Design And Implementation Of An Application-layer Multicast System

With the increasingly widespread of Internet multimedia applications such as video-on-demand(VOD) and video conferencing, the traditional unicast can no longer suit the transmission characteristics of this type of business ,so multicast technology has become a hotpot. Multicast can solve the transmission problem of redundant data, and can effectively save network resources. However, because of the restrictions on the deployment of IP Multicast and the flaws of protocol itself , multicast has not been widely deployed. Then the application-layer multicast (ALM) appears, in which the Multicast functions are transferred from multicast router to the end system. It builds multicast network directly on the end system, and don't need special support from the network equipment. It appeared to solve the inherent problems of IP Multicast, especially the restrictions that the deployment of IP Multicast needs the support of routers.Various application-layer multicast systems and protocol are studied in this paper. On this basis, a new application-layer multicast protocol based on tree first is proposed. It is mainly for the medium-scale real-time applications, using a distributed architecture, separating the control panel from the data transmission panel, designing cache mechanism for nodes to join / leave the multicast group effectively, and ensuring the stability of the multicast tree, enabling the nodes to provide services according to their ability by detecting the network state between them. And the NAT traversal mechanism is designed for point-to-point communications in this paper. The prototype system is designed and implemented based on the new protocol, the system assumes distributed architecture, runs the new application-layer multicast protocol, and uses JMF technology in the transmission of the video stream.Finally, the functional and performance of this prototype system is tested and analyzed. The test results show the design of protocol is correct, the system modules can work correctly, each node can receives fluent video stream, the functionality and the performance can achieve the initial design target.