摘要
在多媒体会议中 ,参与成员需要协调由谁获得向会议发送数据的权力 ,这就是发言权控制 .发言权控制是会议控制的一个重要内容 ,它直接关系到会议的服务质量 .文中通过分析发言权控制的典型交互行为 ,设计了通用发言权控制协议 (GFCP)并采用概率 CSP加以形式化描述 ,验证了协议的逻辑正确性和稳定性 .同时 ,该文还在协议实现框架中讨论了 GFCP的公平性和缩放性等问题 ,给出了相应的解决方案 .
Active members within a multimedia conference need cooperation to decide who can send data to the session, and this mechanism is called Floor Control. As one of the key factors of conference control, floor control can affect the quality of conference directly. In this paper, we propose a general floor control protocol (GFCP) based on the typical behavior abstracted from some floor control protocols in the literature. Compared with other existing floor control protocols, GFCP has three typical features: it is an application layer protocol and is independent on the underlying transport services, so it is more flexible; it is a logically correct protocol, that is, there are no live lock and dead lock within the protocol interaction behaviors; it is a reliable application protocol, although it is based on the best effort Internet services. GFCP can also be used both on concentrated cooperation applications and distributed cooperation applications. The protocol is designed to use only the basic IP service and its implementation can be integrated with conference control protocols. In order to validate the logical correctness and reliability of GFCP, we use formal method, namely communicating sequential processes (CSP), to describe the protocol behaviors. The basic CSP model proposed by Hoare is powerful enough to describe and validate the logical correctness of GFCP, but less enough to validate the reliability of GFCP. So the extended CSP, named probability CSP (PCSP), is introduced in the protocol description. We also introduce a lossy channel model in the protocol interactions to emulation a real network circumstance. And the protocol still keeps its logical correctness after the introduction of lossy model and PCSP. Finally, a simple implementation framework of GFCP based on session control and media control is proposed, and the analysis of real time, fairness and scalability are also presented.
出处
《计算机学报》
EI
CSCD
北大核心
2001年第8期845-852,共8页
Chinese Journal of Computers
基金
国家自然科学基金 (6 98730 0 8
6 9896 2 49)
教育部重点科技项目(980 46 )
国家"八六三"高技术研究发展计划 (86 3-30 6 -QN2
