計算機網(wǎng)絡(luò)1課件

ComputerNetworks參考文獻AndrewS.Tanenbaum,ComputerNetworks(FourthEdition),清華大學(xué)出版社&PrenticeHall,2004JamesF.Kurose等著，陳鳴譯.計算機網(wǎng)絡(luò)—自頂向下方法與Internet特色（第三版）.機械工業(yè)出版社，2005

謝希仁.計算機網(wǎng)絡(luò)（第四版）.電子工業(yè)出版社，2003

ContentsIntroduction(7)1ThePhysicalLayer(5)2TheDataLinkLayer(6)3TheMACSub-layer(6)4TheNetworkLayer(6)5TheTransportLayer(4)6TheApplicationLayer(4)7NetworkSecurity(4)8Whatiscomputernetworks?ComputerNetwork:meansacollectionofautonomouscomputers（自主/自治計算機）interconnected.Itiscomposedofhosts,protocolsandcommunication-subnet.

ThedifferencebetweenComputerNetworkandDistributedSystem

DistributedSystem:Acollectionofautonomous(independent)computersistransparency（透明的）toitsusers.Itisasoftwaresystembuiltontopofanetwork.Thus,thekeydistinctionbetweenanetworkandadistributedsystemisthesoftware(especiallytheoperatingsystem:NOSandDistributedOS),ratherthanthehardware.

Thedevelopmentofcomputernetworks

First,Terminal-orientednetwork

（1）Computingtechnologyandcommunicationtechnology.（2）Circuit-exchange(電路交換):Connectionestablishment,Datatransform,Connectionrelease.

Second,Packet-exchangenetwork:1969.11,ARPANET

Thedevelopmentofcomputernetworks

(a)Circuitswitching(b)Messageswitching(c)Packetswitching1.1UsesofComputerNetworksBusinessApplicationsHomeApplications

MobileUsersSocialIssues

BusinessApplicationsThegoalsofthecomputernetworks:Resourcesharing

（hardware、softwareandData，資源共享）

Communicationmedium（通信手段）HomeApplicationsAccesstoremoteinformation(訪問遠(yuǎn)程信息)Persontopersoncommunication(個人間通信)Interactiveentertainment(交互式娛樂)E－commerce(電子商務(wù))Broadlyspeaking(從廣義上講)，twotypesoftransmissiontechnology:（1）Broadcastlinks（2）Point-to-pointlinksBroadcastnetwork(廣播式網(wǎng)絡(luò))：broadcastingandmulticastingPoint-to-pointnetwork(點到點網(wǎng)絡(luò))：packet－transmission(分組轉(zhuǎn)發(fā))androuting－algorithms（路由選擇）LocalAreaNetworks(局域網(wǎng))Threecharacteristics:(1)Size(范圍)(2)Transmissiontechnology(傳輸技術(shù))(3)Topology(拓?fù)浣Y(jié)構(gòu))WideAreaNetworks(廣域網(wǎng))WirelessNetworksCategoriesofwirelessnetworks:SysteminterconnectionWirelessLANsWirelessWANs（a）Bluetooth（b）WirelessLANHomeNetworksComputers(desktopPC,PDA,sharedperipheralsEntertainment(TV,DVD,VCR,camera,stereo,MP3)Telecomm(telephone,cellphone,intercom,fax)Appliances(microwave,fridge,clock)Telemetry(遙感，遙測)(utilitymeter（電表）,burglaralarm（防盜自動警鈴）,babycam（嬰兒監(jiān)護器）).1.3NetworkSoftwareProtocolHierarchiesDesignIssuesfortheLayersConnection-OrientedandConnectionlessServicesServicePrimitivesTheRelationshipofServicestoProtocols

ProtocolHierarchies(協(xié)議分層)Toreducetheirdesigncomplexity,mostnetworksareorganizedasastackoflayersorlevels.

Advantages

ofProtocolHierarchies:(分層的優(yōu)點)(1)Independenceoflayers:Theselayersarerelativeindependence.(各層之間是相對獨立的)(2)Ifanylayerischanged,otherlayersarenotaffected,sofarasnotchanginginterface.(靈活性好)(3)Eachlayercanberealizedinrighttechnology.(結(jié)構(gòu)上可以分割開)(4)Itiseasytorealizeandmaintain.(易于實現(xiàn)和維護)(5)Standardization(能促進標(biāo)準(zhǔn)化工作)ProtocolHierarchies(協(xié)議分層)

DefectsofProtocolHierarchies:(分層的缺點)(1)Somefunctionsmayberealizedrepeatedly.(功能重復(fù)實現(xiàn)，資源浪費)(2)Thenumberoflayerisnotcertain.(層次數(shù)難以確定)Example層次的觀點：

-每層實現(xiàn)一種特定的服務(wù)

-通過自己內(nèi)部的功能

-依賴自己的下層提供的服務(wù)機票(購買)行李(托運)旅客(出發(fā))飛機(起飛)飛行航線機票(投訴)行李(認(rèn)領(lǐng))旅客(到達)飛機(著陸)飛行航線飛行航線Example分層的空中旅行組織:服務(wù)從出發(fā)地到目的地的航線：導(dǎo)航服務(wù)柜臺-to-柜臺：“旅客+行李”票務(wù)服務(wù)行李托運-to-行李認(rèn)領(lǐng)：行李服務(wù)登機入口-to-到達出口：旅客乘務(wù)服務(wù)

跑道-to-跑道：飛機“航運”服務(wù)ProtocolHierarchies(協(xié)議分層)Protocolisanagreementbetweenthecommunicatingpartiesonhowcommunicationistoproceed.Threefactors：Syntax（語法），Semantics（語義），Synchronous（同步）

