Research On Stability Enhancement Of Application Layer Multicast Model Based On Dual-Path Multicast Tree

Application layer multicast (ALM) which uses end hosts to implement the multicast function such as data forwarding has a prosperous prospect in the field of distributed multimedia communications. Compared with IP multicast, ALM is more simplicity, flexible and easy deployment. But the end host of ALM can freely quit multicast group, which leads to the interruption of multicast connection and result in stability problem of ALM. The stability problem of ALM limits its application. Therefore, it is necessary to improve the quality of ALM service by enhancing the stability.Firstly, in order to reduce the restoration time, to enhance the multicast stability and to improve the application layer multicast performance, a dual-path multicast tree solution is proposed which transports and forwards different data via two multicast trees, thereby other nodes can still receive the acceptable multimedia data and recover the multicast data according multiple description coding (MDC) without rebuilding the multicast tree through the other multicast tree of the dual-path multicast in case that some nodes join or quit multicast group. Computer simulation proves that this solution reduces the failure recovery time and has more merits and better performance than traditional scheme when node joins and exits the multicast.Secondly, in order to further reduce the multicast tree interruption, to enhance the multicast stability and to improve the application layer multicast performance, defines node stability degree based on node degree and node online time and proposes an algorithm of dual-path application layer multicast tree based on node stability degree. During the construction of the second dual-path multicast tree, the leaf nodes with higher stability will be closer from the source node, and the node location in multicast tree is dynamically adjusted according to the change of node stability. It is proved by computer simulations that this algorithm enhances the multicast stability and improves multicast performance compared with the basic dual-path scheme, and therefore it is suitable for multimedia multicast transmission.Furthermore, from the point of improving the transmission efficiency and the quality of service (QoS) of the ALM, the physical topology of underlying network is considered to avoid the rise of Propagation Delay which causes by the host node selecting the far node in the actual network when transmit the multicast data. The distance between the node and the source node and the distance between the node and its father node is measured by topology-aware and Round Trip Time (RTT). The algorithm of the second dual-path multicast of ALM based on the node stability is improved through the two distance. An algorithm of Dual-path ALM comprehensive based on the node stability and the node distance is proposed. The model of the dual-path multicast tree based on the node distance is build. Computer simulation proves that the Dual-path ALM based on the node distance reduce the influence on the transmission delay of the multicast tree compared with the Dual-path ALM based on the node stability degree, and the scheme of the distance between the node and the father node is better than the scheme of the distance between the node and the source node in the aspect of decreasing the Propagation Delay and improving the transmission efficiency and the QoS of ALM.Analyze the further work of the stability of the ALM and point out the unresolved problem on the basis of research result of this paper.