大三上課程-計(jì)算機(jī)網(wǎng)絡(luò)chapter

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教授課程老1AsiaPacific-RedAsia/Africa-GreenNorthAmerica-LatinAmericanandCaribbean-RFC1918AddressesCyanUnknown-23ComputerNetworksComputerNetworks.4weekExam(tobe5計(jì)算機(jī)網(wǎng)絡(luò)自頂向下方法(第4版ComputerNetworking:ATopDownApproach,4thedition.JimKurose,KeithRossAddison-Wesley,Aug.2009.6計(jì)算機(jī)網(wǎng)絡(luò)技 —自頂向下分析與設(shè)?機(jī)械工2010年37）計(jì)算機(jī)網(wǎng)絡(luò)（第五）謝電子工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、環(huán)形Ring、總線形Bus、樹(shù)形Tree星形拓

環(huán)形拓

（c）總線形拓 (d)樹(shù)形拓 (e)網(wǎng)狀拓STARtopology-connectsallcablestoacentralpointofconcentration.Thispointisusuallyahuborswitch.Ithasafocalpointwherealltheresourcesarethere.RINGtopology–connectsonehosttothenextandthelasthosttothefirst.Thiscreatesaphysicalringofcable. BUStopology–usesasinglebackbonesegment(lengthofcable)thatallthehostsconnecttodirectly.Theideaisthatisjustlikeridingabus.Ithasonlyonedriverandmanypassengerswhoareriding當(dāng)一個(gè)結(jié)點(diǎn)利用總線收數(shù)如果有兩個(gè)及以上的結(jié)點(diǎn)同時(shí)利用公共總線發(fā)送據(jù)時(shí)，就會(huì)出，造成傳輸失敗優(yōu)點(diǎn)：結(jié)構(gòu)簡(jiǎn)單 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(分組)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資源子網(wǎng)resourcesubnet直接面向用由主機(jī)系統(tǒng)、終端、各種網(wǎng)絡(luò)軟件與數(shù)據(jù)資源通信子網(wǎng)communicationsubnet負(fù)責(zé)通由路由器、通信線路組networkedge網(wǎng)絡(luò)邊緣applicationsandaccessnetworks接入網(wǎng)wired,wirelesscommunicationlinksneokcore網(wǎng)絡(luò)核interconnected互聯(lián)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住宅接網(wǎng)institutionalaccess(school,機(jī)關(guān)接入網(wǎng)(學(xué)校，公司mobileaccess移動(dòng)接入Keepinbandwidth帶寬(bitspersecond)ofaccesssharedordedicated?共享Dialupviamodem經(jīng)調(diào)制解調(diào)器撥upto56KbpsdirectaccessCan’tsurfandphoneatsametime:can’tbe“alwayson”DSLdigitalsubscriberlinedeployment部署 ephonecompanyupto1Mbpsupstream上行(todaytypically<kbps)upto8Mbpsdownstream下行(todaytypically<1Mbps)dedicated( 的)physicalline ephone HFC:hybridfibercoax光纖同軸混Asymmetric不對(duì)稱(chēng)upto30Mbpsdownstream,2MbpsnetworkofcableandfiberattacheshomestoISProuterhomesshareaccesstodeployment:availablecableTVcompaniescompany/univlocalareanetwork(LAN)connectsendsystemtoedgerouter邊界路由LANsEthernet以太網(wǎng)10Mbs,100Mbps,1Gbps,10Gbpsmodernconfiguration:endsystemsconnectintoEthernetsharedwirelessaccessnetworkconnectsendsystemtorouter通過(guò)viabaseaka“accesspoint”接入wireless802.11b/g(WiFi):11or Mbpswider-areawirelessaccessprovided operator由電公司運(yùn)營(yíng)商提~1Mbpsovercellularsystem蜂窩(兩種標(biāo)準(zhǔn)：EVDO,HSDPA)WiMAX(10’sMbps)overwide

Typicalhomenetworkcomponents:DSLorcablemodem wirelessaccess

meshofinterconnectedfundamentalquestion:howdatatransferredthroughcircuitswitching電路交換:dedicatedcircuitpercall每 e.g., ephonepacket-switching分組交換:datasentthrunetindiscrete“chunks”離散的塊e.g.,Internet接入設(shè)

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