Thwarting Back-off Rules Violation in Tactical Wireless Ad hoc Networks

The CSMA/CA protocol is the most commonly used medium access mechanism in wireless networks. This protocol schedules properly the access to the medium among all the competing nodes. However, in a hostile environment, such as Mobile Ad Hoc Networks (MANETs), selfish or greedy nodes may prefer to decline the proper use of MAC protocol rules in order to increase their throughput at the expense of their honest neighbors. In this work, we propose a new backoff scheme that allows the neighbors of any node to detect its attempt to deliberately disobey the MAC protocol rules, by either fabricating a small backoff value or refusing to increase its contention window after an unsuccessful transmission. Our scheme uses one way function to generate the backoff values and modifies the TS frame format by piggybacking the DATA packet's CRC value and the transmission attempt. So any cheating attempt will be detected by the receiver node as well as the other neighbors of the cheater, as long as the monitoring conditions are held. Moreover, our scheme is robust against sender-receiver collusion and provides a novel reaction mechanism to punish the detected cheaters. The simulation results, in different topologies, have confirmed the efficiency of this scheme in terms of fairness index and detection rate. & copyright 2010 IEEE.