计算机网络课件 (3)

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1、Chapter2:ApplicationLayerChaptergoals:Morechaptergoals¶conceptual+¶specificprotocols:implementationühttpaspectsofnetworküftpapplicationprotocolsüsmtpüclientserverparadigmüpopüservicemodelsüdns¶learnaboutprotocols¶programmingbyexaminingpopularnetworkapplicationsapplica

2、tion-levelüsocketprogrammingprotocols哈工大计算机学院李全龙ComputerNetworks2:ApplicationLayer1Applicationsandapplication-layerprotocolsApplication:communicating,applicationdistributedprocessestransportnetworkdatalinkürunninginnetworkhostsinphysical“userspace”üexchangemessagestoi

3、mplementappüe.g.,email,filetransfer,theWebApplication-layerprotocolsapplicationüone“piece”ofanappapplicationtransporttransportnetworknetworküdefinemessagesdatalinkdatalinkphysicalexchangedbyappsandphysicalactionstakenülowerlayerprotocols哈工大计算机学院李全龙ComputerNetworks2:Ap

4、plicationLayer2Networkapplications:somejargon¶Aprocessisaprogram¶Auseragentisanthatisrunningwithinainterfacebetweenhost.theuserandthe¶Withinthesamehost,twonetworkprocessescommunicateapplication.withinterprocesscommunicationdefinedbyüWeb:browsertheOS.üE-mail:mailreader

5、¶Processesrunninginüstreamingdifferenthostsaudio/video:mediacommunicatewithanplayerapplication-layerprotocol哈工大计算机学院李全龙ComputerNetworks2:ApplicationLayer3Client-serverparadigmTypicalnetworkapphastwoapplicationpieces:transportclientandservernetworkdatalinkClient:physic

6、alrequest¶initiatescontactwithserver(“speaksfirst”)¶typicallyrequestsservicefromserver,¶forWeb,clientisimplementedinreplybrowser;fore-mail,inmailreaderapplicationServer:transportnetworkdatalink¶providesrequestedservicetophysicalclient¶e.g.,WebserversendsrequestedWebpa

7、ge,mailserverdeliverse-mail哈工大计算机学院李全龙ComputerNetworks2:ApplicationLayer4Application-layerprotocols(cont).API:applicationQ:howdoesaprocessprogramminginterface“identify”theother¶definesinterfaceprocesswithwhichitbetweenapplicationwantstocommunicate?andtransportlayerüIP

8、addressofhostrunningotherprocess¶socket:InternetAPIü“portnumber”-allowsütwoprocessesreceivinghosttocommunicatebysendingdeter