NetworkarchitectureisasetoflayersandprotocolsThedifferenceofProtocol、ServiceandSAPDesignIssuesfortheLayers(1)Amechanismforidentifyingsendersandreceivers.(2)Therulesfordatatransfer:Simplexcommunication(單工通信)

Half-duplexcommunication(半雙工通信)

Full-duplexcommunication(全雙工通信)(3)Errorcontrol(差錯控制)(4)Flowcontrol(流量控制)(5)Disassembling(分割)andgathering（合并）messages(6)Multiplexing(多路復(fù)用)anddemultiplexing(多路分用、解多路復(fù)用)(7)Routing(路由選擇)

Connection-OrientedandConnectionlessServices

TypeofconnectionServiceExampleConnection-orientedReliablemessagestreamSequenceofpagesReliablebytestreamRemoteloginUnreliableconnectionDigitizedvoiceConnectionlessUnreliabledatagramElectronicjunkmailAcknowledgeddatagramRegisteredmailRequest-replyDatabasequery連接類型服務(wù)類型應(yīng)用實例面向連接的服務(wù)可靠的消息流頁碼序列可靠的字節(jié)流遠(yuǎn)程登陸不可靠的連接數(shù)字化的聲音無連接服務(wù)不可靠的數(shù)據(jù)報電子方式的函件有確認(rèn)的數(shù)據(jù)報掛號郵件問答數(shù)據(jù)查詢ServicePrimitives(服務(wù)原語)PrimitiveMeaningLISTENBlockwaitingforanincomingconnectionCONNECTEstablishaconnectionwithawaitingpeer(對等進程)RECEIVEBlockwaitingforanincomingmessageSENDSendamessagetothepeerDISCONNECTTerminateaconnection原語含義請求request一個實體希望得到完成某些操作的服務(wù)指示indication通知一個實體，有某個事件發(fā)生響應(yīng)response一個實體希望響應(yīng)一個事件證實confirm返回對先前請求的響應(yīng)TheRelationshipofServicestoProtocolsAserviceisasetofprimitives(operations)thatalayerprovidestothelayeraboveit.Aprotocolisasetofrulesgoverningtheformatandmeaningofthepackets,ormessagesthatareexchangedbythepeerentitieswithinalayer.Protocolishorizontal,andserviceisvertical.1.4ReferenceModelsTheOSIReferenceModelTheTCP/IPReferenceModelAComparisonofOSIandTCP/IPACritiqueoftheOSIModelandProtocolsACritiqueoftheTCP/IPReferenceModel

TheOSIReferenceModelTheOSImodelhassevenlayers.Thepartitionedprinciples:(1)Alayershouldbecreatedwhereadifferentlevelofabstractionisneeded.(2)Eachlayershouldperformawelldefinedfunction.(3)Thefunctionofeachlayershouldbechosenwithaneyetowarddefininginternationallystandardizedprotocols.(4)Thelayerboundariesshouldbechosentominimizetheinformationflowacrosstheinterfaces.(5)Thenumberoflayersshouldbelargeenoughthatdistinctfunctionsneednotbethrowntogetherinthesamelayeroutofnecessity,andsmallenoughthatthearchitecturedoesnotbecomeunwieldy(龐大的).

TheOSIReferenceModelTheOSIReferenceModelThePhysicalLayer:Totransmitbits,Suchasmechanicalcharacteristic,electricalcharacteristic,timecharacteristicandfunctioncharacteristic.TheDataLinkLayer:Totransformdataframeswithouterrors.TheNetworkLayer:howtoroutefromsourcetodestination.(transmitpacket)ThetransportLayer:themostimportantlayer.Toacceptdatafromthesessionlayer,splititupintosmallerunitsifneedbe,passthesetothenetworklayer,andensurethatthepiecesallarrivecorrectlyattheotherend.TheSessionlayer:Toestablishsessionsbetweendifferentusers.(a)Asessionserviceistokenmanagement.(令牌管理)(b)Anothersessionserviceissynchronization.（同步）ThePresentationlayer:itsfunctioncontains:(a)datacompressanddecompress(b)dataencryptanddecrypt(c)dataformatTheApplicationLayer:(a)Toprovideserviceforapplicationprocedure.(b)

DataTransmissionintheOSIModel5432154321H3物理傳輸媒體數(shù)據(jù)部分?jǐn)?shù)據(jù)部分?jǐn)?shù)據(jù)部分?jǐn)?shù)據(jù)部分101比特流

11010111010T2計算機

1H5H4H2首部BUBUBUBU尾部……AP2AP1應(yīng)用程序數(shù)據(jù)計算機

2比特幀IP數(shù)據(jù)報IP分組TCP報文段UDP報文段TheTCP/IPReferenceModelTheTCP/IPReferenceModelTheHost-to-NetworkLayer(主機至網(wǎng)絡(luò)層):pointoutthatthehosthastoconnecttothenetwork.TheInternetLayer（互連層）:Packetrouting(分組路由)andavoidingcongestion（避免擁塞）.TheTransportLayer(傳輸層):end-to-endcommunication.(TCPandUDP)TCP:anreliable,connection-orientedprotocolUDP:anunreliable,connectionlessprotocolTheApplicationLayer(應(yīng)用層)

TheTCP/IPReferenceModelAComparisonoftheOSIandTCP/IPReferenceModels

TheOSI/RMdefinesthreeconcepts:Services,InterfacesandProtocols.ButtheTCP/IPdoesn’t.Connection-orientedandconnectionlesscommunication.ACritiqueoftheOSIModelandProtocols

Badtiming(糟糕的提出時機)Badtechnology（糟糕的技術(shù)）Bad