I. INTRODUCTION

Mobile Ad-hoc Networks (MANETs) have concerned a lot of curiosity in the research community. In Manet several intermediate nodes take the responsibility of relaying information from one node to another. They also act as a router to discover and maintain route information within the network. The Ad Hoc On-demand Multi path Distance Vector (AOMDV), Ad Hoc On demand Distance Vector(AODV) and Dynamic Source Routing (DSR) are the most popular reactive routing protocols [1] for MANETs. In the reactive routing also known as on-demand routing protocol, a route is only requested when needed.

When AODV [2] needs to establish routing, the source node broadcasts a routing to ask for the RREQ grouping at first, which including the destination node address, the destination node serial number, the broadcast serial number, the source node address, the source node serial number, previous hop address and hop number.

When the intermediate nodes received RREQ, at first it should build up reverse routing according to the information provided by this RREQ, and then look for the routing table of its own, as soon as effective routing to the destination node is discovered, sending response RREP packet by reverse routing, the RREP packet including the source node address, the destination node address, the serial of destination node, hop number and survive time. If no effective routing to destination node is found, then broadcasting the RREQ to the neighbor nodes until the RREQ arrives the destination node, which generates RREP packet, and passes the RREP to the source node along the established reverse routing. When identical RREQ has various different RREP, the source node will choose the routing with the biggest destination node serial number, or choosing the routing with the smallest hop number when the destination node has the same serial number. Thus the routing is established and it can be used in its term of validity. When the source nodes and the destination nodes transmit data along the established routing, if routing has abruption, the upstream node at the place of the abruption will launch the source repair or local repair according to the relative position to the destination node.

Ad-hoc On-demand Multi path Distance Vector Routing (AOMDV) [3, 4] protocol is an extension to the AODV protocol for computing multiple loop-free and link disjoint paths. The routing entries for each destination contain a list of the next-hops along with the corresponding hop counts. All the next hops have the same sequence number. This helps in keeping track of a route. For each destination, a node maintains the advertised hop count, which is defined as the maximum hop count for all the paths, which is used for sending route advertisements of the destination. Each duplicate route advertisement received by a node defines an alternate path to the destination. Loop freedom is assured for a node by accepting alternate paths to destination if it has a less hop count than the advertised hop count for that destination. Because the maximum hop count is used, the advertised hop count therefore does not change for the same sequence number. When a route advertisement is received for a destination with a greater sequence number, the next-hop list and the advertised hop count are reinitialized.

AOMDV can be used to find node-disjoint or link-disjoint routes. To find node-disjoint routes, each node does not immediately reject duplicate RREQs. Each RREQs arriving via a different neighbor of the source defines a node-disjoint path. This is because nodes cannot be broadcast duplicate RREQs, so any two RREQs arriving at an intermediate node via a different neighbor of the source could not have traversed the same node. In an attempt to get multiple link-disjoint routes, the destination replies to duplicate RREQs, the destination only replies to RREQs arriving via unique neighbors. After the first hop, the RREPs follow the reverse paths, which are node disjoint and thus link-disjoint. The trajectories of each RREP may intersect at an intermediate node, but each takes a different reverse path to the source to ensure link disjoint ness. The advantage of using AOMDV is that it allows intermediate nodes to reply to RREQs, while still selecting disjoint paths. But, AOMDV has more message overheads during route discovery due to increased flooding and since it is a multipath routing protocol, the destination replies to the multiple RREQs those results are in longer overhead.

In DSR [5] to establish a route it sends route request packet to all nodes in the network, where Route Request packet is a broadcast packet. After receiving the RREQ packet the intermediate nodes will broadcast the packet to its neighbors if they have not forwarded already. RREQ packet contains sequence number and the path it travelled on its header. DSR uses route-cache at intermediate nodes. Route cache is a memory that stores all information extracted from the source route contained in the data packet. On receiving the RREQ it responds to the source node with a unicast packet in the reverse path of RREQ packet. In DSR, once the route is established between source and destination node the sender specifies the complete path on the packet header that the packet needs to traverse in that route to reach the destination. Once the link is broken between nodes Route Error messages are generated and sent to all nodes in the network. It maintains multiple routes per destination.

Consequently, this paper evaluates the performance of AOMDV, AODV and DSR using an ns-2 simulator.

II. SIMULATION ENVIRONMENT:

The simulations were performed using Network Simulator 2 [5] (NS-2.35) in Linux based Fedora 15 Operating System. The mobility simulation Area of 200mx200m (small Area), 500mx700m (Middle Area) and 1200mx1500m (Large Area) taking 25, 50 and 100 nodes with 4.0m/sec as a maximum speed and pause times four. We generate different scenario file and run the simulation. The trace file created by each simulation is stored. The packet size for the simulation remains 512 byte with the data traffic as CBR. Simulation time for the entire scenario was 300sec.

NS-2.35 is chosen as the simulation tool because NS-2 supports networking research and education. NS-2 is suitable for designing new protocols, comparing different protocols and traffic evaluations. NS-2 is developed as a collaborative environment. It is distributed freely and is open source.

