Software Implementations of VOD System in Community Broadband Network

随着智能化住宅小区的普及和宽带网络接入技术的发展，各种基于宽带技术的应用服务也日益被人们所熟悉，VOD视频点播是目前最关键的应用之一。在视频点播领域的关键是以合理经济的成本为尽可能多的用户提供交互点播服务。对如何提高VOD服务器性能以提高并发节目流的个数和同时服务的用户个数，我们进行了深入的研究。从技术角度，VOD系统可以分为两种基本类别：基于单播的v0D系统和基于组播的VOD系统。单播VOD系统能提供独立的用户交互功能，但是每个用户独占一个节目流资源，比组播共享方式的成本高。组播方式中，所有观看同一节目流的用户共享服务器资源，由智能的网络交换系统提供分发，用户只能象选择电视频道的方式更换节目，而没有象看录像机／光盘节目所具有的快进搜索方面的功能。这两种方式的优缺点是互补的。我们开发了同时提供这两种服务的视频点播系统。本文主要介绍我们设计开发的基于以太网的智能小区的VOD系统，包括基于组播技术和基于单播技术的两个子系统的设计与实现。全文共分七章。第一章介绍了VOD系统的背景知识，包括VOD系统的组成、分类、应用前景等。第二章从总体上介绍了我们实验室设计开发的智能小区宽带接入系统。该系统不仅包括VOD视频点播系统，还有其他如数字电视直播、视频会议、工P电话、网管计费等子系统以及提供支撑的家庭网关、交换机等设备。它们共存于这个大系统之中，互为支撑和补充。第三章介绍了视频节目的制作处理和存储。第四章深入研究影响服务器性能的重要因素。第五、六两章则分别介绍了基于组播和单播的两个子系统的具体实现。第七章是对目前工作的总结和进一步改进工作的展望。With the phenomenal prevalence of the intelligent communities and the rapid development of broadband access technologies, a variety of broadband technology based applications are becoming familiar to people day by day. Video on demand system is the typical case among those applications. The key challenge in VOD domain is to provide interactive services for thousands of potential users at a reasonable cost. In order to address this problem, we carried out a deep study on VOD server performance aiming at maximizing the total amount of concurrent data streams the system can bear as well as maximizing the user number the system can serve simultaneously. Depending on the technology adopted, VOD system can be distinguished into two categories. The first one is based on unicasting and the second one uses multicasting. They all have their own advantages and disadvantages. Unicasting based systems can offer the user full control over the media stream, thus are much preferable by the user. But since each stream is exclusive occupied by a single user, the cost per user is very high. Therefore the price of the service may hinder the wide acceptance of the system. On the contrary, in the multicasting systems, all the users ordering the same program can share the resources while the intelligent network switching system is on duty of the transmitting and dispatching of the program data. Hence the system can theoretically support unlimited number of users at one time. On the other hand, since each stream is shared by numerous users, it's difficult to provide sufficient interaction to make the users much satisfied. As a result, we can see that these two kinds of systems are complementary to each other. In order to get the widest market coverage, we decided to provide these two kinds of systems at one time. This thesis mainly introduces and illustrates the Ethernet based intelligent community VOD system designed and developed in our lab, including the design and implementation of two independent and complementary subsystems: the unicasting VOD subsystem and the multicasting VOD subsystem. It consists of seven chapters. In the first chapter, I simply analyze VOD system in detail covering the constitution, the categorization, and the prospect. The second chapter introduces the intelligent community broadband access system as a whole. This system is designed and developed by our lab. It not only includes the VOD subsystem, but also encompasses several other subsystems: live digital TV program, video conference, IP phone, network management, accounting, etc. There is still some other supporting equipment: switches, residential gateways and so on. They coexist in the big system, supporting and supplementing each other. The third chapter described the processing and storage of the video program data. In the forth chapter, I give a deep and broad analysis about the critical elements which affect the performance of a VOD server greatly. Chapter five and six elaborate the concrete implementation of these two systems respectively. The last chapter is a general statement of the system and future work