中文摘要：

针对分层组播中存在的公平性、分组丢失、收敛和响应速度缓慢等问题，提出一种基于多等级拥塞标记的分层组播方案LM—MCM。该方案通过引入一个多等级拥塞标记策略，使中间路由器能够根据输出端口的队列状况对流经本端口的组播分组进行标记，接收端根据标记值判断当前网络的拥塞等级，并据此进行相应的层次订阅调整，实现对网络拥塞的响应。仿真实验表明新方案能够快速收敛到最优订阅层次并逐渐稳定在该层次上；当网络发生拥塞时能够及时响应拥塞以减少不必要的分组丢失；同时LM-MCM还具有良好的会话间公平性和一定程度的TCP友好性。

英文摘要：

Layered multicast is a promising solution to address the problem of bandwidth heterogeneity of receivers in delivering live multimedia over Internet. However, schemes using layered multicast suffer from slow response time, lack of inter-session fairness and TCP-friendliness, and a lot of losses induced by slow response and failed join-experiments. A new Layered Multicast with Multilevel Congestion Marking （LM-MCM） was proposed. LM-MCM introduces a multilevel congestion marking strategy that enables a router to mark the congestion-flag field of each arriving LM-MCM packet according to the average queue size. Based on the average value of the received congestion-flags, each receiver can infer the congestion level of the bottleneck along the path, and subscribe （or unsubscribe） a layer in response to the changes of network conditions. Results of extensive simulations show it converges fast to the optimal layer of subscription, induces less loss to track the available bandwidth, and has inter-session fairness and TCP-friendliness.