Research On The Method Of Multicast Congestion Control For Mobile Ad-Hoc Networks

Recently, with the development of the technology of the computer network and mobile communication, ad hoc network is developed sharply. The technology of multicast routing and its congestion control for ad hoc networks has received the concerns of more and more researchers. The paper gives a comprehensive survey and analysis of the existing multicast routing and its congestion control technique in ad hoc networks. According to the multicast routing characteristics of ad hoc networks, we present a novel algorithm for the grid-based multicast congestion control in ad hoc networks, which includes congestion detection, congestion feedback and traffic rate adjustment. The validity of algorithm is proved by simulation with NS2. The main aspects of work are described below:(1) The paper analyzes existing multicast protocols in ad hoc networks, and gives a comprehensive evaluation. By simulating some existing typical multicast routing protocols in the different conditions of ad hoc networks with NS2, we find that their performances degrade sharply under the higher load. The poor performances of these protocols stem from their attempts to inject packets into the network without performing any congestion control.(2) After studying the existing algorithms of multicast congestion control, we compare their advantages and shortages according to different criterions. We analyze the reasons that congestion control algorithms of the wired networks are not suitably applied to the ad hoc networks, and point out the deficiency in existing multicast congestion control algorithms of ad hoc networks.(3) A new method, called grid-based multicast congestion control for ad hoc network (GBAMCC), is presented and described in details. The main reasons of congestion are analyzed. By computing dropping packets ratios reflected degrees of congestion in mobile nodes, combining congestion degrees of current node with that of the downstream nodes, feeding them back to its upstream nodes, and adjusting upstream nodes traffic rate, the paper gives a whole multicast congestion control algorithm, which includes congestion detection, congestion feedback and traffic rate adjustment. The qualities of service in the transport of excessive data for ad hoc networks are improved.(4) The ODMRP based on the grid structure is chosen as the experiment platform tocheck the validity of GBAMCC. By employing C++ and Otcl to design algorithm for GBAMCC, and adding it into the routing agent of ODMRP, we give simulations of the algorithm in various scenarios with NS2. The results of the simulations show that ODMRP with congestion control obtains the better efficiency and fairness than that without congestion control.