The ever-increasing multicast data applications recently have aroused considerable interests in the design of congestion control scheme for multicast services. This kind of study is indeed important, especially to those multicast receivers with large propagation delays which mean the feedbacks arriving at the source node are somewhat outdated and harmful to control actions. A distributed self-tuning explicit rate algorithm is presented in this paper to overcome the vulnerability that suffers from the heterogeneous multicast receivers. It is suggested that congestion controllers be located at the source and the participating intermediate nodes to regulate the transmission rate. This network-assisted property is different from the traditional control scheme in that the router computes the appropriate transmission rate of itself and executes it rather than sends packets in best efforts. This active manner makes the control more responsive to the network status. The proposed self-tuning controller has essentially a proportional controller structure. The proportional gain is related to the extent that the router buffer occupancy deviates from the desired point. Simulation results show the efficiency of the proposed scheme in terms of fast response, high link utilization, and relatively stable buffer occupancy.%拥塞控制是组播服务需要解决的重要问题.当存在大量异质的、传播时延较高的组播接收者时,到达源端的反馈在一定程度上已经过时,因此常常严重影响控制效果.提出了一种分布式、自调节的显式速率比例控制方案,它在源端和中间节点实施控制算法调整各自的发送速率,并且比例控制系数会根据路由器缓冲区占有量偏离理想值的程度自动调节.这种网络参与控制的主动行为比传统路由器尽力服务的工作方式对网络状态的响应更加迅速,自调节的控制系数比固定的控制系数更能及时调节发送速率.仿真实验结果表明,算法具有响应快,链路利用率高和路由器缓冲区占有量比较稳定的特性.
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