Research And Improvement Of DSR Routing Protocol For Ad Hoc Networks

Ad Hoc networks don't use any fixed infrastructure. Because of its mobile, non-infrastructure nature, developing support for routing is one of the most significant challenges in ad hoc networks and is critical for the basic network operation. Routing protocols developed for wired networks are inadequate here as they not only assume mostly fixed topology but also have high overheads. This has lead to several routing proposals specifically targeted for ad hoc networks. In the recent past, this problem was addressed by many research efforts. Various approaches are proposed in a large body of literature.As one of the prominent on-demand protocols, DSR (Dynamic Source Routing) has some generic optimizations. DSR makes aggressive use of source routing and route caching. With source routing, complete path information is available and routing loops can be easily detected and eliminated. Nodes are allowed to overhear on-going data transmissions nearby to learn routes and catch them free of cost. To take full advantage of route catching, DSR replies to all requests reaching a destination from a single request cycle. Thus the source learns many alternate routes to the destination, which will be helpful in the case the primary route fails. However, basic DSR protocol lacks effective mechanisms to purge stale routes in the route catching. Use of stale routes not only wastes precious network bandwidth for packets that are eventually dropped, but also causes cache pollution at other nodes when they forward/overhear stale routes. So keeping the routes in the cache active is very important.When the source node is actually sending packets to the destination node using a source route the route maintenance works. If the sender of a link along the source route doesn't receiver acknowledgement from its next hop, the sender treats the link as currently "broken". It will remove this link from its Route Cache and will return a "Route Error" to each node that has sent a packet routed over that link since an acknowledgement was last received. Obviously it is too long for the source node to detect the route is broken as it's the sum time of the data sends and the "route error" feedbacks.In order to improve caching strategies the paper introduces the local connectivity mechanism in AODV protocol into the basic DSR protocol. The nodes exchange hello messages with each other and they may determine connectivity by listening for packets from their set of neighbors and check if the routes in their catches are active. What's more, the modified DSR has the local repair mechanism with the small world theory to find the replace route nearby when the route is detected to be failure. The proposed scheme tries to reduce the cost of route reconstruction. The simulation shows that the performance of the new approach, DSR-ALDS, is improved in the aspects of end-to-end delay, packet delivery fraction and routing load.