Research And Application Of Stream Media Transmission Congestion Control

With the continuous development of the Internet and wireless network, the stream media technology has been applied widely in related fields. A number of real-time services adopt UDP protocol at transport layer currently. The amount of information which is transmitted through UDP would increase quickly as large of stream media applications appearing on the Internet. Compared with TCP, UDP has a smaller time cost and does not guarantee to deliver the packet to destination correctly. Due to the features above, most stream media application generally adopt UDP. As result of lack of congestion control mechanism, UDP flow would have more chance to occupy channel than TCP, which makes the TCP flow obtain less network resources. DCCP(Datagram Congestion Control Protocol)is proposed by IETF to substitute for the UDP on the transport layer. Based on the features of real-time businesses, it combines the advantages of UDP and TCP friendly rate control mechanism. At the same time, DCCP contains multiple congestion solving strategies that could be adopted according application.Not only the congestion control mechanism but also a stable throughput is needed in the transporting process of stream media to guarantee better quality of service. TFRC is a friendly TCP congestion control protocol oriented stream media transport. It is widely recognized in stream media application because of its good performance. The main work done in the paper could be listed as follow:①Summarizes the popular network protocols used in stream media transmission, and analyzes the advantages and disadvantages of sevral transport layer protocols, and points out the shortages of congestion based on UDP in application layer.②On analysising the theory of TFRC, the paper does some improvements to the TFRC's congestion strategies which could not guarantee the minimum rate to meet the requirements of stream media application when the congestion occurs, and designs a more reasonable congestion control mechanism.③Redesigning an existed stream media system to use DCCP and improved TFRC. This paper states the relationship between application layer protocols and DCCP, and dicusses the adaptive buffer size, framing mechanism and the synchronization algorithm betwen audio and video.④Finally, a couple of experiments have been done based on the old and new stream media system. The results from experiments show that the new schema can guarantees better quality of service.