A distributed adaptive cache update algorithm for the dynamic source routing protocol

On-demand routing protocols use route caches to make routing decisions. Due to mobility, cached routes easily become stale. To address the cache staleness issue, prior work in DSR used heuristics with ad hoc parameters to predict the lifetime of a link or a route. However, heuristics cannot accurately predict timeouts because topology changes are unpredictable. In this paper, we propose to proactively disseminate the broken link information to the nodes that have that link in their caches. We define a new cache structure called a cache table and present a distributed cache update algorithm. Each node maintains in its cache table the information necessary for cache updates. When a link failure is detected, the algorithm notifies all reachable nodes that have cached the link in a distributed manner. The algorithm does not use any ad hoc parameters, thus making route caches fully adaptive to topology changes. We show that the algorithm outperforms DSR with path caches and with Link-MaxLife, an adaptive timeout mechanism for link caches. We conclude that proactive cache updating is the key to the adaptation of on-demand routing protocols to mobility.