关键词: 按需广播, 点对点, 网络拓扑结构, PRLS算法

Abstract: Peer-to-peer file-sharing in HFC network is short of bandwidth resource.In order to raise band utilization rate，a hybrid network topology which integrates data broadcasting system and P2P systems is proposed by taking use of the free broadcasting channels to send the indexes of file resources.At the same time，the authors research of the classic pull-based data broadcasting algorithms under this network topology and design a pull-based algorithm-PRLS（Preemptive Request-Length-Serial），to improve the efficiency of broadcast scheduling.In the last part of this article comparisons are made between this algorithm and the former classical pull-based algorithms.Simulation experiments show that the performance of the algorithm is obviously better than them on users’ average waiting time and the balance of broadcasted length between hot and cold file indexes，which verifies the effectiveness of the PRLS algorithm.

Key words: pull-based broadcast, peer-to-peer, network topology, Preemptive Request-Length-Serial（PRLS）