Abstract: For wireless channels are inherently lossy, it is challengeable to maintain the Quality of Service（QOS） for live streaming. NORM（NACK Oriented Reliable Multicast） repair process uses time slot as the base mechanism, which results in long repair cycle. The feedback round algorithm is applied to optimize the repair process. This algorithm allows receiver to send NACK in rounds and sender response repair requests immediately. So that the delay for waiting response from sender is distributed to each round. Experimental results show that the protocol gets much higher performance than NORM in live streaming on wireless channel.

Key words: Negative-Acknowledgment（NACK）, NACK Oriented Reliable Multicast（NORM）, feedback round, wireless channel, live streaming

摘要： 无线网络具有高误码率和高丢失率的特点。可靠多播协议NORM使用基于时间片的反馈补偿机制，反馈周期长，不能充分利用带宽，尤其不能适用于无线网络上具有时延敏感特点的流媒体应用的要求。应用反馈轮机制优化NORM协议的反馈算法，以“轮”为单位实现NACK（Negative-Acknowledgment）控制，及时响应接收端的修复请求，将接收端等待修复的时间平均到每一轮中，有效降低了时延，且提高了带宽利用率。实验结果表明，在最大发送速率为2 Mb/s的设定下，协议在无线网络上的有效载荷吞吐量提高了0.5倍，且消除了抖动，具有低延迟的特点，更适合于流媒体传输应用的需要。

关键词: 否定应答（NACK）, 可靠多播协议（NORM）, 反馈轮, 无线网络, 流媒体