Research Of Application-Layer Multicast Based On IPTV Carrying Network

IPTV(network television)provides many real-time, non-real-time multimedia services for users by using IP networks. It is an interactive television network business, and it uses the bi-directional IP network which has existed to provide live television, on-demand programming, time-shifted TV. Judging from the current test operation of the IPTV business situation,it still has a few gaps comparing with the cable television, for examples, image clarity, mouth shape and voice synchronization, channel switching time, the number of channels. There are many technical problems to be solved:①video encoding,②storage,③data transmission,④multi-media terminal,⑤technical standards. Because the bandwidth of network is limited, the transmission technology on carrying network must be improved to improve the TV picture quality.So that it is avoided to transmit the same content by unicast way. So near the different terminal users transmit the data only in a trunk-line when receiving the television information. But data is replicatied and distributed in another branch of the router, that is, Multicast.Multicast is of high-performance which sent the data packet to the more receivers on the network at the same time. And it supports point-to-multipoint communications and multipoint-to-multipoint communication. Multicast technology avoids a multi-unicast stream for each recipient to establish communication links and to send a separate packet. It is a key technology of IPTV to improve the utilization of the network. There are two types of main multicasts: network layer multicast services and application layer multicast. Network layer multicast is IP multicast, which has advantages of the bandwidth-efficient and simple equipment. However, because of technology and management, IP Multicast is difficult to popularize in the short term through Internet environment. ALM will move multicast from the network layer to application layer. An IP Multicast close to the efficient use of bandwidth is made with not changing the Internet architecture. So ALM has become multicast technology one of the hot spots.Requirements of multicast technique, such as group size, dynamic, member's computing ability, and network interface, vary from many applications. IPTV send television signals of operators to multiple recipients through the Internet, and users receive messages by set-top boxes, computers, hand-held mobile electronic devices. The user grpups of IPTV have such characteristics as great group size, disperse of users, time centrality of member's joining and leaving group, and real-time content. At present, IPTV has been popular, but doesn't completely solve the core problem. In this paper, the multicast protocol NICE is improved by analysizing requirements of multicast technique on IPTV.The main works of the paper are as follows:①The features and the applications of IPTV technology are analyzed. And the technical bottle-necks and solutions of IPTV are studied;②The status and development of IPTV carrying networks are presented;③The principles of Multicast and the features of IP Multicast are introduced, and its characteristics and application prospects are analyzed;④The ALM is studied deeply, and the advantages and disadvantages of various ALM's are analyzed;⑤The protocol NICE of widely-used ALM are studied deeply and are improved.And E_NICE which services for IPTV in carrying network is proposed. The effectiveness of improved E_NICE is verified through the simulation experiments.