A Model of Topology Cache in Reactive Routing Protocols for MANETs

In a reactive routing protocol such as DSR, when a route search message is ‡ooded, a large number of nodes learn the path to the originator of the search. Moreover, each of these nodes learns paths to all upstream nodes along the route to the originator. Thus, during a route search, a large amount of topology information is distributed and stored in cache. This information is then used to reduce the number of hops future route search messages must travel. In this paper a model of the impact of topology cache is developed. The model allows the impact of cache to be estimated for a wide range of node speeds, node densities, network sizes, and values of cache timeout. When compared to simula- tion, the model predicts the number of hops that the route search message spreads within 10%. This model allows a wide range of analysis to be performed. For example, the paper includes an investigation of optimal cache timeout and an investigation of the impact of cache in highly mobile environments.