P2P流媒体Cache的置换算法

Replacement Solutions for Streaming Cache on P2P Network

P2P流媒体cache是一种有效减少带宽开销、提高对象利用率的技术,通常采用FIFO,LRU等算法置换内容.然而,流媒体不同于Web对象,P2P网络也有别于客户/服务器模式.在分布式应用中这些算法可能影响系统的性能,为此,分析了FIFO和LRU置换算法,提出了基于供求关系的SD算法,以及基于分片副本数量的REP算法,并对其进行评估和比较.针对不同的节点到达间隔,将SD和REP同FIFO,LRU进行比较,发现在启动延迟、媒体副本数量和根节点依赖度方面SD和REP几乎均优于FIFO和LRU.同LSB(least sent bytes)算法相比,某些场景中SD的启动延迟减少了约40%,而REP在副本数量方面远远超过LSB的结果,说明在P2P网络流媒体服务中使用SD和REP缓存置换算法有助于提高系统性能.

Peer-to-peer streaming cache is employed widely as it can reduce the bandwidth usage and improve the utilization of objects efficiently, in which FIFO and LRU algorithms are often used to replace objects. However, media streaming is different from Web objects and the P2P network is also different from the client/server model and has its own features so that the system performance may be restricted when these algorithms are applied in distributed environment. To solve this problem, FIFO and LRU are analyzed and then two algorithms are presented, evaluated and compared with FIFO, LRU and LSB （least sent bytes）. The SD algorithm makes its decision based on supply-demand relationship of media segments, and the REP algorithm ejects objects according to replicas count of segments respectively. By simulation, it is found that both algorithms performed better than FIFO and LRU in terms of initial buffer delay, movie replicas number and dependency on the root with various peers＇ arrival interval. In some scenarios, initial buffer delay of LSB is reduced by about 40 % compared with SD while the REP has an advantage over LSB in aspect of replicas number. It is proved that the system performance could be improved when SD and REP algorithms are exploited for cache replacement in streaming media service on P2P network.