The Research On Layered Multicast Congestion Control Scheme For Wireless Network

With the development of multicast-based multimedia applications and wireless network in recent years, the dynamic and heterogenetic of the network takes more and more important roles in those applications. Layered multicast is recognized as the best technique for solving dynamics and heterogeneousness of the network in multicast environment. Aimed at the layered multicast transmit protocol which suits for multimedia transmition, havs congestion control mechanism, and can fairly share bandwidth with TCP protocol in Wireless network, and based on our research on current congestion control arithmetic, this paper present an congestion control for layered multicast application based on wireless network (WALM, Wireless Adaptive Layered Multicast). The algorithm can be divided into three parts:First is network congestion estimation. The network congestion estimation is the base of congestion control scheme. Because of the character of wireless network, we can't use packet's loss as the semaphore of network congestion. Contrapose to the disadvantage of using Round Trip Time in currently research results, we use the trend of one way delay. In company with Pathload arithmetic to determine the network congestion, the accuracy of congestion detection can be guaranteed.Second is rete control problem. Because the transmit rate of multimedia data should be smoothly and with no acute change, otherwise it will affect the user-perceived quality. This paper propose a danamic parameter mechanism of rate control, and the corresponding settlement, guarantee the transmit speed's smoothly on the condition of the TCP friendly.The third is the feedback control problem. As in large multicast group, feedback allways affect the protocol's expansibility directly. It should alleviate the contradiction between the sender's adaptability and receiver's feedback frequency. We propose a receiver-driven scheme, avoid feedback problem successfully, thereby we ensure the expansibility of protocol.Simulation is done in ns2 network simulator and results are analysed, it shows that WALM suits wireless network very well, It's obtain good performance in high bit error ratio wireless network environment, and it's a TCP friendly protocol over low bit error ratio environment; also the accuracy of congestion detection is guaranteed, and the congestions happened in reverse link are ignored successfully.