多媒体通信系统应用子系统

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1、多媒体应用的支持系统已从本地系统发展到了分布式系统。例如公用信息查询台、多媒体电子邮件、协同工作系统、分布式虚拟现实等应用都需要高速网络、高传输率和带有适当的传输协议的通信系统。从通信角度看，我们将多媒体通信系统(MCS)分成两大子系统：应用子系统和传输子系统。多媒体通信系统Theconsiderationofmultimediaapplicationssupportstheviewthatlocalsystemsexpandtowarddistributedsolutions.Applicationssuchaskiosks,multimediamail,collabor

2、ativeworksystems,virtualrealityapplicationsandothersrequirehigh-speednetworkswithahightransferrateandcommunicationsystemswithadaptive,lightweighttransmissionprotocolsontopofthenetworks.Fromthecommunicationperspective,wedividethehigherlayersoftheMultimediaCommunicationSystem(MCS)intotwoarch

3、itecturalsubsystems:anapplicationsubsystemandatransportsubsystem.MultimediaCommunicationSystemsApplicationSubsystem应用子系统Collaborativecomputing现在工作站和PC机都配有很强的音频和视频功能,若把它们用高速网络联在一起，那么就为人们提供了一个协同计算环境，协同计算通常又称为计算机支持的协同工作(CSCW)。ThecurrentinfrastructureofnetworkedworkstationsandPCs,andtheavailab

4、ilityofaudioandvideoattheseend-points,makesiteasierforpeopletocooperateandbridgespaceandtime.Inthisway,networkconnectivityandend-pointintegrationofmultimediaprovidesuserswithacollaborativecomputingenvironment.CollaborativecomputingisgenerallyknownasComputer-SupportedCooperativeWork(CSCW).协

5、同计算CollaborativeDimensions电子化的协同工作系统可根据时间、用户范围和控制这三个参数进行分类[WSM+91]。这样协同工作系统可以被划分一个三维空间（如图11.1所示）。Electroniccollaborationcanbecategorizedaccordingtothreemainparameters:time,userscaleandcontrol[WSM+91].Therefore,thecollaborationspacecanbepartitionedintoathree-dimensionalspace(showninfigure11

6、.1).协同维数TimeSynchronousAsynchronousTelephoneTele-MentoringDesktopTeleconfereningCollaborativeSoftwareElectronicMailBulletinBoardDevelopmentCollaborativeDocumentEditingGroupScheduleManageSingleUserMultipleUsers(Group)DistributedControlCentralizedFace-to-FaceMeetingGroupCSCWConferenceRoomMee

7、tingGroupDecisionmakingUserScaleFigure11.1:Dimensionsofcollaborativecomputing.Time从图中可以看出，在时间轴上有两种模式。即同步模式和异步模式。异步协同工作说明处理活动在同时发生。Withrespecttotime,therearetwomodesofcooperativework:asynchronousandsynchronous.Thesynchronouscooperativeworkhappensatthesametime.时