Predictive Caching Strategy for On-Demand Routing Protocols in Wireless Ad Hoc Networks

Route caching strategy is important in on-demand routing protocols in wireless ad hoc networks. While high routing overhead usually has a significant performance impact in low bandwidth wireless networks, a good route caching strategy can reduce routing overheads by making use of the available route information more efficiently. In this paper, we first study the effects of two cache schemes, link cache and path cache, on the performance of on-demand routing protocols through simulations based on the Dynamic Source Routing (DSR) protocol. Since the path cache DSR has been extensively studied, we focus in this paper on the link cache DSR in combination with timer-based stale link expiry mechanisms. The effects of different link lifetime values on the performance of routing protocol in terms of routing overhead, packet delivery ratio and packet latency are investigated. A caching strategy incorporating adaptive link timeout is then proposed, which aims at tracking the optimal link lifetime under various node mobility levels by adaptively adjusting the link lifetime based on the real link lifetime statistics. The performance of the proposed strategy is then compared with the conventional path cache DSR. The results show that without a timeout mechanism, a link cache scheme may suffer severe performance degradation due to the use of broken routes, while the proposed adaptive link cache strategy achieves significantly improved performance by reducing the routing overhead when the network traffic load is high.