Research Of Multicast Protocol For Ad Hoc Network

Ad Hoc network has been widely used in military communications, simultaneous conversation, and disaster reconstruction etc. The technical features of non-central, self-organizing and mobile nodes make it have absolute advantages of quickly building up a temporary network, high survivability system, unnecessary network infrastructure and high efficient transmission. In recent years,the development of multicast technology has overcome the defects of small network bandwidth, limited host resource and low network utilization, it plays a key role in Ad Hoc network applications such as real-time messaging, video conference and remote interaction.At present, multicast routing protocol of Ad Hoc network can be divided into three categories, based on the tree, based on the net and hybrid type of multicast routing protocol. The paper studies several typical multicast routing protocols, analyzes the MAODV(Multicast Ad Hoc On-Demand Distance Vector) and ODMRP(On-Demand Multicast Routing Protocol)protocols, then it simulates by using QualNet network simulation software, analyzes their performance when the number of multicast data receiving nodes, the speed of nodes and the number of multicast data sending nodes are changed. The result shows that the overall performance of ODMRP protocol is superior to MAODV protocol and more suitable for Ad Hoc network features of multi-hops and topology changing frequently.Based on analyzing the routing mechanism of the ODMRP protocol in detail, the ODMRP-TE (ODMRP with Time Estimate) protocol with time estimating mechanism is proposed against the shortcomings of the ODMRP protocol. The main improvements lie in.First, a table is added to maintain time information and the packet of JOIN-REPLY which is used to respond to routing requests is improved. The nodes will predict time that sends data packet from one node to another according to the record in timetable. Second, according to the time of sending data and the routing update interval , the nodes send a packet of delay routing requests to inform the multicast sending node to adjust the routing update interval that will reduce the overheads of network and improve the efficiency of data transmission.The simulation experiment shows that the ODMRP-TE protocol is effective.Finally, in summary, the paper analyzes the problems in the process of research work and presents the prospect in the future research.