Multicast Congestion Control Related Issues

With the springing up of real-time services, such as VOD (Video on Demand), video conferencing, distance learning, network interaction game, multicast is considered to one of the widely used technologies. But multicast based on UDP cannot offer congestion control. At the present time, that existing TCP applications, as the main applications in the Internet, offer congestion control have made it important to ensure the fairness when multicast coexists with TCP protocols. Therefore study of congestion control about multicast is becoming an important subject.The paper solves three problems of multicast congestion control: quickly response to network congestion, feedback suppressed and fairness of protocol.Firstly, aiming at quickly response to network congestion, the paper analyses some existing active queue management algorithm and brings forward a new algorithm. When average length of queue exceeds a reference value, the algorithm adjusts the rate of packet loss percentage according to the packet arriving rate. Its queue length keeps around the reference value, so it has more stability and self-adaptability to network congestion.Secondly, taking feedback implosion into account, the paper uses the active network technique for improving router's functions and brings forward a kind of congestion control that is concerned with the router, which implements feedback aggregation and local recover of lost packet. Having been simulated and analyzed, the algorithm has been testified to have better scalability and utilization of bandwidth.Thirdly, aiming at fairness of protocol, the paper, based on the existing TCP-Friendly Multicast Congestion Control (TFMCC), considers the problem of the dithering of transmission rate when the multimedia stream is transferred, and proposes an improved algorithm. The improved algorithm adjusts its transmission rate according to the probability of packet loss and TCP-friendliness, and smoothes its rate adaptation. The algorithm can preferably alleviate the dithering of transmission rate and ensure intra-protocols fairness and meet TCP-friendliness.Finally, NS, a widely used network simulation tool, is used to analyses and validates the performance of forenamed algorithms.