摘要： 提出了一种在分层视频组播应用中，组播源能根据组播应用类型选择最优层速率的方法，目的是提高组播组的全局视频质量。考虑到组播应用类型的不同，该文给出了一个全局质量因子(GQI)，反映了接收端的满意程度(接收端总的视频质量下降程度)，组播组占用的网络带宽和接收端视频质量的稳定性。这些指标可根据组播应用类型的不同进行调整。仿真验证，在使用GQI 作为衡量组播组全局视频质量的标准时，能够保证所要优化的目标，达到用户的需求。

关键词: 组播；分层组播应用；全局视频质量

Abstract: This paper addresses the problem of choosing the optimal layer rate according to the type of multicast applications in multi-layeredmulticast applications to improve global video quality. Due to various types of applications, it introduces a global quality index (GQI) thatcharacterizes the density of satisfied receivers (the degradation at the receivers), the amount of allocated network bandwidth and the stability of thequality of the receivers. These metrics compose the unified metric GQI that can be adjusted according to the type of the multicast applications.Simulation results show that using this index, the user’s objective can be achieved.

Key words: Multicast; Multi-layered multicast application; Global video quality