1 International Journal of Communication Networks and Information Security (IJCNIS) Vol. 4, No. 1, April 2012 QoS-aware Multipath Routing Scheme for Mobile Ad Hoc Networks Haseeb Zafar 1,2 , David Harle 1 , Ivan Andonovic 1 , Laiq Hasan 2 and Amjad Khattak 3 1 Department of Electronic & Electrical Engineering University of Strathclyde, Glasgow, UK 2 Department of Computer Systems Engineering University of Engineering & Technology, Peshawar, Pakistan 3 Department of Electrical Engineering University of Engineering & Technology, Peshawar, Pakistan Contact Email Address: haseeb@eee.strath.ac.uk Abstract: Providing Quality of Service (QoS) support in Mobile Ad Hoc Networks (MANETs) is a particularly active research area with a number of proposals being made to support real-time applications that are based upon the interaction between the routing scheme and a QoS provisioning mechanism. This paper builds upon such ideas and presents QoS-aware Shortest Multipath Source (Q- SMS) routing scheme that have been shown to offer significant network improvement when compared to previously proposed schemes. Q-SMS essentially modifies the previously proposed SMS scheme to explicitly provide QoS assurance. The new proposed scheme allows nodes to obtain and then use estimation of the residual capacity to make appropriate admission control decisions. The performance differentials are investigated using Network Simulator 2 (NS-2). Results demonstrate the merits of the proposed scheme with a 16% increase in goodput while end-to-end delay is reduced by 37% when compared with SMS and the necessity of QoS-aware multipath routing schemes in MANETs becomes more apparent. Keywords: Mobile Ad Hoc Networks, multipath routing, Network Simulator 2, Quality of Service, Shortest Multipath Source. 1. Introduction Routing schemes have prompted a great deal of interest from the beginning of Mobile Ad Hoc Network (MANET) [1] research until the present time. Early work [2–4] focused on finding feasible routes without considering information about the network status. In addition, without knowing the bottleneck capacity or throughput, the source may send more data than the bottleneck node on the route can accommodate. The overloaded node ultimately drops data which wastes capacity and unnecessarily consumes energy. Also, time is expended in transmitting such data. Therefore, data that eventually reaches its destination would have had to wait longer in packet queues, resulting in a significantly increased delay. Although this may be acceptable for data only applications, many real-time applications require Quality of Service (QoS) support from the network. Possible QoS support can be achieved by finding a route to satisfy the application requirements. QoS-aware routing takes into consideration multiple QoS requirements, link dynamics, as well as the implication of the selected routes on network utilization, rendering QoS routing a particularly challenging problem. However, the unique features of MANETs, namely dynamically varying network topology, imprecise state information, lack of central coordination, error-prone shared radio channel, hidden terminal problem and time-varying capacity exacerbate the already complex routing problem [4]. More importantly, node mobility causes frequent failure and reactivation of links, effecting a reaction to the changes in topology from the network’s routing, thus increasing network control traffic and saturating the already congested links. Hence, all these aspects necessitate a cost-effective QoS-aware routing scheme. The majority of the QoS-aware routing schemes proposed in the literature have focused on providing QoS based on two metrics: capacity (throughput) and delay [5–22]. Of these metrics, the most commonly used is capacity. This is possibly because most real-time applications require some degree of guaranteed throughput in addition to other constraints. A number of schemes have been previously proposed that estimate residual capacity derived from window-based measurements of channel estimation. However, to increase the user's perceived QoS, multipath routing techniques can be used to improve the previously proposed unipath solutions. Table 1 summarizes and compares the main characteristics of selected QoS-aware routing schemes. In this paper, a new QoS-aware routing scheme is proposed which is based on Shortest Multipath Source (SMS) routing scheme [23]. The novel part of the proposed scheme is a simple additional mechanism to estimate residual capacity in IEEE 802.11-based ad hoc networks that provides better than best-effort service. It is shown through simulation-based evaluation to provide enhanced utilization estimation and thus better available capacity based admission control. The remainder of the paper is organized as follows. Section 2 presents an overview of the SMS routing scheme. Section 3 presents the proposed QoS-aware routing scheme for MANETs. In section 4, simulation environment based on NS-2 [24] is proposed. Section 5 discusses the simulation results and concluding remarks are made in Section 6.