Energy-efficient jamming attack in IEEE 802.11 MAC

In wireless local area networks that use the Distributed Coordinated Function (DCF) of the IEEE 802.11 Medium Access Control (MAC) protocol, a collision may occur when two or more devices transmit simultaneously. When a collision results in failed reception of a packet, the stations involved increase their backoff window, which decreases the probability of transmission and hence that of further potential collision. A jammer trying to disrupt the communications can take advantage of this backoff mechanism to reduce the throughput of the system significantly with little energy expense. In this paper, the effect of jamming on the backoff mechanism of the IEEE 802.11 DCF is analyzed. Analytical expressions for throughput and jammer's power expenditure are derived as a function of probability of jamming. These results are experimentally verified with the help of a jammer built using commercially available IEEE 802.11 devices. It is found that under the standard DCF, the jammer's power expenditure decreases after the jamming probability increases beyond a threshold. This non-intuitive behavior constitutes a severe vulnerability of the IEEE 802.11 MAC to jamming attacks.