Exploring Long Lifetime Routing in Ad Hoc Networks
In mobile ad hoc networks, node mobility causes links between nodes to break frequently, thus terminating the lifetime of the routes containing those links. An alternative route has to be discovered once a link is detected as broken, incurring extra route discovery overhead and packet latency. A simple solution to reduce the frequency of this costly discovery procedure is to choose a long lifetime route carefully during the route discovery phase rather than a simple random shortest-path route scheme. This simple solution, although straightforward, requires investigation of several questions before it can be implemented. Specifically, how much effect does node mobility have on the link lifetime? Correspondingly, how much effect does it have on the route lifetime? How much lifetime extension can we achieve by using a long lifetime route compared to a randomly chosen shortest-path route? How much benefit can we obtain by using these longer lifetime routes, and what is the tradeoff of using them? Only after we have answered these questions, may we gain enough insight to determine under what circumstances long lifetime routes are worth being discovered and implemented. We have formulated the distribution of a link lifetime and correspondingly the distribution of a route lifetime through theoretical analysis. We have also proposed an algorithm to determine the longest lifetime routes at different route lengths, and we have experimentally compared these long lifetime routes with traditional random shortest-path routes, revealiong the tradeoff of using long lifetime routes of different lengths.
We experimented on DSR using the long lifetime routes and random shortest path routes. The performance of TCP over these two types of routes is as follows.
Through this experiment, we conclude that LLR is good for several scenarios. The first application to use LLR is to find an LLR with the shortest route length, or we may find one-hop longer LLR with an even longer route lifetime. LLR is also suitable for applications that require a long session but have very low traffic. Telnet is an example of this type of application. LLR also provides a stable route that is very crucial for QoS-based applications. LLRs may serve as backup for common SPRs for both stability and efficiency.
Based on these results, we have proposed a long lifetime route discovery scheme using link lifetime estimation. This route discovery scheme provides two long lifetime routes with the shortest route length through one discovery procedure. Simulation results show that with accurate lifetime estimation, this approach performs close to a global Long-Lifetime Route (LLR) discovery algorithm, and is therefore able to substantially improve the performance of on-demand routing protocols such as DSR.For more information about this project, contact Zhao Cheng.