Caching strategies in on-demand routing protocols for wireless ad hoc networks

An on-demand routing protocol for wireless ad hoc networks is one that searches for and attempts to discover a route to some destination node only when a sending node originates a data packet addressed to that node. In order to avoid the need for such a route discovery to be performed before each data packet is sent, such routing protocols must cache routes previously discovered. This paper presents an analysis of the effects of different design choices for this caching in on-demand routing protocols in wireless ad hoc networks, dividing the problem into choices of cache structure, cache capacity, and cache timeout. Our analysis is based on the Dynamic Source Routing protocol (DSR), which operates entirely on-demand. Using detailed simulations of wireless ad hoc networks of 50 mobile nodes, we studied a large number of different caching algorithms that utilize a range of design choices, and simulated each cache primarily over a set of 50 different movement scenarios drawn from 5 different types of mobility models. We also define a set of new mobility metrics that allow accurate characterization of the relative difficulty that a given movement scenario presents to an ad hoc network routing protocol, and we analyze each mobility metric's ability to predict the actual difficulty in terms of routing overhead experienced by the routing protocol across the scenarios in our study.