A Study Of Application-level Multicast Technology In Overlay Network

With the development of computer network, the emergence of many new multimedia group applications, such as video conferencing, video-on-demand and distance learning, require multicast communication service imminently. Compared with IP multicast, the greatest advantage of overlay multicast based on the concept of overlay network is that end systems perform all multicast communication functionalities instead of IP routers and it needn't change the lower network infrastructure, and can be deployed easily. Overlay multicast embodies the trend that the emphasis of network service research is shifting from network layer to application layer in the next generation Internet. Based on the study of the overlay multicast routing protocols and algorithms, the primary work and innovative ideas are as follows:Based on the study of basic theories and system frame of the overly network , this thesis has put forward an application-level multicast model for large overlay network system, named DHCM (density-based hierarchical clustering multicast) which has improved the IHC (Incremental Hierarchical Clustering) algorithm. This density tree of DHCM has the homogeneity and monotonicity properties, and divided the hosts into many hierarchies according to their density, and constructed a density tree to realize the shortest routing. At the same time, DHCM uses a p2p scheme in data transmission which transmits the data in zigzag fashion, but the traditional manner is that child node will get the data from the father node. This scheme will avoid the bottleneck for one node must transmit too many child nodes, and improve the data transmission efficiency of system. The experiment results compare with other application-level multicast have proved that DHCM can transmit the video stream efficiently and robustly.This thesis has proposed two problem model MRDL (Minimum radius, degree-limited spanning tree problem) model and LRRB(Limited radius, residual fraction-balanced spanning tree problem) model in order to resolve the problem "degree-limited and minimum delay spanning tree". At the same time, this thesis has given the corresponding heuristic algorithm: MRDL-H algorithm and LRRB-H algorithm. This paper have proposed some swap and switch operation to dynamically maintenant the multicast tree and introduced the Knock-down technology to make the tree has more expansibility. The simulation experiment result has prove that these two algorithms for different sizes of the multicast tree have a better adaptability and show the obvious advantage in the aspect of repeatedly using bandwidth and network resource using capacity, so these work prove the efficiency of these algorithms.In order to improve the network heterogeneity and the real-time transmission, this thesis has proposed a proxy-based overlay multicast system called iPALM (Proxy based Application-level Multicast). Its basic idea is that system uses efficiently data transmission of IP multicast in LAN, and every IP multicast area will has been set one proxy server named MPN, the backbone network will transmit data using application-level multicast, in this way the transmission of many nodes in the Internet can be realized. At the same time, iPALM has adopted the service subscribing mechanism in XML format, and use two level congestion control technology based on client and proxy server. This thesis also has described the function module picture, the protocol package's type and function and format definition, the detailed definition of table cashed in every module. The simulation experiment has proved that iPALM system can satisfied every different application request and save many network resource, which can offer network throughout and smooth the jitter in network transmission and improve the media service quality.