Supporting Platform For Large-Scale Interactive Multimedia Applications

With the booming of the network applications, the demand for large-scale multimedia interaction becomes more and more keen. However, there exist hard limitations in this kind of implementation of its applications in WAN mainly because of the bottleneck of bandwidth. Efficient transport is the key to the problem. Furthermore, the needs become diversified with the increase of the users. We prefer to provide a general supporting platform which is more realistic and meaningful rather than the development of various applications.The author proposes and implements a supporting platform for large-scale interactive applications, which defines the point-to-point and point-to-multipoint transport interface, provides some high-level common services such as session management, user management, application management and the communication mechanism between the applications. With the loose coupling architecture, the platform is of high extensibility. Using the platform to build the new system, the developers can quickly realize their own applications and integrate them into the system easily and seamlessly.Important contribution has been made to the transport protocol which is the foundation of the platform. To satisfy the distributed property and the request of the multi-user interaction with the low network overhead and the high efficiency, multicast is the best choice. We have designed a prototype of the multicast used in WAN, which meet the main requirement as a formal supporting transport protocol such as reliability, ordering, TCP-friendliness and the supporting of large-scale participants. Furthermore,based on the theoretical analysis and applied experiment with some applications, we have thereafter achieved some improvements such as route optimization, hybrid reliability support, cross-layer congestion control, the NAT gateway crossing and the self-configuration of the topology structure.The feasibility of the platform is verified with the developing practices. A real-time multimedia interactive system is realized based on the supporting platform, which facilitated the teacher's instructive activities with about 200 participants during SARS period last year and will be used in the Tsinghua Continuing Education School. Meanwhile, some others are also involved in the testing and develop their own applications. The results indicate that the platform has high usability.Finally, the author also presents the detailed scheme of the multi-session management concerning the architecture of the supporting platform. The scheme makes it possible that the node behind the NAT gateway can be the session server and experiments have been done to verify it.