Behaviour of Adhoc Routing Protocols in
Different Terrain Sizes
K.E.Kannammal, Associate Professor, Department of Computer Science and Engineering, Sri Shakthi Institute of Engineering and Technology, Coimbatore
K.E.Eswari, Assistant Professor, Department of Master of Computer Applications, Nandha Engineering College, Erode
Abstract:- An Adhoc network is a collection of nodes forming a temporary network with out the use of any additional infrastructure and no centralized control. In recent years, a variety of new routing protocols targeted but little performance information on each protocol. We compare the performance of the three prominent routing protocols for mobile ad hoc networks, Adhoc On Demand Distance Vector (AODV), Destination Sequenced Distance Vector (DSDV) and Dynamic Source Routing (DSR). In this paper we have made comparative study of the performance of the protocols for varying terrain sizes and pause time using Network Simulator-2[1]. We have compared the performance of the protocols by taking three metrics, Packet Delivery Ratio, End-to-End Delay, Routing overhead using varying terrain sizes. The simulation result shows that the performance of the protocols decreases as the terrain size increases.
Keywords—Ad hoc Networks, Average Delay, Performance Analysis, Routing Protocols, Simulation. 1. INTRODUCTION
Ad-hoc networks are formed in situations where mobile computing devices require networking applications while a fixed network infrastructure is not available or not preferred to be used. In these cases mobile devices could setup a possibly short-lived network for the communication needs of the moment, in other words, an ad-hoc network. Ad-hoc networks are decentralized, self organizing networks and are capable of forming a communication network without relying on any fixed infrastructure. Adhoc Networks are very useful in emergency search-and rescue 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 three categories as shown in fig 1.
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.
Hybrid Protocols The hybrid routing protocols try to combine proactive and reactive approaches based on certain conditions. ZRP for example defines a zone around nodes. Within that zone proactive routing is used, outside of it nodes use reactive routing.
2. PROTOCOLS DESCRIPTION
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 protocol (DSR)
DSR is anon-demand routing protocol. The major difference between DSR and the other on demand routing protocols is that, it is beacon less and hence does not require periodic hello packets. Consider a source node that does not have a route to the destination. When it has a data packet to be sent to that destination, then it initiates a Route Request packet [3]. This Route Request is flooded throughout the network. Each node upon receiving a Route Request broadcasts the packet to its neighbors if it has not forwarded already or if the node is not the destination node. Each Route Request carries a sequence number generated by the source node and the path it has traversed. A node, upon receiving a Route Request packet, checks the sequence number on the packet before forwarding it. The packet is forwarded only if it is not a duplicate Route Request packet. The sequence number on the packet is used to prevent loop formations and to avoid multiple transmissions of the same Route Request by an intermediate node, which receives it through multiple paths. Thus, all the nodes except the destination node, forwards a Route Request packet during the route construction phase. A destination node upon receiving the Route Request packet, replies to the source node through the reverse path the Route Request packet had traversed. Several optimization techniques have been incorporated into the basic DSR protocol to improve the performance of the protocol like caching the routes at intermediate nodes. The route cache is populated with the routes that can be extracted to forward the data packet. This cache information is used by the intermediate nodes to reply to the source when they receive a Route Request packet and if they have a route to the corresponding destination.
DSDV (Destination Sequenced Distance Vector)
3. SIMULATION MODEL AND EVALUATION METRICS Simulation Environment
The simulation experiment is carried out in LINUX. The detailed simulation model is based on network simulator-2 (ver-2.31), 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: 1200 m ×600 m and 2000mx 1000m field with 150 nodes. Here, each packet starts its journey from a random location to a random destination with a randomly chosen speed (uniformly distributed between 0–10 m/s). Once the destination is reached, another random destination is targeted after a pause[4]. The pause time, which affects the relative speeds of the mobiles, is varied. Simulations are run for 30 simulated seconds. Identical mobility and traffic scenarios are used across protocols to gather fair results. Mobility models were created for the simulations using 150 nodes, with pause times of 10, 20, 30, 40, 50 seconds, maximum speed of 10 m/s and simulation time of 30 secs. The parameters are shown in table.1.
