数据通信与网络cha课件

2.1,Chapter2NetworkModels,CopyrightTheMcGraw-HillCompanies,Inc.Permissionrequiredforreproductionordisplay.,2.2,2-1LAYEREDTASKS,Weusetheconceptoflayersinourdailylife.Asanexample,letusconsidertwofriendswhocommunicatethroughpostalmail.Theprocessofsendingalettertoafriendwouldbecomplexiftherewerenoservicesavailablefromthepostoffice.,Sender,Receiver,andCarrierHierarchy,Topicsdiscussedinthissection:,2.3,Figure2.1Tasksinvolvedinsendingaletter,2.4,2-2THEOSIMODEL,Establishedin1947,theInternationalStandardsOrganization(ISO)isamultinationalbodydedicatedtoworldwideagreementoninternationalstandards.AnISOstandardthatcoversallaspectsofnetworkcommunicationsistheOpenSystemsInterconnection(OSI)model.Itwasfirstintroducedinthelate1970s.,LayeredArchitecturePeer-to-PeerProcessesEncapsulation,Topicsdiscussedinthissection:,2.5,ISOistheorganization.OSIisthemodel.,Note,2.6,Figure2.2SevenlayersoftheOSImodel,2.7,Figure2.3TheinteractionbetweenlayersintheOSImodel,2.8,Figure2.4AnexchangeusingtheOSImodel,2.9,2-3LAYERSINTHEOSIMODEL,InthissectionwebrieflydescribethefunctionsofeachlayerintheOSImodel.,PhysicalLayerDataLinkLayerNetworkLayerTransportLayerSessionLayerPresentationLayerApplicationLayer,Topicsdiscussedinthissection:,2.10,Figure2.5Physicallayer,2.11,Thephysicallayerisresponsibleformovementsofindividualbitsfromonehop(node)tothenext.,Note,2.12,Figure2.6Datalinklayer,2.13,Thedatalinklayerisresponsibleformovingframesfromonehop(node)tothenext.,Note,2.14,Figure2.7Hop-to-hopdelivery,2.15,Figure2.8Networklayer,2.16,Thenetworklayerisresponsibleforthedeliveryofindividualpacketsfromthesourcehosttothedestinationhost.,Note,2.17,Figure2.9Source-to-destinationdelivery,2.18,Figure2.10Transportlayer,2.19,Thetransportlayerisresponsibleforthedeliveryofamessagefromoneprocesstoanother.,Note,2.20,Figure2.11Reliableprocess-to-processdeliveryofamessage,2.21,Figure2.12Sessionlayer,2.22,Thesessionlayerisresponsiblefordialogcontrolandsynchronization.,Note,2.23,Figure2.13Presentationlayer,2.24,Thepresentationlayerisresponsiblefortranslation,compression,andencryption.,Note,2.25,Figure2.14Applicationlayer,2.26,Theapplicationlayerisresponsibleforprovidingservicestotheuser.,Note,2.27,Figure2.15Summaryoflayers,2.28,2-4TCP/IPPROTOCOLSUITE,ThelayersintheTCP/IPprotocolsuitedonotexactlymatchthoseintheOSImodel.TheoriginalTCP/IPprotocolsuitewasdefinedashavingfourlayers:host-to-network,internet,transport,andapplication.However,whenTCP/IPiscomparedtoOSI,wecansaythattheTCP/IPprotocolsuiteismadeoffivelayers:physical,datalink,network,transport,andapplication.,PhysicalandDataLinkLayersNetworkLayerTransportLayerApplicationLayer,Topicsdiscussedinthissection:,2.29,Figure2.16TCP/IPandOSImodel,2.30,2-5ADDRESSING,FourlevelsofaddressesareusedinaninternetemployingtheTCP/IPprotocols:physical,logical,port,andspecific.,PhysicalAddressesLogicalAddressesPortAddressesSpecificAddresses,Topicsdiscussedinthissection:,2.31,Figure2.17AddressesinTCP/IP,2.32,Figure2.18RelationshipoflayersandaddressesinTCP/IP,2.33,InFigure2.19anodewithphysicaladdress10sendsaframetoanodewithphysicaladdress87.Thetwonodesareconnectedbyalink(bustopologyLAN).Asthefigureshows,thecomputerwithphysicaladdress10isthesender,andthecomputerwithphysicaladdress87isthereceiver.,Example2.1,2.34,Figure2.19Physicaladdresses,2.35,AswewillseeinChapter13,mostlocal-areanetworksusea48-bit(6-byte)physicaladdresswrittenas12hexadecimaldigits;everybyte(2hexadecimaldigits)isseparatedbyacolon,asshownbelow:,Example2.2,07:01:02:01:2C:4BA6-byte(12hexadecimaldigits)physicaladdress.,2.36,Figure2.20showsapartofaninternetwithtworoutersconnectingthreeLANs.Eachdevice(computerorrouter)hasapairofaddresses(logicalandphysical)foreachconnection.Inthiscase,eachcomputerisconnectedtoonlyonelinkandthereforehasonlyonepairofaddresses.Eachrouter,however,isconnectedtothreenetworks(onlytwoareshowninthefigure).Soeachrouterhasthreepairsofaddresses,oneforeachconnection.,Example2.3,2.37,Figure2.20IPaddresses,2.38,Figure2.21showstwocomputerscommunicatingviatheInternet.Thesendingcomputerisrunningthreeprocessesatthistimewithportaddressesa,b,andc.Thereceivingcomputerisrunningtwoprocessesatthistimewithportaddressesjandk.Processainthesendingcomputerneedstocommunicatewithprocessjinthereceivingcomputer.Notethatalthoughphysicaladdresseschangefromhoptohop,logicalandportaddressesremainthesamefromthesourcetodestination.,Example2.4,2.39,Figure2.21Portaddresses,2.40,Thephysicaladdresseswillchangefromhoptohop,butthelogicaladdressesusuallyremainthesame.,Note,2.41,Example2.5,Aswew