Performance Evaluation of Ad Hoc Routing Protocols Using NS 2 Simulation 1 Performance Evaluation of Ad Hoc Routing Protocols Using NS 2 Simulation

An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. A nu mber of routing protocols like Dynamic Source Routing (DSR), Ad Hoc On-Demand Distance Vector Routing (AODV) and DestinationSequenced Distance-Vector (DSDV) have been implemented. In this project, an attempt has been made to compare the performance of two prominent on-demand reactive routing protocols for mobile ad hoc networks: DSR and AODV, along with the traditional proactive DSDV protocol. A simulation model with MAC and physical layer models is used to study interlayer interactions and their performance implications. The On-demand protocols, AODV and DSR perform better than the table-driven DSDV protocol. Although DSR and AODV share similar on-demand behavior, the differences in the protocol mechanics can lead to significant performance differentials. A variety of workload and scenarios, as characterized by mobility, load and size of the ad hoc network were simulated. The performance differentials are analyzed using varying network load, mobility, and network size. These simulations are carried out based on the Rice Monarch Project that has made substantial extensions to the ns -2 network simulator to run ad hoc simulations. Keywords— Performance, Analysis, Ad Hoc Network, AODV, DSR, DSDV, NS2. INTRODUCTION ireless networking is an emerging technology that allows users to access information and services electronically, regardless of their geographic position. Wireless networks can be classified in two types. Infrastructure Networks Infrastructure network consists of a network with fixed and wired gateways. A mobile host communicates with a bridge in the network (called base station) within its communication radius. The mobile unit can move geographically while it is communicating. When it goes out of range of one base station, it connects with new base station and starts communicating through it. This is called handoff. In this approach the base stations are fixed. Infrastructure Less (Ad hoc) Networks In ad hoc networks [5] all nodes are mobile and can be connected dynamically in an arbitrary manner. As the range of each host’s wireless transmission is limited, so to communicate with hosts outside its transmission range, a host needs to enlist the aid of its nearby hosts in forwarding packets to the destination. So all nodes of these networks behave as routers and take part in discovery and maintenance of routes to other nodes in the network. Ad hoc Networks are very useful in emergency search-andrescue operations, meetings or conventions in which persons wish to quickly share information, and data acquisition operations in inhospitable terrain. This ad-hoc routing protocols can be divided into two categories: Table-Driven Routing Protocols: In table driven routing protocols, consistent and up-t o-date routing information to all nodes is maintained at each n ode. On-Demand Routing Protocols: In On-Demand routing protocols, the routes are created as and when required. When a source wants to send to a destination, it invokes the route discovery mechanisms to find the path to the destination. AD-HOC ROUTING PROTOCOLS DESCRIPTION Destination-Sequenced Distance-Vector The Destination-Sequenced Distance-Vector (DSDV) [3] Routing Algorithm is based on the idea of the classical Bellman-Ford Routing Algorithm with certain improvements. Every mobile station maintains a routing table that lists all available destinations, the number of hops to reach the destination and the sequence number assigned by the destination node. The sequence number is used to distinguish stale routes from new ones and thus avoid the formation of loops. The stations periodically transmit their routing tables to their immediate neighbors. A station also transmits its routing table if a significant change has occurred in its table from the last update sent. So, the update is both time-driven and event-driven. W 168 Mobile and Pervasive Computing (CoMPC–2008) The routing table updates can be sent in two ways: a “full dump ” or an incremental update. A full dump sends the full routing table to the neighbors and could span many packets whereas in an incremental update only those entries from the routing table are sent that has a metric change since the last update and it must fit in a packet. If there is space in the incremental update packet then those entries may be included whose sequence number has changed. When the network is relatively stable, incremental updates are sent to avoid extra traffic and full dump are relatively infrequent. In a fast-changing network, incremental packets can grow big so full dumps will be more frequent. Ad Hoc On-Demand Distance Vector Routing (AODV) AODV [2] discovers routes on an as needed basis via a similar route discovery process. However, AODV adopts a very different mechanism to maintain routing information. It