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IEEE 802.11 MAC protocol is the de facto standard for wireless local area networks (LANs), and has also been implemented in many network simulation packages for wireless multi‐hop ad hoc networks. However, it is well known that, as the number of active stations increases, the performance of IEEE 802.11 MAC in terms of delay and throughput degrades dramatically, especially when each station's load approaches its saturation state. To explore the inherent problems in this protocol, it is important to characterize the probability distribution of the packet service time at the MAC layer. In this paper, by modeling the exponential backoff process as a Markov chain, we can use the signal transfer function of the generalized state transition diagram to derive an approximate probability distribution of the MAC layer service time. We then present the discrete probability distribution for MAC layer packet service time, which is …