurposeInternetMailBasedona ’sMIMEtype,anapplicationprogramcandecidehowtodealwiththedataitisgiven-FirewallAmachineanditssoftwarethatserveasaspecialgatewaytoanetwork,protectingitfrominappropriateaccessFiltersthenetworktrafficthatcomescheckingthevalidityofthemessagesasmuchaspossibleandperhapsdenyingsomemessagesaltogetherEnforcesanorganization’saccesscontrol-Afirewallprotectinga humanGotGot

computernetworkTCPTCPconnectionGet /kurose-msgssentandreceivedamongnetworkentities,andactions资源子网resourcesubnet直接面向用由主机系统、终端、各种网络软件与数据资源通信子网communicationsubnet负责通由路由器、通信线路组networkedge网络边缘applicationsandaccessnetworks接入网wired,wirelesscommunicationlinksneokcore网络核interconnected互联的路由 endsystems(hosts)端系runapplicationprograms,e.g.Web,

peer-lt“tekelclienthostrequests,servicefromalways-on

peer-peermodel:minimal(orno)useofdedicatedserverse.g.Skype,Q:Howtoconnectendsystemsedgeresidentialaccessnets住宅接网institutionalaccess(school,机关接入网(学校，公司mobileaccess移动接入Keepinbandwidth带宽(bitspersecond)ofaccesssharedordedicated?共享Dialupviamodem经调制解调器拨upto56KbpsdirectaccessCan’tsurfandphoneatsametime:can’tbe“alwayson”DSLdigitalsubscriberlinedeployment部署 ephonecompanyupto1Mbpsupstream上行(todaytypically<kbps)upto8Mbpsdownstream下行(todaytypically<1Mbps)dedicated( 的)physicalline ephone HFC:hybridfibercoax光纤同轴混Asymmetric不对称upto30Mbpsdownstream,2MbpsnetworkofcableandfiberattacheshomestoISProuterhomesshareaccesstodeployment:availablecableTVcompaniescompany/univlocalareanetwork(LAN)connectsendsystemtoedgerouter边界路由LANsEthernet以太网10Mbs,100Mbps,1Gbps,10Gbpsmodernconfiguration:endsystemsconnectintoEthernetsharedwirelessaccessnetworkconnectsendsystemtorouter通过viabaseaka“accesspoint”接入wireless802.11b/g(WiFi):11or Mbpswider-areawirelessaccessprovided operator由电公司运营商提~1Mbpsovercellularsystem蜂窝(两种标准：EVDO,HSDPA)WiMAX(10’sMbps)overwide

Typicalhomenetworkcomponents:DSLorcablemodem wirelessaccess

meshofinterconnectedfundamentalquestion:howdatatransferredthroughcircuitswitching电路交换:dedicatedcircuitpercall每 e.g., ephonepacket-switching分组交换:datasentthrunetindiscrete“chunks”离散的块e.g.,Internet接入设

TypesoftransmissiontechnologyBroadcastPoint-to-pointOnlyOnlyDdatafrom NotNotNotNotNotNot

TimBerners-LeewasthemanleadingthedevelopmentoftheWorldWideWeb(withhelpofcourse),thedefiningofHTML(hypertextmarkuplanguage)usedtocreatewebpages,HTTP(HyperTextTransferProtocol)andURLs(UniversalResourceLocators).Allofthosedevelopmentstookplacebetween1989and#of0Dec-70Dec-71Dec-72Dec-73Dec-74Dec-75Dec-76Dec-77Dec-78Dec-79