QoS-constrained Fault-tolerant Routing in MANETs based on Segment-Backup Paths

In the context of mobile ad hoc networks (MANETs), we consider the problem of identifying (a) an optimal primary path which satisfies the required QoS constraints, and (b) a set of alternate paths that may be used in case a link or a node on the primary path fails. The alternate paths are also required to satisfy the same set of QoS constraints as is the case with the primary path. This methodology ensures two things: (a) when there is no link or node failure the traffic moves along the preferred optimal route, but (b) if there is link or node failure the traffic will be instantly re-routed along a route that continues to satisfy the same QoS constraints, although it may experience some performance degradation. In the paper, we have proposed that the traffic be re-routed along a sub-path that by-passes a segment of the primary path that contains the failed link or node. The identification of the segments is not fixed a priori but is determined based on (a) availability of alternate paths, and (b) so that QoS constraints are met. This approach ensures that if connectivity between a given pair of nodes is rich enough then for any primary path one can always find alternate paths so as to address the problem of link or node failure. This flexibility in identifying the segments can also be used to ensure that the delay in switching traffic over to an alternate path, and the resulting packet loss, are bounded. We have described a protocol to identify (a) a primary path, (b) the collections of segments, and (c) the corresponding set of alternate paths, one for each segment, each of which satisfies specified QoS constraints, and so that the delay in switching traffic over to an alternate path is bounded