PARAMETERS VALUES Simulation time 30 sec Number of nodes 150
Pause time 10,20,30,40,50 sec Size of topography 1200 X 600, 2000 X 1000 Traffic Type Constant Bit Rate (CBR) Maximum Speed 10m/s
Network Load 4 pkts/sec
Mobility Model Random Waypoint Model
Table 1: Scenario for NS-2 topology
Metrics for Performance Evaluation
In this section, we present performance metrics that have been proposed for (or used in) the performance evaluation of an ad-hoc network protocol. The following metrics are applied to comparing the protocol performance. Some of these metrics are suggested by the MANET working group for routing protocol evaluation [5,6,7].
Packet delivery ratio: Packet Delivery Ratio is defined as the ratio of the packets received by the CBR sinks at the destinations over the packets generated from the CBR sources. Nodes will stop a” pause-time” amount before moving to another destination point. In the simulation we vary the pause time from 10-50 sec.
Routing packet overhead: Routing Packet overhead RPO is the total number of transmissions routing packets transmitted during the simulation. For packets sent over multiple hops, each transmission of the packet (each hop) counts as one transmission.
4. SIMULATION RESULTS
This section presents a comparative analysis of the performance metrics generated from all simulations, evincing general and relevant aspects of the evaluated routing protocols in the diversity of terrain sizes and pause time that can occur over DSDV, AODV and DSR routing protocols
Comparison between DSDV, AODV and DSR
Performance comparison of the protocols, an attempt was to compare all of the three protocols under the same simulation environment [8, 9], we conducted simulations using different pause times, while generate a fixed number of traffic sources depend on constant bit rate for packets, and will try to discuss the behavior of our routing simulation protocols depend on a varying pausing time and variable terrain size. We will consider a wide range of pause time for our mobile nodes from 10, 20,30,40,50 m/s. The figures from (2 to 7) explain and highlight the relative performance of the three routing protocols DSDV, AODV and DSR depend on some metrics to our simulations.
Packet Delivery Ratio
This metric which we call the ratio of delivered packets is an important as it describes the loss rate that will be seen by the transport protocols, which in turn affects the maximum throughput that the network can support.
The fig.2 and 3 show the packet delivery fraction in different terrain region in 1200 m x 600m and 2000m x 1000m.The performance of the protocols decreases as the terrain size increases. This is due to the reason when area increases then nodes becomes sparse due to which route discovery and route maintenance process takes more time. Then the ratio calculated by dividing the number of packets received by the destination through the number of packets originated by the application layer of the source (i.e. CBR source) will also affected and as a result of which average performance of both protocols degrades.
Figure 2.Packet Delivery Rate for 1200 x 600 Figure 3.Packet Delivery Rate for 2000 x 1000
Routing packet overhead
Figure 4.Routing packet overhead-1200m x 600m Figure.5.Routing packet overhead 2000mx 1000m
Average end to end data delay
In Figures 6 and 7, it can be seen that increasing in terrain size results in significant change in the average end-to-end delay of the protocols. This is because when a node receives a route request for which it has the answer in its routing table, it immediately replies with the route rather than forwarding it to the destination. The source can now start to communicate with the destination.
5.CONCLUSION
The area of ad-hoc networking has been receiving increasing attention among researchers in recent years, as the available wireless networking and mobile computing hard-ware bases are now capable of supporting the promise of this technology. Over the past few years, a variety of new routing protocols targeted specifically at the ad-hoc networking environment have been proposed, but little performance information on each protocol and node tailed performance comparison between the protocols has previously been available.
This paper has presented a performance comparison of protocols for adhoc network routing protocol AODV, DSR and DSDV using a network simulator NS-2 with scenario consist of different terrain sizes and pause time . DSDV uses the proactive table-driven routing strategy while both AODV and DSR use the reactive on demand routing strategy. The general observation from the simulation is that for packet delivery fraction for all the three protocols are decreased as terrain size increases. The routing overhead and delay of all the three protocols are increased as terrain size increases.
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