Research On Congestion Control Mechanism Based On The Video Real-time Transmission

With the appearance of MPEG-4(Moving Picture Experts Group-4)standard, the real-time transportation of MPEG-4 video has become a research hot spot. However, the recent Internet Transmission protocol also has lack of effective congestion control mechanism for the media streaming applications. Congestion control is crucial for the robustness and stability of the media streaming applications. Therefore, designing a congestion control mechanism suitable for transporting MPEG-4 video becomes important. The new mechanism must focus on both the smoothness of transmission rate of MPEG-4 real-time video stream and the TCP-friendly of guaranteeing the fair coexistence of TCP-based stream. Currently, the TCP-friendly congestion control mechanism becomes research emphasis in flow congestion control. Therefore, the thesis does some research as follows:Firstly, Combining RTP/RTCP protocol with MPEG-4 encoding standard, this thesis introduces a method to build up a framework of MPEG-4 video stream transmission system based on RTP/RTCP protocol. In the framework, UDP and TCP transmit data as the lower protocol of RTP and RTCP respectively.Secondly, this thesis discusses the developing process of TCP-Friendly congestion control algorithm, comparing and analyzing recent representative algorithm, especially the TFRC algorithm which is known as the better one in the TCP-friendly algorithm. Under the above reasons, this thesis proposes means that transplants the TFRC algorithm into the application layer of framework as a congestion control mechanism above UDP protocol.Finally, further research discovers that the control mechanism in TFRC algorithm has conflicted with minimal rate required by multimedia information transportation. According to above mentioned problem, the ER-TFRC(effective rate TFRC) algorithm has been introduced by this thesis. In the process of real-time transportation, TFRC algorithm easily results that the transmission rate is under the lowest rate required by application, which makes useless transportation. This algorithm gives the factorβto confirm the congestion degree and the standard to judge the network state during the period of network congestion and resolves how long it will take to send data under the different state of congestion to guarantee real-time video transmission and to carry out congestion control for MPEG-4 video stream.Above all of this, by analysing the TFRC algorithm and its realization, we present the ER-TFRC algorithm. It resolves the problem caused by TFRC during the congestion, which reduces the TCP-Friendly temporarily and adds the transmitted data to play real-time video normally. In present work, experiments are carried out to investigate ER-TFRC algorithm has reached expected design demand, which is better fit for MPEG-4 real-time video stream transportation.