支持VCR功能的扩展流合并算法VCRSM的设计与实现

多播传输作为视频点播服务的一个有效方法在近十年来被广泛研完，许多算法都相对成熟。但由于VCR操作会使多播调度的复杂度增加，性能降低，因此对支持用户VCR操作的多播调度算法的研究很少。针对该问题，本文提出了一个支持VCR功能的零时延流合并调度算法VCRSM。VCRSM通过在客户端使用主动缓存技术满足部分VCR操作，并在服务器端对普通流合并算法进行扩展，使之能响应VCR请求流，并通过延迟请求提高流的共享度，优化服务器的性能。模拟实验证实，VCRSM能在不占用更多带宽的情况下，零延迟地满足用户的各种VCR操作。

Design and Implementation:An Algorithm Supporting VCR Functions by Extended Steam Merging

As an effective means of VOD service,multicast has been researched for about ten years. Many algorithms of it have been matured. But there are only a few papers about multicast schedule supporting VCR functions. The rea- son is that supporting VCR functions will increase the complexity of schedule of the server,and will decrease its capa- bility. In this paper,we present a rnulticast scheduling algorithm VCRSM provding VCR functions by extended stream merging. Active buffer management on client is used to partly satisfy the VCR actions of users. On server,original stream merging is modified to adapt to all VCR requests. We also put forward delay request to optimize the server's performence. When compared with other systems in simulation,VCRSM can satisfy all kinds of VCR functions with no delay,while occupying no more bandwidth than others.