Abstract— In mobile ad hoc networks (MANET), broadcasting is widely used in route discovery and many other network services. The efficiency of broadcasting protocol can affect the performance of the entire network. As such, the simple flooding algorithm aggravates a high number of unnecessary packet rebroadcasts, causing contention and packet collisions. Proper use of probabilistic method can reduce the number of rebroadcasting, therefore reduce the chance of contention and collision among neighboring nodes. A good probabilistic broadcast protocol can achieve high save rebroadcast and low collision. In this paper, we propose a dynamic probabilistic approach when nodes move according to way point mobility and compare it with simple flooding AODV and fixed probabilistic scheme. Our approach dynamically set the rebroadcasting probability according to the number of nieghbors nodes distributed in the ad hoc network. Simulation results show our approach performs better than both simple flooding and fixed probabilistic flooding. Keywords—AODV, MANETs, probabilistic broadcasting, reachability I. INTRODUCTION obile ad hoc networks (MANETs) are self-organizing mobile wireless networks that do not rely on a preexisting infrastructure to communicate. Network-wide dissemination is used widely in MANETs [1] for the process of route invention, address resolution, and other network layer tasks. For example, on demand routing protocols such as ad- hoc on demand distance vector (AODV) [8] and dynamic source routing (DSR) [12] use the broadcast information in route request packets to construct routing tables at every mobile node [3]. The lively nature of MANETs, however, requires the routing protocols to refresh the routing tables regularly, which could generate a large number of broadcasting Packets at various nodes. Since not every node in a MANET can communicate directly with the nodes outside its communication range, a broadcast packet may have to be rebroadcast several times at relaying nodes in order to guarantee that the packet can reach all nodes. Consequently, an inefficient broadcast approach may generate many redundant rebroadcast packets [5]. There are many proposed approaches for broadcasting in MANETs. The simplest one is the flooding. In this technique, each mobile host rebroadcasts the packets when received for the first time. Packets that have already been received are just droped. Though flooding is simple, it consumes much network resources as it introduces a large number of duplicate messages. It leads to serious redundancy, contention and collision in mobile wireless networks, which is referred to “broadcast storm problem” [2]. In this paper, we propose a dynamic probabilistic approach for broadcast. We set the rebroadcast probability of a host according to number of neighbor nodes information. The rebroadcast probability would be low when the number of neighbor nodes are high which means host is in dense area and the probability would be high when the number of neighbor nodes are low which means host is in sparse area. Simulation results show that broadcast redundancy can be significantly reduced through the proposed approach. The rest of this paper is structured as follows. Section 2 includes the background and related work of dissemination in MANETs. Section 3 presents the proposed dynamic probabilistic approach, highlighting its distinctive features from the other similar techniques. The parameters used in the experiments and the performance results and analysis to evaluate the effectiveness and limitation of the proposed technique are presented in Section 4. Section 5 concludes the paper and outlines the future work. II. RELATED WORK This section analyses the related work which directly or indirectly aims at reducing the number of broadcast packets generated by the flooding algorithm. The high number of redundant broadcast packets due to flooding in MANETs has been referred to as the “Broadcast Storm Problem” [2]. There are five proposed flooding schemes [6] in MANETs called probabilistic, counter-based, distance-based, location- based [2] and cluster-based [2, 6]. In the probabilistic scheme, when receiving a broadcast message for the first time, a host Improving Route Discovery of Dynamic Probabilistic Flooding in On-Demand Routing Protocols for MANETs Abdalla M. Hanashi, Irfan Awan and Mike Woodward Mobile Computing, Networks and Security Research Group School of Informatics, University of Bradford, Bradford, BD7 1DP, U.K. {a.m.o.hanashi, i.u.awan, m.e.woodward}@bradford.ac.uk M 89