Research On Congestion Control Strategy In Video Streaming Adaptive Transmission

With the continuous development of communication technology and multimedia technology, the application of video streaming becomes more and more widely. There is an obvious phenomenon that the majority of data services based on TCP transmission in the current network, which uses TCP's own congestion control mechanism to adjust the transmission rate to ensure the quality of service. However, in the practical application of video streaming, UDP is used to transmit the data. But UDP protocol lacks congestion control scheme. When there is congestion it will not only occupy lots of TCP bandwidth but also bring more serious congestion. Therefore, it is necessary to research the congestion control strategy which is suitable for video streaming and shares the bandwidth with TCP stream.Firstly, this paper analyzes the principle and main content of network-based and terminal-based congestion control mechanism. And also study the advantages and disadvantages of them, according to the characteristics of video streaming transmission. Due to the high requirement of delay, jitter and stability of video stream transmission, this paper mainly analyses the TFRC(TCP-Friendly Rate Control) algorithm. Secondly, analyzes the shortages of TFRC algorithm existing in the current application, mainly displays in: the slow start stage of TFRC uses the loss of the packet as the only signal to end this stage, which causes a large number of data packets to be lost in later stage; In the congestion avoidance stage, the throughput formula ignores the changes of the round-trip time delay, which is the lack of control of the stability of the transmission rate. Finally, according to the shortcomings existing in TFRC and combining with the characteristics of video transmission, this paper presents an improved TFRC protocol named I-TFRC(Improved-TFRC). In the slow start stage, I-TFRC made delay jitter as a warning signal of impending congestion in the network,to reduce the number of packet loss. In the congestion avoidance stage, the round-trip time jitter proportion is used as a response feedback of network's state to modify the sending rate of TFRC, which is used to reduce the available throughput of the calculated, thereby reduce thesending rate fluctuation, and make the network video streaming transmission more stable.Finally, using the NS2 network simulation platform for experiment, validate the improved algorithm in rate smoothness, packet loss rate, delay and delay jitter. The experimental results show that I-TFRC has significantly improved in these aspects, more suitable for video transmission.