Research Of The Congestion Control And QoS Of Streaming Media Transmission

Streaming media transmission becomes one of the hot spots of network applications along with the rapid development of Internet and multimedia technology. The tradition Internet can only represent characters and pictures. Streaming media totally changes the vice. It can represent not only characters and pictures, but also audio and video. Recently, the trend of the applications of multimedia presents like this: playing turning to the accessing, searching and alternative manipulation based on contents. These new-style distributing multimedia applications, which based on contents, face the problem that is how to ensure application service quality (QoS).The video coding standard MPEG-4 which used frequently in stream media transmission and the realtime transmission protocol RTP/RTCP which used in MPEG video stream transmission will be introduced in the thesis. Based on those, the factors, which affect the quality of realtime video stream transmission, will be analyzed in end-to-end system and network layer. Realtime streaming media uses UDP protocol in transport layer. It uses Open-loop Control, which has no end-to-end congestion control or uses non TCP-friendly control. The applications of realtime stream media have different QoS requirement with normal document data transmission. To sender, the sending speed should not have violent dithering. But TCP congestion control uses AIMD, which can destroy data stream smoothness. In the other way, the UDP stream, which uses non congestion control or non TCP-friendly control, will not decrease sending data when network congesion occurs. This could make bad infulence to the Internet, or even make congestion collapse.Two TCP-friendly congestion control mechanism, which are widely used, will be concluded in the thesis. They are based on explore and model congestion control. The advantages andshortcomings will also be compared. Because the scheme based on model is much more fit for streaming media transmission, some algorithms, which are all based on model, are introduced. On the base of ayalysing TFRC algorithm, an improved scheme is presented. The result of NS network simulation experiment proves that the new algorithm has sending speed smoothness and is TCP-friendly., and also can set different video objects based on user interesting according to priority. The IP network in existence can only provide Best-effort service. The service can not deal with stream media model. So, the characteristics of these two models will be simply introduced. Then we amply analyse DiffServ grouping adjustment mechanism. IETF gives some advices about service model and mechanism on the QoS in IP network. The most basal of those are IntServ and DiffServ operation grouping tag algorithm and queue management, schedule algorithm. The tag algorithms and queue management algorithms in existence have some shortcomings in MPEG video transmission, so some improvements are given considering the MPEG-4 coding characteristic. The new DiffServ algorithm and queue management algorithm can distinguish the importance of groups and can preferentially treat the important video data. The result of NS network simulation experiment proves that the improved algorithm has some help to improve the video quality.