A Review of Multipath Routing Protocols: From Wireless Ad Hoc to Mesh Networks

Multipath routing allows building and use of multiple paths for routing between a source-destination pair. It exploits the resource redundancy and diversity in the underlying network to provide benefits such as fault tolerance, load balancing, bandwidth aggregation, and improvement in QoS metrics such as delay. There are three elements to a multipath routing, namely, path discovery, traffic distribution, and path maintenance. Path discovery involves finding available paths using pre-defined criteria. A popular metric is path disjointness, a measure of resource diversity between paths. Traffic distribution strategy defines how concurrently available paths are used, and how data to the same destination is split and distributed over multiple paths. Path maintenance specifies when and how new paths are acquired if the states of currently available paths change. There are numerous multipath routing protocols proposed for wireless ad hoc networks, exploring characteristics in mobility, interference, topology, etc. We present a selection of these protocols and give a discussion on how multipath techniques can be extended to wireless mesh networks. Lastly we briefly describe the path selection framework in the current proposal for IEEE 802.11s mesh standard. Although the proposal does not define use of multipath routing, its extensible framework for path selection provides provision for such protocols to be implemented. 1