Multipath routing in wireless mesh networks

TLDR: It is argued that a routing protocol for ad hoc networks should fully exploit the rich connectivity of the network to improve the reliability of packet delivery and use several good paths to reach destinations, not just the one best path, without imposing excessive control overhead in maintaining such paths.

Abstract: Multipath Routing in Wireless Mesh Networks Marc Mosko ∗ Palo Alto Research Center 3333 Coyote Hill Road Palo Alto, CA 94304 Email: mmosko@parc.com Abstract— This paper addresses multipath routing in a mobile wireless network. We review the premise that a routing protocol should prefer disjoint path construction and argue that using disjoint paths limits route reliability in mobile ad hoc networks compared to using multiple loop-free paths that need not be disjoint. In a mobile ad hoc network, link lifetimes may be relatively short compared to traffic flows. The characteristics of a MANET are significantly different than the networks considered by Kleinrock in his original delay analysis of alternate path routing. In particular, on-demand routing protocols may suffer a significant delay during path discovery. We argue that a routing protocol should exploit the mesh connectivity over non-disjoint loop-free paths to improve s, t-connectedness lifetime in a mobile network. Exploiting mesh connectivity amortizes expensive path discovery operations and may lead to better performance than using disjoint or maximally disjoint paths. I. I NTRODUCTION The main objective of using multipath routing in a mobile ad hoc network is to use several good paths to reach destinations, not just the one best path [1], without imposing excessive control overhead in maintaining such paths. Multipath routing has long been recognized as an important feature in networks to adapt to load and increase reliability [2], [3]. Telecommunication networks adopted alternate path rout- ing, really a form of path failover, in 1984 [4]. Many routing papers on ad hoc routing suggest that the proposed routing protocol may operate correctly (i.e., provide multiple loop- free paths), without specifically addressing the performance of the protocol when multipaths 1 are used [5]–[9]. Other protocols suggest building alternate paths, but without claims of correct operation (e.g. [10]–[13]). Several papers measure route coupling [14]–[16], the mutual interference of routes in a common-channel multi-hop ad hoc network, and find routes with low coupling. Route coupling, however, makes every flow dependent on every other flow through an area and the papers on route coupling do not address the cost of maintaining low- coupled routes in an on-demand protocol; they typically use link-state pro-active protocols. Most of the works on ad hoc multipath restrict the number of potential routes to a small number, usually two. AOMDV [17] allows up to k link-disjoint RREPs, where one is the “quickest” path and the others are chosen from the next link-disjoint RREQs. SMR [18] builds two paths from the quickest RREQ and then collects RREQs 1 We use the term ”multipath” to denote a set of multiple paths to a destination that need not be node or edge disjoint. J.J. Garcia-Luna-Aceves ∗† Computer Engineering Department University of California at Santa Cruz Santa Cruz, CA 95064 Email: jj@soe.ucsc.edu for a period and chooses a second maximally disjoint path from the first. In a zone-disjoint scheme [16], only two paths are built, but they are not necessarily minimum. This scheme uses an iterative algorithm to discard the worst choice each round until only two paths are left. In this paper, we argue that a routing protocol for ad hoc networks should fully exploit the rich connectivity of the network to improve the reliability of packet delivery. In a nutshell, a well-designed multipath routing protocol should find many alternate loop-free paths to destinations and should keep those paths alive by sending some amount of data traffic over them as a function of their quality. Paths with poor quality or significantly longer distance should not be used. The exact methods used by a routing protocol to propagate metrics and distribute load between paths is an open ques- tion. Interestingly, a number of routing protocols for ad hoc networks that attempt to take advantage of multiple paths to destinations advocate the use of node- or edge-disjoint paths. Section II surveys the literature and makes the case that disjoint paths are not necessary to improve the reliability of wireless ad hoc networks. Furthermore, Section III shows that multiple well-connected loop-free paths offer substantially longer path lifetimes than sets of disjoint paths. Based on these results, Section IV illustrates a multipath routing approach in which node or edge disjoint paths are not enforced, using the DOS [19] routing protocol as an example. Section V summarizes the implementation of DOS used in the simulation study presented in Section VI, which compares the path distributions of our loop-free on-demand routing protocol and shows that we can maintain between 1.2 and 1.5 paths per hop, without any special path maintenance mechanisms. In 100-node simulations, the multipath scheme has about 1/3 the network load of min-hop multipath and a slightly higher delivery ratio. II. P RIOR W ORK In the literature, there are several types of disjoint paths. In two node disjoint paths, P 1 and P 2 , there is no common nodes except the first (source) and last (destination). In link disjoint paths, there are no common edges, though there may be common nodes. P 1 = {s, a, b, c, t} and P 2 = {s, m, b, n, t} are two link-disjoint paths, although they share the node b. There are also zone disjoint paths, which try to keep paths separated by some number of hops. Two “maximally”