III.PERFORMANCE METRICS:

We consider two major performance metrics to compare the AOMDV, AODV and DSR routing protocol.

A. Packet Delivery Fraction:

The packet delivery ratio (PDR) is defined as the fraction of all the received data packets at the destinations over the number of data packets sent by the sources. It is the ratio of data packets delivered to the destination to those generated by the sources. It is calculated by dividing the number of packet received by destination through the number packet originated from source. PDR can be obtained with the formula mentioned below:

Packet Delivery Ratio = Total data packets received/ Total data packets sent

B. Average End-to-End Delay:

The packet end-to-end delay (EED) is the time of generation of a packet by the source up to the destination reception. So this is the time that a packet takes to go across the network. This time is expressed in sec. Hence all the delays in the network are called packet end-to-end delay, like this includes all possible delay caused by buffering during route discovery latency, queuing at the interface queue, retransmission delay at the MAC, propagation and transfer time. The formula given under can be used to arrive this parameter:

Average end-to-end delay = (time received –time sent)/total data packets received.

IV.RESULT ANALYSIS AND DISCUSSION:

In this Section, we compare the three reactive routing protocols. To evaluate performance of AOMDV, AODV & DSR routing protocols in same simulation environment with different number of nodes, we collect the entire trace file generated by simulation of these three protocols. We use AWK program to calculate performance metrics from trace file. The simulation results are shown in the following section in the form of graphs.

Fig. 1 Packet Delivery Fraction for Small Area Simulation

Fig. 2 Average End to End Delay for Small Area Simulation

From the above Fig 1 and 2 the observable percentage of PDR in small area is quiet acceptable by every protocol. The Average End-to-End Delay is observed very low by AOMDV with 25 and 100 number of nodes but with 50 nodes DSR performs better compared to other protocols.

Fig. 3 Packet Delivery Fraction for Middle Area Simulation

Fig. 4 Average End to End Delay for Middle Area Simulation

From the above Figure 3 and 4 we observe that in Middle area again the AOMDV gives better PDR with compare to AODV and DSR with 25 and 50 nodes but with 100 number of nodes AODV is acceptable. The Average End-to-End Delay is observed very low by AOMDV compared to other protocol results which are still is acceptable.

Fig. 5 Packet Delivery Fraction for Large Area Simulation

Fig. 6 Average End to End Delay for Large Area Simulation

From the Fig 5 and 6, in case of PDF, it can be seen that AOMDV has an excellent performance over other and DSR perform poor with a few number of nodes. The Average End-to-End Delay is still observed very low by AOMDV compared to other protocol results.

V. CONCLUSION AND FUTURE WORK:

In this comparative study of specified routing protocols in MANET environment, certain significant and realistic approaches of Ad hoc networks are systematically examined. Moreover, the representations of different areas along with numbers of nodes have generated with numerous practical results. The obtained results could be used for the assortment and selections of routing protocols for specified domains.We conclude that AOMDV is better than AODV and DSR. AOMDV outperforms AODV and DSR due to its ability to search for alternate routes when a current link breaks down. With alternate route discovery mechanism, AOMDV is much more efficient when it comes to packet delivery fraction and Average End to End Delay.

In addition, parameters for future work may include network fragmentation, Quality of Service (QoS) issues, reliability check, security concerns, and efficient resource utilization. Several other routing protocols such as proactive and hybrid routing protocols may be considered for the evaluation of routing protocols.

VI. REFERENCES:

[1] Nidhi S Kulkarni, Balasubramanian Ramant, and Indra Gupta, “On Demand Routing Protocols for Mobile Ad Hoc Networks: A Review”, IEEE International/Advance Computing Conference (IACC) Patiala, India, March 2009

[2] C.E. Perkins, E.M. Belding-Royer, and S.R. Das, "Ad Hoc On-Demand Distance Vector (AODV) Routing," http://www.ietf.org/rfc/ rfc3561.txt, July 2003. RFC 3561.

[3] Marina, M. K. and Das, S. R., “On-demand Multipath Distance Vector Routing for Ad Hoc Networks,” Proc. of 9th IEEE Int. Conf. On Network Protocols, pp.14-23 (2001).

[4] YuHua Yuan, HuiMin Chen, and Min Jia, “An Optimized Ad-hoc On-demand Multipath Distance Vector (AOMDV) Routing Protocol”, Asia-Pacific Conference on Communications, Perth, Western Australia, 2005

[5] David B. Johnson, David A. Maltz, Yih-Chun Hu, ”The Dynamic Source Routing Protocol for Mobile AdHoc Networks (DSR)”, draft-ietfmanet- dsr- 10.txt, July 2004.

[6] NS-2. Available from: http://www.isi.edu/nsnam/ns/>.

Received on 02.03.2013 Accepted on 28.03.2013

Research J. Science and Tech 5(3): July- Sept., 2013 page 343-346