uses traditional routing tables, one entry per destination. This is in contrast to DSR, which can maintain multiple route cache entries for each destination. Without source routing, AODV relies on routing table entries to propagate an RREP back to the source and, subsequently, to route data packets to the destination. AODV uses sequence numbers maintained at each destination to determine freshness of routing information and to prevent routing loops. All routing packets carry these sequence numbers. An important feature of AODV is the maintenance of timer-based states in each node, regarding utilization of individual routing table entries. A routing table entry is expired if not used recently. A set of predecessor nodes is maintained for each routing table entry, indicating the set of neighboring nodes which use that entry to route data packets. These nodes are notified with RERR packets when the next-hop link breaks. Each predecessor node, in turn, forwards the RERR to its own set of predecessors, thus effectively erasing all routes using the broken link. In contrast to DSR, RERR packets in AODV are intended to inform all sources using a link when a failure occurs. Route error propagation in AODV can be visualized conceptually as a tree whose root is the node at the point of failure and all sources using the failed link as the leaves. Dynamic Source Routing (DSR) The key distinguishing feature of DSR [4] is the use of source routing. That is, the sender knows the complete hop by-hop route to the destination. These routes are stored in a route cache. The data packets carry the source route in the packet header. When a node in the ad hoc network attempts to send a data packet to a destination for which it does not already know the route, it uses a route discovery process to dynamically determine such a route. Route discovery works by flooding the network with route request (RREQ) packets. Each node receiving an RREQ rebroadcasts it, unless it is the destination or it has a route to the destination in its route cache. Such a node replies to the RREQ with a route reply (RREP) packet that is routed back to the original source. RREQ and RREP packets are also source routed. The RREQ builds up the path traversed across the network. The RREP routes itself back to the source by traversing this path backward. The route carried back by the RREP packet is cached at the source for future use. If any link on a source route is broken, the source node is notified using a route error (RERR) packet. The source removes any route using this link from its cache. A new route discovery process must be initiated by the source if this route is still needed. DSR makes very aggressive use of source routing and route caching. PERFORMANCE ANALYSIS Simulation Environment The simulation experiment is carried out in LINUX (FEDORA 6). The detailed simulation model is based on network simulator-2 (ver-2.31) [1], is used in the evaluation. The NS instructions can be used to define the topology structure of the network and the motion mode of the nodes, to configure the service source and the receiver, to create the statistical data track file and so on. Traffic Model Continuous bit rate (CBR) traffic sources are used. The source-destination pairs are spread randomly over the network. Only 512-byte data packets are used. The number of source-destination pairs and the packet sending rate in each pair is varied to change the offered load in the network. Mobility Model The mobility model uses the random waypoint model in a rectangular field. The field configurations used is: 500 m × 500 m field with 50 nodes. Here, each packet starts its journey from a random location to a random destination with a randomly chosen speed (uniformly distributed between 0–20 m/s). Once the destination is reached, another random destination is targeted after a pause. The pause time, which affects the relative speeds of the mobiles, is varied. Simulations are run for 100 simulated seconds. Identical mobility and traffic scenarios are used across protocols to gather fair results. Mobility models were created for the simulations using 50 nodes, with pause times of 0, 10, 20, 40, 100 seconds, maximum speed of 20 m/s, topology boundary of 500 × 500 and simulation time of 100 secs. Performance Evaluation of Ad Hoc Routing Protocols Using NS2 Simulation 169 PERFORMANCE METRICS [7] Packet Delivery Fraction The ratio of the data packets delivered to the destinations to those generated by the CBR sources is known as packet delivery fraction. Average End-to-End Delay Average end to end delay includes all possible delays caused by buffering during route discovery latency, queuing at the interface queue, retransmission delays at the MAC, and propagation and transfer times of data packets. Normalized Routing Load The number of routing packets transmitted per data packet delivered at the destination. Each hop -wise transmission of a routing packet is counted as one transmission. The fi