A mobile ad hoc network (MANET) is an autonomous network that consists of mobile nodes that communicate with each other over wireless links. In the absence of a fixed infrastructure, nodes have to cooperate in order to provide the necessary network functionality. One of the principal routing protocols used in Ad hoc networks is AODV (Ad hoc On demand Distance Vector) protocol. The security of the AODV protocol is compromised by a particular type of attack called ‘Black Hole’ attack In this attack a malicious node advertises itself as having the shortest path to the node whose packets it wants to intercept. To reduce the probability it is proposed to wait and check the replies from all the neighboring nodes to find a safe route. Our approach to combat the Black hole attack is to make use of a ‘Fidelity Table’ wherein every participating node will be assigned a fidelity level that acts as a measure of reliability of that node. In case the level of any node drops to 0, it is considered to be a malicious node, termed as a ‘Black hole’ and is eliminated. Computer simulation using GLOMOSIM shows that our protocol provides better security and also better performance in terms of packet delivery than the conventional AODV in the presence of Black holes with minimal additional delay and Overhead.

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Abstract-Ad hoc wireless networks consist of mobile network without base stations, and are characterized by a host in a highly dynamic network topology. The topology changes frequently due to host migration, signal interference and power outages, making the route maintenance a challenging consideration in designing routing protocols. Most of the existing protocols perform an end-to-end route discovery to establish a new connection for the communication during link breaks. Such route repair mechanism causes high control overhead and long packet delay in a dense network. In this paper, we propose an enhanced proactive route maintenance protocol, where a node that is likely to cause link error, as a preventive measure, hands off routing information to a new node by monitoring the signal strength of the received signals. The proposed protocol aims to reduce the probability of route breakage and hence reduces the control overhead and latency, and increases the packet delivery ratio. Through simulation, we show that the proposed protocol is simple, robust and effective.Index Terms-Dense MANETs, RSSI, link stability, apriori maintenance.

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