《计算机网体系结构》PPT课件

1、,第三章：计算机网体系结构OSI模型&TCP/IP协议组,胡建伟,协议与体系结构,硬件和软件相结合的分层结构，用于支持系统之间的数据交换以及分布式应用。在协议结构的每一层，通信系统都要实现一个或多个通用协议。协议所执行功能：封装，分段，重组，连接控制，顺序控制，流控制，差错控制，寻址以及复用。开放系统互连（OpenSystemInterconnection）最广泛的协议TCP/IP协议组。,ProtocolCharacteristics,Directorindirect(直接间接)Monolithicorstructured(整体化结构化)Symmetricorasymmetric(对称？)S

2、tandardornonstandard(标准？),DirectorIndirect,DirectSystemsshareapointtopointlinkorSystemsshareamulti-pointlinkDatacanpasswithoutinterveningactiveagentIndirectSwitchednetworksorInternetworksorinternetsDatatransferdependonotherentities,LINK,MonolithicorStructured,CommunicationsisacomplextaskToocomplexfo

3、rsingleunitStructureddesignbreaksdownproblemintosmallerunitsLayeredstructure,Whyalayerednetworkmodel,Itbreaksnetworkcommunicationintosmaller,simplerparts.Itstandardizesnetworkcomponentstoallowmultiple-vendordevelopmentandsupport.Itallowsdifferenttypesofnetworkhardwareandsoftwaretocommunicatewitheach

4、other.Itpreventschangesinonelayerfromaffectingtheotherlayers,sothattheycandevelopmorequickly.Itbreaksnetworkcommunicationintosmallerpartstomakelearningiteasiertounderstand.,SymmetricorAsymmetric,SymmetricCommunicationbetweenpeerentitiesAsymmetricClient/server,LINK,StandardorNonstandard,Nonstandardpr

5、otocolsbuiltforspecificcomputersandtasksKsourcesandLreceiversleadstoK*Lprotocolsand2*K*LimplementationsIfcommonprotocolused,K+Limplementationsneeded,UseofStandardProtocols,ProtocolFunctions,Encapsulation封装Segmentationandreassmebly分段和重组Connectioncontrol连接控制Ordereddelivery顺序发送Flowcontrol流控制Errorcontro

6、l差错控制Addressing寻址Multiplexing复用Transmissionservices传输服务,Encapsulation,AdditionofcontrolinformationtodataAddressinformationError-detectingcodeProtocolcontrol,LINK,Segmentation(Fragmentation),DatablocksareofboundedsizeApplicationlayermessagesmaybelargeNetworkpacketsmaybesmallerSplittinglargerblocksint

7、osmalleronesissegmentation(orfragmentationinTCP/IP)ATMblocks(cells)are53octetslongEthernetblocks(frames)areupto1526octetslongCheckpointsandrestart/recovery(断点检查,重启动/恢复),LINK,WhyFragment?,AdvantagesMoreefficienterrorcontrolMoreequitableaccesstonetworkfacilitiesShorterdelaysSmallerbuffersneededDisadva

8、ntagesOverheadsIncreasedinterruptsatreceiverMoreprocessingtime,ConnectionControl,ConnectionEstablishmentDatatransferConnectionterminationMaybeconnectioninterruptionandrecoverySequencenumbersusedforOrdereddeliveryFlowcontrolErrorcontrol,ConnectionOrientedDataTransfer,OrderedDelivery,PDUsmaytraversedi

9、fferentpathsthroughnetworkPDUsmayarriveoutoforderSequentiallynumberPDUstoallowforordering,LINK,PDUProtocolDataUnit,FlowControl,Donebyreceivingentity(接收实体执行)Limitamountorrateofdata(数据量,速率)Stopandwait(最简单的停-等式流控)Creditsystems（信用关系）Slidingwindow(没有收到确认前能发送的最大量)Neededatapplicationaswellasnetworklayers,E

10、rrorControl,GuardagainstlossordamageErrordetectionSenderinsertserrordetectingbitsReceiverchecksthesebitsIfOK(),acknowledgeIferror(),discardpacketRetransmissionIfnoacknowledgeingiventime,re-transmitPerformedatvariouslevels,Addressing,Addressinglevel(寻址级别)Addressingscope(寻址范围)Connectionidentifiers(连接标

11、识符)Addressingmode(寻址方式),Addressinglevel,RefertothelevelincommunicationsarchitectureatwhichanentityisnamedUniqueaddressforeachendsystem(computer)androuterNetworkleveladdressIPorinternetaddress(TCP/IP)NetworkserviceaccesspointorNSAP(OSI)ProcesswithinthesystemPortnumber(TCP/IP)ServiceaccesspointorSAP(O

