A. Helmy et al. (Eds.): MMNS 2006, LNCS 4267, pp. 37 – 48, 2006. © IFIP International Federation for Information Processing 2006 Link Available Bandwidth Monitoring for QoS Routing with AODV in Ad Hoc Networks Stephane Lohier 1 , Yacine Ghamri Doudane 2 , and Guy Pujolle 1 1 LIP6 - University of Paris VI, 8, rue du Capitaine Scott, 75015 Paris – France 2 IIE-CNAM, 18, allée Jean Rostand, 91025 Evry Cedex – France stephane.lohier@lip6.fr, ghamri@iie.cnam.fr, guy.pujolle@lip6.fr Abstract. Due to bandwidth constraint and dynamic topology of mobile ad hoc networks, supporting Quality of Service is a challenging task. In this paper we present a solution for QoS routing based on an extension of the AODV reactive routing protocol that deals with bandwidth monitoring. The solution uses an IEEE 802.11 MAC layer as the underlying technology and the QoS routing decision is based on simple but accurate measurements, at the MAC layer, of the available bandwidth on each link of the route. In addition, to allow a QoS loss recovery, a notification mechanism is used to inform the source about bandwidth degradation on a link. This reactive solution using standard protocols is adapted to small and dynamic ad hoc networks. A complete simulation set shows that, with the proposed QoS routing protocol, bandwidth on a route is significantly improved without overhead. Keywords: QoS routing, ad hoc, AODV, IEEE 802.11. 1 Introduction Throughputs reached today by mobile ad hoc networks based on the IEEE 802.11b and 802.11g standards [1-2] enable the execution of complex applications (video conference, distribution of multimedia flows…). However, these applications consume significant amounts of resources and can suffer from an inefficient and unfair use of the wireless channel. Therefore, new specific QoS solutions need to be developed taking into account the dynamic nature of ad hoc networks. Since these networks should deal with the limited radio range and mobility of their nodes, we believe that the best way to offer QoS is to integrate it in routing protocols. These protocols will have to take into consideration the QoS required by the applications, such as bandwidth constraints, in order to select the adequate routes. In our current work, a new available bandwidth monitoring technique is proposed. This monitoring is integrated to the routing process. It acts on each link allowing determining if a particular bandwidth demand can be granted or not. In addition, bandwidth monitoring allows detecting, after the QoS route is traced, if the available bandwidth is degraded on a particular link and thus leading to QoS loss on the route using the concerned link. In that case, a QoS loss recovery mechanism is triggered to inform the source which will be able to start a new QoS route search.