Infoscience

Report

On Cheating in CSMA/CA Ad Hoc Networks

CSMA/CA protocols rely on the random deferment of packet transmissions. Like most other protocols, CSMA/CA was designed with the assumption that the nodes would play by the rules. This is important, since the nodes themselves control their random deferment. However, with the higher programmability of the network adapters, the temptation to tamper with the software or firmware is likely to grow; in this way, a user could obtain a much larger share of the available bandwidth at the expense of other users. We use a game-theoretic approach to investigate the problem of the selfish behavior of nodes, specifically geared towards the most widely accepted protocol in this class of protocols, IEEE 802.11. We show that a selfish and non-cooperative behavior by a small population of (two or more) cheaters leads to a network collapse. We argue that this provides an incentive for cheaters to cooperate with each other. However, explicit cooperation among nodes is clearly impractical. By applying the model of dynamic games borrowed from game theory, we derive the conditions for the stable and optimal functioning of a population of cheaters. We use this insight to develop a simple, localized and distributed cheating protocol that needs no explicit cooperation between cheaters or \textit{a priori} knowledge about the total number of nodes/cheaters in the system. We show that the scheme successfully guides multiple selfish nodes to a Pareto-optimal Nash equilibrium.

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