多媒体通信系统　.pptVIP

　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。 The consideration of multimedia applications supports the view that local systems expand toward distributed solutions. Applications such as kiosks, multimedia mail, collaborative work systems, virtual reality applications and others require high-speed networks with a high transfer rate and communication systems with adaptive, lightweight transmission protocols on top of the networks. From the communication perspective, we divide the higher layers of the Multimedia Communication System(MCS) into two architectural subsystems: an application subsystem and a transport subsystem.  Application Subsystem Collaborative computing 　 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)。 The current infrastructure of networked workstations and PCs,and the availability of audio and video at these end-points,makes it easier for people to cooperate and bridge space and time. In this way, network connectivity and end-point integration of multimedia provides users with a collaborative computing environment. Collaborative computing is generally known as Computer-Supported Cooperative Work (CSCW). Collaborative Dimensions　 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）。 Electronic collaboration can be categorized according to three main parameters: time, user scale and control [WSM+91]. Therefore, the collaboration space can be partitioned into a three-dimensional space (shown in figure 11.1). 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。 With respect to time ,there are two modes of cooperative work: asynchronous and synchronous. The synchronous cooperative work happens at the same time. User Scale 用户轴上的参数说明是否为单用户协同工作，或者是两个用户以上的组与另一组协同工作。 The user scale parameter specifies whether a single user collaborates with another user or a group of more than two users coll