The Study And Realization Of The Overlay Network Based Application Level Multicast System

Nowadays multimedia applications, such as media flows, video conference and video on demand are used more and more widely. Traditional unicast technology can hardly meet this kind of applications well, so people begin research on multicast technology to solve the problem of transmitting redundant data. Especially for the audio and video applications, it can save a large number of network resources. Up to now, unsolved issues in IP multicast service model and protocol prevent it from widely deployment at Internet. Then people turn to other alternative technologies, among which is application level multicast. In application level multicast, multicast functions are moved from routers to end systems. It is end systems'duty to fulfill group and membership management, duplicating and distributing data packets. All group members set up an overlay network on top of IP network and construct multicast tree in it.The research of the thesis focuses on the application level multicast system. In the thesis, a new multicast protocol is proposed, simulated and a prototype is designed and realized. The following are the detailed content:Study on the existing application level multicast systems, analyze their characteristics, vantage and problems and then fix on the topic and research content of the thesis.Research on the application level multicast architecture. Discuss the advantage of the Client-Multicast Server structure: for example, it can be more easily deployed at Internet; it improves the scalability of the system; Allowing only nodes which are more stability and have more transmit bandwidth to join the multicast tree can avoid the performance bottleneck. A new application level multicast protocol-ALMP is proposed, which can be applied to real-time applications. Root of the multicast tree keep record of the whole tree, which helps nodes join and leave effectively. Different from most of existing systems, nodes in ALMP can have different requirement bandwidth. ALMP tries to minimize the delay from root to receivers, while satisfying the bandwidth constraint. And ALMP implements a formula to compute the priority of the potential parent. Through controlling the size of set of potential parents according to the priority, ALMP can reduce the join cost.Simulation on ALMP. Using relative delay penalty and join cost of the multicast tree as the metric, simulation proves the correctness of ALMP.Realization of an application level multicast prototype- ALMS. ALMS adopts the client-multicast server structure, implements ALMP as its multicast protocol, denotes users'different QoS requirement using XML technology and transmits video files using JMF tool suite.Test about ALMS. The test result of every module of ALMS shows that it can work well and provides customizable service according to users'own requirement.The research work in the thesis is affiliated with the national science foundation project"Research on the Next Generation Network Service Architecture and its Key Technology".