主动可靠组播传输往返行程时间估算策略

针对可靠组播传输提出了一种基于主动式网络的往返行程时间（Rount Trip Time，简称RTT）估算策略。与传统的RTT估算策略相比，这一策略不要求组播组成员之间保持时钟同步，它能够精确也确定组播树中各成员到组播源之间的往返行程时间，及时地响应网络组播结点及链路的动态变化。可靠组播传输协议借助这一策略可以有效地减少网络中不必要的控制消息，根据网络环境及时准确地确定进入网络的数据包速率，从而提高整个组播组的吞吐量。利用计算机网络仿真平台实际研究了RTT估值策略在主动可靠组播传输协议中的实际性能，与传统的基于否定确认的可靠组播协议进行了比较，仿真结果证实了它所具备的良好特性。

Round trip time estimation scheme in active reliable multicast transport

This paper proposes a Round Trip Time(RTT) estimation scheme of reliable multicast transport based on Active Networks. Compared with traditional RTT estimation schemes, this scheme can precisely estimate the round trip time between the sender and receivers of multicast group, rapidly react to the dynamic topology change and does not require clock synchronization among group members. With this scheme, reliable multicast transport protocol could greatly reduce unncessary multicast control messages, precisely decide the packet sending rate of multicast group and consequently increases the average throughput of the multicast group. Computer simulations are given to analyze the performance of this RTT estimation scheme in the Active Reliable Multicast Transport protocol and compare it with traditional NAK based reliable multicast transport protocols, with the result of simulation proving the advantage of this scheme.