统综述基于P2P的视频点播系统综述.doc

摘 要 近十年来，基于对等网络（Peer-to-Peer，P2P）的视频点播系统（Video-on-Demand，VoD）受到了越来越多的关注。它吸引人的原因在于，与传统的基于服务器/客户机结构的视频点播系统相比，P2P技术具有成本低、扩展性好的优点。但是，由于对等网络内在的不稳定性、异构性，这类系统在实现上面临着诸多挑战。本文对现有的该类系统的体系结构进行模块划分，并对各模块的实现策略进行讨论；特别是对VoD/P2P实现中的三个主要方面，即数据传输、数据存储、激励机制进行了综述。 关键词 对等网络；视频点播；传输拓扑；编码方案 中图法分类号 TP393 P2P-based Video-on-Demand Systems: A Survey SHEN Shi-Jun LI San-Li (Tsinghua National Laboratory for Information Science Technology, Beijing 100084) (Department of Computer Science and Technology, Tsinghua University, Beijing 100084) Abstract Over the past decade, Peer-to-Peer (P2P) based Video-on-Demand (VoD) systems have received a tremendous amount of research focus. They are immensely attractive because of their cheap deployment and high scalability compared to traditional Client/Server (C/S) based VoD systems. However, due to the instability and heterogeneity of P2P networks, there are many challenges in designing, implementing, and deploying such systems. For instance, the lack of resources (e.g., source nodes, bandwidth, storage, etc.) usually becomes a barrier that prevents practical systems from normal operation. Based on the observation, this paper outlines the components of existing VoD/P2P architectures and surveys approaches to their design, focusing on how to make full use of limited resources in P2P based VoD systems. Specifically, the authors present a survey in three aspects: (1) data transmission, referring to how to make full use of nodes’ bandwidth; (2) data storage, referring to how to make full use of nodes’ storage; and (3) incentive mechanisms that stimulate nodes to contribute more resources. Keywords Peer-to-Peer; Video-on-Demand; transmission topology; encoding scheme1 引言 VoD/P2P的传输希望解决如下的问题：如何从一个或多个源节点向多个目标节点分发数据，使之在动态的、异构的网络中：（1）保证视频的传输率，即目标节点的有效输入带宽不能小于视频的码率；（2）减少用户等待时间，即用户从发出点播请求到视频播放的时间间隔尽可能短；（3）降低带宽浪费，即点播不能消耗很多不必要的带宽而影响其它应用。近年来，对传输问题的研究主要集中在拓扑结构与编码技术两方面。 2.1 传输中的拓扑结构 N），并将这r数据块作“异或”操作以生成冗余块。为了使任取N（或稍大于N）冗余块即可解码，实际的编码过程更复杂一些。相关的编码实例包括Tornad