Improving Route-Freshness

Ad-hoc routing protocols in mobile environments face a fundamental tradeoff between delay and communication overhead. Since routes become stale as nodes move, nodes need to frequently recompute routes, leading to an increase in control traffic overhead. In dealing with this tradeoff, protocols often adopt a fixed stance: some protocols assume frequent node movement, regularly recompute routes and incur large bandwidth overheads while others assume a stable environment, recompute routes only when existing routes fail, and suffer large delays when nodes move. In this work we demonstrate how reactive protocols can improve the freshness of their routes while maintaining control bandwidth by dynamically estimating route-staleness. We show that nodes can use a technique called Strong Detection to analyze their routes for inconsistencies that reveal staleness. We then provide algorithms to selectively refresh routes until the inconsistencies that reveal staleness disappear. We apply this Strong Detection technique to the AODV and DSR protocol and experimentally demonstrate that the freshness of AODV routes can be improved by approximately 30%. For the DSR protocol we show that the validity of routes can be improved by around 5% and delays due to unnecessarily long routes reduced from between 10% to 15% without incurring additional control overhead.