基于树型代理透明服务模型的流媒体复本放置

Replica Placement for Streaming Media System Based on Tree-Proxies Transparent Service Model

针对树型网络的路由机制和流媒体数据访问的分布特点,建立了树型代理透明服务模型,提出该模型上的流媒体复本放置问题.分析了常用的前缀放置算法在树型代理模型上的局限性,提出了非定长、可非连续的放置策略,并给出两种贪婪式的复本放置算法:自底向上逐层放置的层次型贪婪式复本放置算法(HGPA)和在全树范围逐块贪婪放置的全局贪婪式放置算法(GGPA).仿真实验结果表明:HGPA和GGPA算法均能有效降低服务器负荷,减少网络访问成本,性能均优于前缀放置算法;GGPA算法性能略优于HGPA算法,但时间代价过高;综合来看,HGPA是树型代理上较理想的放置方案.

According to the routing mechanism in tree networks and the distribution characteristics of streaming media accesses, this paper proposes a tree-proxies transparent service model and discusses the problem of the replica placement for streaming media system based on the model. Then, by analyzing the limitation of the commonly-used prefix placement algorithm on tree-proxies model, a non-fixed-length discontinuous placement strategy and two greedy algorithms, namely HGPA （Hierarchical Greedy Placement Algorithm） and GGPA （Global Greedy Place- ment Algorithm） , are put forward. HGPA places replica level by level from the bottom up in tree proxies, while GGPA performs a greedy placement per segment in the whole tree. Simulation results show that （ 1 ） both HGPA and GGPA effectively reduce the server load and the cost of network access and are of better performance than the prefix placement algorithm; （2） GGPA has a slightly better performance but costs more time than HGPA; and （3） comprehensively speaking, HGPA is an ideal replication solution for tree proxies.