Impact of node density and mobility on the performance of AODV and DSR in MANETS K. Amjad, A.J. Stocker Radio Systems Research Group, Dept. of Engineering, University of Leicester, U.K. ka167@le.ac.uk, sto@ion.le.ac.uk Abstract—Mobile ad-hoc networks (MANETS) are formed by a collection of mobile nodes that have the ability to form a communication network without the help of any fixed infrastructure. Because of the nature of these networks, routing protocols play a prominent role in their scalability and overall performance. Due to limited radio transmission range, multiple hops may be required in order to exchange data among the communicating nodes. So, a key requirement of any efficient routing protocol is to find a route between two communicating nodes quickly and with low bandwidth overheads. This study inspects two MANET protocols (i.e. Ad-hoc On-demand Distance Vector routing (AODV) and Dynamic Source Routing (DSR)) and examines their performance based on variation of node density and mobility using mobility models such as Random Way Point (RWP) and Random Way Point with Attractions (RWP-ATTR). The performance is determined on the basis of packet delivery ratio, normalized routing load, throughput and average end-to-end delay with varying node density and mobility. DSR with higher node density shows an extreme degradation in performance. The non-uniform node distribution that occurred for RWP has significant impact on performance results for both protocols. I. INTRODUCTION A mobile ad-hoc network is a collection of mobile platforms that form a dynamic infrastructure-less communication network wherever it is required. The absence of a fixed infrastructure means that the communicating nodes in the network must also handle routing. Quick and easy establishment of such networks make them feasible to use in military, disaster area recovery and in other environments where no infrastructure exists or it has been destroyed. Routing is a well studied feature of such networks because mobile nodes may move in various directions, which can cause existing links to break and the establishment of new routes. The mobility (i.e. how nodes move) of mobile nodes plays an important role on the performance of routing protocols. Routes between two communicating nodes may consist of multiple hops through other nodes in the network. Therefore, finding and maintaining routes in MANET is nontrivial. Due to bandwidth constraints, it is readily understandable that an on demand approach (i.e. the route discovery is initiated only if there is a demand for communication) is often used in wireless ad-hoc network scenarios. The most famous routing approach in ad-hoc networks is that of reactive protocols and the most popular on-demand routing algorithms are Ad-hoc On-Demand Distance Vector routing (AODV) [1] and Dynamic Source Routing (DSR) [2]. So, since they are widely used, this paper discusses the impact of random waypoint and a variation of random waypoint with attractions on the performance of AODV and DSR with varying node density and mobility patterns. The network simulator ns-2 [3] is a commonly used tool for MANETS protocol evaluation. In this study, ns- 2.33 is used for all simulation results. II. OVERVIEW OF ROUTING PROTOCOLS A. Dynamic Source routing (DSR) DSR uses source routing and caching [4] where the sender node includes the complete hop-by-hop route to the destination node in the packet header and routes are stored in a route cache. When a node wants to communicate with another node to which it does not know the route, it initiates a route discovery process with a flooding request of route request (RREQ) packets. Each node receiving the RREQ packets retransmits it unless it is the target node or it knows the route to the destination from its cache. Such a node replies to the RREQ message with a route reply (RREP) packet. The RREP packet takes the traverse path back to the source node established by the RREQ packet. This route is stored in the source node cache for future communication. If any link of this route is broken, the source node is informed by a route error (RERR) packet and this route is discarded from cache. Intermediate nodes store the source route in their cache for possible future use. B. Ad-hoc On-Demand Distance Vector Routing (AODV) AODV is a destination based reactive protocol. This protocol inherits the feature of route discovery from DSR. However, AODV resolves the problem of large headers found in DSR. This problem can cause significant performance degradation especially when the actual data contents are small. AODV maintains routing tables on the nodes instead of including a header in the data packet. The source node initiates the route discovery process in the same way as in DSR. An intermediate node may reply with a route reply (RREP) only if it knows a more recent path than the one known by the sender node to the destination. A destination sequence number is used to indicate how recent the path is as follows. A new route request generated by the sender node is tagged with a higher sequence number and an intermediate node that knows the route to the destination with a smaller sequence number cannot send the RREP message. Forward links are setup when a RREP travels back along the path taken by RREQ. So the routing table entries are used to forward the data packet and the route is not included in the packet header. If an intermediate node is unable to forward the packet to the next hop or destination due to link failures, it generates the route error (RERR) message by tagging it with a higher destination sequence number. When the sender node receives the RERR message, it initiates a new route discovery for the destination node. 978-1-86135-369-6/10/$25.00 ©2010 IEEE AHN-3 61 CSNDSP 2010