The Research Of Adaptive Network Transmission Control Technology And The Application In Video Conferencing System

With the widespread use of the computer network, the demands for high quality of online multimedia services are ever increasing. Although the bandwidth is trending to gradual increase for the improvement of technology, it is not enough to provide satisfied quality of services at the present time yet.Usually, bandwidth needed by transmission of multimedia data, especially video, is exceeding the throughput of network providing. Video frame will be dropped when the network experiences congestion. The performance of data transmission may therefore be affected seriously. How to improve the quality of service for multimedia data on condition of bandwidth limit is the hotspot of research in multimedia application field recently.There were many researches focusing on point-to-point congestion control based on TCP. Studies of congestion control in multicast are still in experiment phase. Hardly is there any congestion avoidance control used in most multicast applications.In this paper, firstly, existing network congestion control mechanisms are studied and some shortages of current control mechanism in multicast environment are pointed out. Then a network transfer feedback-control model is established. Based on this model, an application level layer-based congestion avoiding mechanism using by multicast is given. It takes advantage of layered video coding, sets down a set of video transfer scheme with different bandwidth. Close-loop feedback control allows receivers to select one of scheme automatically according to the network status carried back by the feedback information. Also, a protocol is presented in order to make the mechanism standardized.In this research, simulation software is taken to evaluate the algorithm's performance. Results demonstrate that the control mechanism can tolerate occasional bandwidth changes in the presence of transient network congestion.Then, this adaptive control mechanism is implemented in videoconference system. Corresponding system architecture and software framework are designed at the same time. The process of implement the given mechanism is described and algorithm both in sender and receiver are carried outFinally, the conclusions of the mechanism and the future trends of study are given.