【作者】 向伟；

【导师】 吴刚；

【作者基本信息】 中国科学技术大学 ， 控制理论与控制工程， 2008， 博士

【摘要】 随着多媒体技术、网络技术和计算机技术的不断发展,视频点播、网络直播、视频会议、可视电话等多媒体已经广泛应用,成为日常生活的一部分。中小规模视频服务系统经过多年发展,已趋于成熟,但在向大规模/超大规模视频服务系统的迁移过程中,系统规模的扩展、网络的异构性、用户需求的提升,对现有的视频服务器体系结构、存储、传输和服务策略等提出了巨大挑战。可扩展的视频服务器体系结构和高效的带宽复用策略是扩展视频系统服务规模的两个主要手段,已成为超大规模视频服务研究的热点。本文围绕这两个问题,研究了异构网络环境下流媒体服务模式。本文在国家高技术研究发展计划(863计划)“十五”重大专项“高性能宽带信息网(3TNet)”、国家广电总局“海南省IPTV示范网络的建设”和“海南双向HFC实验网络”等课题的基础上,围绕异构网络环境下的流媒体服务模式展开研究,结合3Tnet、有线电视网和互联网的特性,研究了流媒体服务架构、传输模式、带宽复用等关键性问题,提出了一些新的思想和方法,并设计了相应的算法。主要研究内容和创新点如下:流媒体服务需要消耗大量的计算和存储资源,单台服务器的服务能力有限,在提供大规模并发服务时通常需要建造服务器集群。本文针对3TNet中主干网——ASON数据链路的传输特性,在多级缓存的视频点播服务系统基础上,提出并实现了支持异地存储影片VCR(Video Cassette Recorder,录像机)功能的视频点播服务策略。该策略利用3TNet数据高速传输的特点,采用异地服务的模式,降低边缘媒体服务器的存储压力,同时不因媒体内容的异地存储导致额外的启动延迟。本系统在上海长宁区IPTV(Internet Protocol Television,网络电视)示范运营工程的实际运营表明,该策略可以有效地缓解中心服务器的压力,适合大规模IPTV商业运营。单播采用独占模式提供服务,系统规模受到很大限制,组播是一种有效的解决途径。本文针对有线电视网,分析了HFC(Hybrid Fiber Coaxial,光纤同轴电缆混合网)双向网络特性,设计了一套适合该网络的流媒体服务平台。在该平台基础上针对HFC网络广播的特性,提出了分段补丁算法,以分段补丁的形式向用户提供数据,代替传统补丁算法提供完整补丁流的形式。在算法中,利用HFC网络的广播特性,用户同时从多个信道接收视频数据,无需消耗附加的网络资源。理论分析和仿真试验表明该算法在有限的带宽条件下,最大限度为用户提供视频点播服务,同时支持用户的VCR操作。对于互联网而言,由于技术条件的限制,目前网络层组播还无法广泛应用。随着个人计算机技术的飞速发展,客户端的存储、计算能力有了很大提高,可以作为流媒体服务系统中的一个节点提供服务。在此背景下,应用层组播被认为是解决服务扩展性的最佳途径。本文针对下一代互联网络的特性,提出了基于P2P的时移电视传输策略,将补丁技术与P2P技术相结合,有效地节省了视频服务器及主干网络的资源,同时对服务规模没有限制。在此基础上引入网格技术,提出时移电视服务系统(Time-shifred TV on demand based on grid,GridTVOD),将视频服务器和服务节点组织为流媒体服务网格,视频数据传输采用P2P和Patching相结合,用户作为网格节点,在享受服务时,也作为服务端为其它节点提供服务。理论分析和仿真试验表明系统具有良好的可扩展性、可组织性、安全性。更多还原

【Abstract】 With the ripid development of multimedia technology, network technology and computer technology, video-on-demand, network broadcast, video conferencing, video telephony and other multimedia applications have become part of everyday life. After years of development, small or medium scale video service system is becoming more mature. However, there are some great challenges on the way towards the large or ultra-large scale video service system, including challenges to the existing existing video server architecture, service strategy, storage and transmission technique, caused by the expansion of system size, the heterogeneous network, the user needs upgrading. Current research of the ultra-large scale video service system are focused on scalable video server architecture and efficient bandwidth sharing strategy, which are two major means of expanding the video service systems. Service models for streaming media in heterogeneous networks presented in this dissertation are developed to solve the two problems, which has an important theoretical value and practical significance.The work in this dissertation is based on "China High Performance Broadband Information Network (named 3TNet)" project, "Hainan IPTV demonstration network building" and "Hainan bidirection HFC experimental network" projects. This dissertation discusses service models for streaming media in heterogeneous networks, including service structure, service model, and bandwidth multiplexing. The main research contents and contributions are summarized as follows:The capacity of a single server is quite limited, clustered servers are needed to provide large scale streaming media services. Based on transmission characteristics and the hierarchical caching architecture of 3Tnet, the dissertation proposed and implemented a VOD service scheme to support remote storage video VCR function. It makes full use of the high bandwidth and distributed storage policy of 3TNet, decreases the demand of the storage capacity of streaming media server. The result of business management proves that the proposed scheme can greatly reduce the load on the center server and provide null startup latency for clients.In unicast VOD systems, the server has to reserve a dedicated video channel for each user for the entire duration of the video session. Consequently, the required server and network bandwidth resources increase linearly with the number of concurrent users to support. Multicast is an effective solution. Based on the project of CATV, the dissertation analyzed the characteristics of HFC network, and designed a streaming media service platform for the network. Based on the broadcast characteristics of HFC, the dissertation proposes a novel delivery scheme, named as piecewise patching (PP). The piecewise patching scheme provides the video data for the users in a piecewise mode instead of a whole patching stream which includes all missing data. Simulation results show that the scheme improves the performance of Time-shift TV service significantly in terms of total server bandwidth requirement.For the Internet, multicast can be used widely because of the limiting technical condition. At present, the storage, computing power of client has been greatly improved. Clients as streaming media service node become a reality; application layer multicast is a new way to solve expansion of services. The dissertation proposed a new transmission scheme applied on the Time-shifted TV. On the basis of Patching, P2P was introduced to reduce the bandwidth of the Video Server and the bone network. The scheme can significantly reduce the pressure of the Video Server. Based on the scheme, the dissertation designed a new Service Architecture named by Time-shifted TV on demand based on grid (GridTVOD). In GridTVOD, media servers and service nodes composed a streaming media service grid, which was designed on the base of Globus MDS. The GridTVOD used a peer-to-peer approach to cooperatively stream video using patching techniques, in which each peer can serve as both a client and a mini-video server.更多还原