12、SI),AddressConcepts,AddressingScope,Globalnonambiguity（全局无二义性）GlobaladdressidentifiesuniquesystemThereisonlyonesystemwithaddressXGlobalapplicability（全局可应用性）Itispossibleatanysystem(anyaddress)toidentifyanyothersystem(address)bytheglobaladdressoftheothersystemAddressXidentifiesthatsystemfromanywhereon

13、thenetworke.g.MACaddressonIEEE802networks,202.117.112.34,ConnectionIdentifiers,Connectionorienteddatatransfer(virtualcircuits)AllocateaconnectionnameduringthetransferphaseReducedoverheadasconnectionidentifiersareshorterthanglobaladdressesRoutingmaybefixedandidentifiedbyconnectionnameEntitiesmaywantm

14、ultipleconnections-multiplexingStateinformation,LINK,AddressingMode,UsuallyanaddressreferstoasinglesystemUnicastaddress（单播地址）SenttoonemachineorpersonMayaddressallentitieswithinadomainBroadcast（广播地址）SenttoallmachinesorusersMayaddressasubsetoftheentitiesinadomainMulticast（组播地址）Senttosomemachinesoragro

15、upofusers,Multiplexing,SupportingmultipleconnectionsononemachineMappingofmultipleconnectionsatoneleveltoasingleconnectionatanotherCarryinganumberofconnectionsononefiberopticcableAggregatingorbondingISDNlinestogainbandwidth,LINK,复用（一对一，上行，下行）,高层连接,低层连接,上行复用：一条低层连接向数条高层连接提供服务,TransmissionServices,Prio

16、rity（优先级）e.g.controlmessagesQualityofservice（服务等级）MinimumacceptablethroughputMaximumacceptabledelaySecurity（安全性）Accessrestrictions,OSI-TheModel,AlayermodelEachlayerperformsasubsetoftherequiredcommunicationfunctionsEachlayerreliesonthenextlowerlayertoperformmoreprimitivefunctionsEachlayerprovidesserv

17、icestothenexthigherlayerChangesinonelayershouldnotrequirechangesinotherlayers,PrinciplesusedindefiningtheOSIlayers1,Donotcreatesomanylayersastomakethesystemengineeringtaskofdescribingandintegratingthelayersmoredifficultthannecessary.Createaboundaryatapointwherethedescriptionofservicescanbesmallandth

18、enumberofinteractionacrosstheboundaryareminimized.Collectsimilarfunctionsintothesamelayer.Createseparatelayerstohandlefunctionsthataremanifestlydifferentintheprocessperformedorthetechnologyinvolved.,PrinciplesusedindefiningtheOSIlayers2,Allowchangesoffunctionsorprotocolstobemadewithinalayerwithoutaf

19、fectingotherlayers.Selectboundariesatapointwhichpastexperiencehasdemonstratedtobesuccessful.Createalayerwhereitmaybeusefulatsomepointintimetohavethecorrespondinginterfacestandardized.Createalayerwherethereisaneedforadifferentlevelofabstractioninthehandlingofdata.Createforeachlayerboundarieswithitsup

20、perandlowerlayeronly.,物理层,数据链路层,网络层,传输层,会话层,表示层,应用层,OSIasFrameworkforStandardization,LayerSpecificStandards,ElementsofStandardization,Protocolspecification（协议规约）OperatesbetweenthesamelayerontwosystemsMayinvolvedifferentoperatingsystemProtocolspecificationmustbepreciseFormatofdataunitsSemanticsofallf

21、ieldsallowablesequencenumberofPDUsServicedefinition（服务定义）FunctionaldescriptionofwhatisprovidedAddressing（寻址）ReferencedbySAPs,ServicePrimitivesandParameters,Theservicesbetweenadjacentlayersareexpressedintermsofprimitivesandparameters.Aprimitivesspecifiesthefunctiontobeperformed.Aparameterisusedtopass

22、dataandcontrolinformation.Theactualformofaprimitivesisimplementation-dependant.,Serviceprimitivetypes,Timesequencediagramsforserviceprimitives,Serviceuser(LayerN),Serviceprovider(LayerN-1),Serviceuser(LayerN),x.request,x.indication,x.response,x.conform,data,para,(N-1)PDU,data,para,(N-1)PDU,CONFIRMED

23、SERVICEONLY,AnexchangeusingtheOSImodel,物理层,比特流,Physicallayer,Coordinatethefunctionsrequiredtotransmitabitstreamoveraphysicalmedium.PhysicalcharacteristicsofinterfacesandmediaRepresentationofbitsDatarateSynchronizationofbitsLineconfigurationPhysicaltopologyTransmissionmode,数据链路层,Framing,Physicaladdressing,Flowcontrol,Errorcontrol,Accesscontrol,Figure2-14,数据链路层举例,Figure2-6,网络层,LogicalAddressing,Routing,网络层举例,Figure2-7,传输层,Service-pointAddressing,Segmentationandreassembly,Connectioncontrol,Errorcontrol