中文摘要：

提出一种基于集中控制与分布式自组织相结合应用层组播方案：CD-Media．这种多层次的、稳定的组播方案在上层由能力较强且稳定的专用服务器组成星形结构，并由它们集中控制下层Mesh结构和组播树的构造与维护．下层应用层拓扑采用分布式的自组织协议．该方案分超节点、Cluster和组播岛3个层次，它们共同组成一棵组播树．这种“分层”、“分群”的思路提高了可扩展性，最大化提高网络可支持的用户数量，降低了成本，非常适合网络电视这种单源准实时应用．此外，为解决网络电视对稳定性要求高和应用层网络动态变化大之间的矛盾，Cluster内的应用层组播成员间采用全连通的Mesh结构，在此基础上由超节点集中计算组播树．CD-Media还将应用层组播与网络层组播相结合、充分发挥两者的优势．实验评价了CD—Media的性能，并与已有算法进行比较，结果显示该方案具有明显的优点．

英文摘要：

An application layer multicast mechanism, CD-Media, is proposed based on the combination of central-control and distributed self-organization. This mechanism with different hierarchies is stable and suitable for the quasi-real-time application. Special servers with high performance is deployed in the higher levels to organize the star topology, and they are responsible for the construction and maintenance of Mesh network and multicast tree in the lower levels. In the lower levels a distributed protocol for self-organization is used and Mesh-first strategy is adopted in the Cluster. Multicast technologies both in application layer and network layer are combined to make use of their own advantages to achieve higher performance. An experiment is delicately designed to show the advantage of CD-Media, and it is convinced that it will be a promising mechanism in overly multicast.