Partial-Disjoint Multipath Routing for Wireless Ad-hoc Networks Haseeb Zafar, David Harle, Ivan Andonovic Department of Electronic & Electrical Engineering University of Strathclyde Glasgow, G1 1XW, UK [haseeb, d.harle, i.andonovic]@eee.strath.ac.uk Mahmood Ashraf Institute of Communication Technologies Pakistan Telecommunication Company Limited Islamabad, Pakistan mahmood@ictech.edu.pk Abstract—On-demand multipath routing in wireless ad-hoc networks can be effective in achieving load balancing over the network and in providing a degree of resilience to route failures. A Shortest Multipath Source Routing (SMS) protocol is proposed - a multipath extension to DSR - supporting multimedia applications. The protocol has two novel aspects compared to other on-demand multipath routing protocols: it achieves shorter multiple partial-disjoint paths and allows rapid recovery of route breaks Simulation results show that SMS outperforms the competing protocols with respect to a number of key performance metrics. Keywords- ad-hoc networks; multipath routing; multimedia applications; shortest multipath source routing; partial-disjoint I. INTRODUCTION Wireless Ad-hoc Networks (MANETs) [1] are characterized by the lack of infrastructure and frequent topological changes. On-demand routing protocols have been widely studied because they consume less bandwidth than their pro-active counterparts. Single-path, on-demand routing protocols [2][3] rely on a uni-path route for each data session. In the case of a failure of any active link between source and destination, the routing protocol must invoke a route discovery process and, in so doing, additional delay is incurred and overhead increase. On-demand multipath routing protocols [4][5][6][7] can alleviate these problems by establishing multiple paths between a source and a destination within a single route discovery process. The performance of multipath routing protocols often start to degrade in terms of end-to-end delay and routing overheads when mobility rates and traffic loads increase; a result of both longer and stale routes [8]. Motivated by such limitations, a Shortest Multipath Source (SMS) routing protocol, an extension to the DSR [2], is proposed that reduces end-to-end delay and routing overheads incurred when recovering from route breaks. The paper is organized as follows. Section-II presents the proposed scheme. Simulation results derived from NS-2 [9] models are presented in Section III. Concluding remarks are made in Section IV. II. THE PROPOSED SCHEME Based on short-comings in existing multipath routing protocols [8], a Shortest Multipath Source (SMS) routing protocol, an extension to the DSR [2], is proposed. SMS builds multiple partial-disjoint paths from source to destination in order to mitigate the overhead of additional route discoveries and to recover quickly from route breaks. As a consequence, improved performance in terms of goodput, end-to-end delay and routing overheads is obtained. SMS computes multiple partial-disjoint paths that will bypass at least one intermediate node on the primary path. An example that illustrates the computation of partial-disjoint paths is shown in Figure 1. In case of a link failure between A and B (Figure 2), the source node will search for an alternate route that does not contain node B. In this case, an alternative route between source and destination is S-A-G-C-D. The major advantage of such a protocol is that the shortest alternative routes by contrast to the routes computed using either link-disjoint or node-disjoint paths are selected. Figure 1 Partial-disjoint multiple paths Figure 2 Selection of alternative path in case of link failure A. Route Discovery Route Discovery has two basic phases; route request propagation and route reply. A.1 Route Request Propagation When a node seeks to communicate with another node, it searches its cache to find any known routes to the destination. If no routes are available, the node initiates route discovery by flooding route-request packet, containing an ID which, along with source address, uniquely identifies the current discovery. The SMS scheme introduces a novel approach to reduce broadcast overhead. Each node records the ID of route-request packet and the number of hops the route request traversed from the source node. Nodes use this information to re- broadcast duplicate route-request packets only if: number of hops ≤ last hop-count recorded (1) S E G F A C H B D I J S E G F A C H B D I J SABCD SEBCD SAGCD SABJD SFHCD 32nd IEEE Conference on Local Computer Networks 0742-1303/07 $25.00 © 2007 IEEE DOI 10.1109/LCN.2007.84 258