The effects of cache organizations on the performance of on-demand routing protocols in ad hoc networks

Route caching strategy is important in an on-demand routing protocol in wireless mobile ad hoc networks. While high routing overhead usually has a significant performance impact in low bandwidth wireless network, a good route caching strategy can reduce routing overhead by making use of the available route information more efficiently. In this paper, we stud), the effects of two cache organizations, "link cache" and "path cache", on the performance of on-demand routing protocols through simulation. The effect of a static link timeout mechanism is studied and an adaptive link timeout mechanism is proposed. The adaptive timeout mechanism aims to keep tracking of the "optimal" link lifetime under varied node mobility levels by dynamically adapting the estimated link lifetime using a moving average from the real link lifetime statistics. We present the simulation results in terms of routing overhead, packet delivery ratio, and end-to-end delay. The results indicate that without an appropriate stale link removal mechanism, a link cache organization may suffer severe performance degradation because of the large number of route error messages generated. However, with an appropriate timeout mechanism, the link cache organization reduces the routing overhead significantly and outperforms the path cache when the network traffic load is high. Our simulation is based on the Dynamic Source Routing (DSR) protocol.