Research On Real-time Streaming Congestion Control Based On Enhanced TFRC

With the development of Internet education, Internet medical, security monitoring and AI, real-time streaming has been widely used in various situations. How to provide high quality video stream at a smooth rate is the key point of research on real-time streaming system.The related technologies of traditional wired network real-time streaming system, such as RTP/RTCP transmission protocol, H.264 over RTP, are introduced in the beginning. Then the limitations of using TCP in streaming transmission is discussed to explain why TCP is not suitable for real-time streaming system. After that, the congestion control mechanisms that often used in streaming system based on UDP is introduced, as well the new problems these mechanisms faced in wireless network environment. As a kind of traditional congestion control mechanism, TFRC not only provide effective control, and also ensure the smoothness of transmission rate. But there are some disadvantages in TFRC, among them, the performance degradation during slow start stage and the inapplicability in wireless network is the key point of this thesis.Firstly, performance simulations of TFRC under wired and wireless network is made. The simulation results show the underlying reasons of two problems above is the rate double during slow start stage and the inability of distinguish the type of packet loss in wireless environment. Then the method used in TCP's initial window is introduced to calculate initial rate. Then ROTT is proposed as a reference to both congestion avoidance and loss packet type judging. Compared to the original TFRC mechanism, the enhanced mechanism perform a more smooth transmission rate, especially in wireless network.The congestion control mechanism framework meet some problems when used in real application, some of them come from the adaption, others depend on the characteristics of actual business. The last part of this thesis come up with a real-time streaming prototype system which based on RTP/RTCP protocol, combined with H.264 stream and the enhanced mechanism.