中文摘要：

QoS保证下的多播服务对于许多多媒体实时应用程序是重要的，QoS约束下的多播路由协议要求寻找连接源节点和目标节点集的支撑树使得端到端的QoS约束得以满足同时优化网络资源消耗，延迟约束最小代价树DCST是其中的关键问题．本文提出一个关于DCST的分支优化算法，该算法的核心思想是通过反向分支调节过程调整不满足QoS约束的路径并且减少对原支撑树结构的影响．仿真显示本文的算法对于实际网络是有效的．

英文摘要：

Multicast service with Quality of Service （QoS） guarantees is critical to many real-time multimedia intemet applications. The QoS-aware multicast routing protocols should have the ability to find a sourced-based tree with the end to end QoS bounds and the minimal network resource consuming. The Delay Constrained Steiner Tree problem （DCST） is one of the key issues. We present the Branch Optimization algorithm for DCST. The core of our algorithm called Reverse Branch Adjusting Procedure （RBAP） is proposed to adjust the paths violating the delay constraint at the same time keep the modification to the spanning tree as little as possible. The simulation shows that our algorithm is efficient for actual networks.