层次化可扩展可靠组播研究及其在分布式组播发言权控制中的应用

【作者】 潘晏涛；

【导师】 吴玲达； 王晖；

【作者基本信息】 国防科学技术大学 ， 管理科学与工程， 2002， 硕士

【摘要】 当今，多媒体会议正向着基于IP组播的大规模、大范围、分布式的方向发展。但是由于组播传输是不可靠的，所以难以实现基于组播的会议控制。其结果是现有的会议系统或者保持传统的集中式会议控制结构，只将组播技术用于向没有交互权的接收者发送媒体数据；或者放弃会议控制，将组播技术应用于小规模松散型交互。目前，组播技术的这两种应用方式都不能很好地发挥它给多媒体会议带来的在可扩展性和鲁棒性方面的巨大提升潜力。因此组播会议也就达不到它所应具有的可扩展性。为了解决这个问题，我们提出基于可靠组播实现分布式会议控制，其核心是设计适合分布式组播会议控制的可靠组播通信模型。本文从分布式组播会议控制对网络通信的要求出发，在对影响可靠组播性能的因素进行深入分析基础上，融合现有可靠组播协议的优秀思想，提出了一个新的基于接收方丢失报文概率分组的层次化可扩展可靠组播通信模型HSRM(Hierarchical Scalable Reliable Multicast)。并根据“分布”、“动态”、“公平”、“自治”等原则，设计了HSRM层次化结构的动态构建和维护机制，最后将它与三个经典可靠组播协议进行了比较。HSRM使用全分布方式和一致的组播通信构造与发送者无关的层次结构，限制了反馈和修复报文的扩散范围并减小了组内节点的异构性和组播组的规模。在保持良好的可扩展性、鲁棒性和灵活性的前提下，提高了多对多可靠组播的性能。在HSRM的基础上，我们结合基于IP组播的协同学习环境WebLearning+的应用需求，设计了一个分布式组播发言权控制工具。该工具协议一致，支持灵活的会议结构，失效恢复简单，支持与会者自由加入和退出，有很好的可扩展性和鲁棒性。 本文的贡献体现在以下几个方面： 1．提出了一个新的面向分布式组播会议控制的可靠组播通信模型HSRM。 2．通过理论分析和数值实验，研究了影响可靠组播性能的主要因素及其影响程度和变化规律。其结果对于正确建立层次化可靠组播模型分组的原则具有普遍意义。 3．设计了动态构建和维护HSRM层次化结构的分布式、自适应算法，对构造其它层次化可靠组播模型具有一定程度的借鉴意义。 4．设计了一个基于可靠组播协议HSRM的分布式组播发言权控制工具。更多还原

【Abstract】 In recent years,the multicast-based conference that includes a large number of hosts and covers a large scope of network is the main development direction of the multimedia conferencing. However,IP multicast is generally unreliable,disordered and with redundant copies,and there is no reliable multicast protocol designed for multicast-based conference control. As a result,it is quite difficult to realize conference control basing multicast. As to the existing multicast-based conference systems,two choices are widely adopted:to keep the traditional centralized conference control structure with multicast only used for sending media data to those receivers who can’t interact with others;or to give up conference control at all with multicast used for interactive loosely coupled sessions including a small quantity of hosts. Neither of the two choices can take the advantages of multicast to improve the scalability and robusticity of multimedia conferencing actually. In order to solve this problem,a reliable multicast communication model for conference control is designed specially. We firstly study the requirements of multicast-based conference control,then analysis the main factors to the performance of reliable multicast. Subsequently we present a new reliable multicast protocol named HSRM (Hierarchical Scalable and Reliable Multicast) according to the receivers’ packet loss probabilities. Furthermore,we present a distributed self-adaptive mechanism to construct and maintain the hierarchical structure of HSRM dynamically according to a series of criterions such as distributed,dynamical,fair and so on. At last,the comparisons to several well-known multicast protocols SRM,RMTP and TMTP are given. HSRM constructs hierarchical structure basing multicast communication completely and its structure has no relationship with the senders. The spread of feedback and recovery packets are restricted efficiently. The heterogeneity and the size of multicast sub-groups are also decreased. In a word,the performance of the multipoint-to-multipoint reliable multicast is improved,without bad effect on the robusticity,scalability and flexibility. We then present a HSRM-based distributed floor control model to accommodate the application background of WebLearning+,an IP-multicast based collaborative learning system. This floor control model is flexible,scalable and robust. It supports late joining,early leaving and crash recovery.更多还原