Preemptive Multicast Routing in Mobile Ad-hoc Networks

Preemptive route maintenance allows a routing algorithm to maintain connectivity by preemptively switching to a path of higher quality when the quality of the currently used path is deemed questionable. Preemptive routing initiates recovery actions early by detecting that a link is likely to be broken soon and searching for a new path before the current path actually breaks. Preemptive route maintenance has been used for unicast (point-to-point) communications in wired networks and in mobile ad-hoc networks (MANETs) to minimize the number of route breaks and thus packet losses, and end-to-end delays. In addition to these advantages, we show that preemptive route maintenance can help minimize control overhead and improve the scalability of multicast routing protocols in MANETs. In this paper, we present design and implementation issues of preemptive routing for multicast in MANETs. We then describe a preemptive multicast routing protocol based on ODMRP (On-Demand Multicast Routing Protocol), which we call PMR (Preemptive Multicast Routing). PMR significantly improves the scalability of ODMRP: it offers similar or higher packet delivery ratios while incurring much less control overhead. Our simulation results have confirmed these advantages of PMR.