The Study Of Video On Demand System Based On HFC

VOD is key service of Interactive TV, the ability of selecting program for viewing freely and controlling playback fully gets rid of the restriction of watching traditional TV passively. The IP-QAM technology uses rest bandwidth after DTV's transformation to transmit the program stream, which has the advantage of high transmission quality. It is considered as the most appropriate technology of Interactive TV. However, in order to achieve return of user's on-demand and playback control information, it is necessary to build additional IP network as the IP-QAM VOD's return channel, the user do not demand the program until he takes advantage of new two-way STB with DVB-C and IP interface. These result in some problems such as high cost of Interactive TV's construction and maintenance, low coverage, without supporting the deployed one-way STB, and so on.Because return information of IP-QAM VOD is the small amount of data and delaying requirements are not high, the method using mobile communication network as a return channel for the new IP-QAM VOD system is proposed. It is able to carry data communications of on-demand and interactive playback control information. So the whole flow is carried out that the front server is accessed by the mobiles, the program is retrieved, the request of on-demand and playback controlling is submitted, the on-demand program stream is sent to the IP-QAM device in the HFC networks and the IP-QAM broadcast the program stream. This solution does no longer need specific return IP networks. Making use of full coverage of the mobile communication network can achieve the realization of all users'on-demand. It has advantages of easy deployment and low cost of construction and operation. Especially the early one-way STB of deployment possesses a video-on-demand function.Then test system based on the mobile communication networks as return channel for IP-QAM VOD is developed. On the IP-QAM, the mobile communication portal server and SRM server are designed and implemented, and the VOD server based on LIVE555 Media Server is developed. The mobile communication portal uses WAP technology to support the mobile generally, provides the function of inquire, receives the on-demand request and playback control on WAP, and transmits the request to SRM.SRM determines the destination's IP-QAM according to the mobile number, and adopts RTSP to control VOD server to send stream. The difference from traditional IP-QAM VOD's sending program stream directly is that VOD server first sends the tip stream to prompt the viewer to see the notice information on TV and confirm the on-demand by the mobile. SRM does not instruct VOD server to send true stream to ensure that the user view it fully until confirmation is received. On the foundation for system implementation, the communication protocol between Portal and SRM is defined, and RTSP protocol between the SRM and the VOD server is extended.Using mobile communication network as a return channel solves the bottleneck of user access, facing up a challenge of the performance of a server becomes a limited condition of plenty of users'concurrency. In order to achieve the low-cost solution, VOD server clusters based on standard servers are built. Load balancing and redundancy programs allocation algorithm are designed so that all transactions are scattered on the member video server, and a server fails, its carried transactions can evenly move to other servers. For hit shows, using the way that a copy of the dynamic establishment on the multiple servers realizes a large number of concurrent on-demand.