Compelling features of wireless local area networks (WLANs), put a variety of wireless service demands in place. In order to adjust system parameters to fulfill specific needs of different applications, a mathematical description of the system turns to be helpful. The inherent complexity of the wireless access, makes this description very challenging. We propose a new performance model for the IEEE 802.11 WLAN in ad hoc mode. The ad hoc mode has been chosen since we eventually aim at interconnected WLAN clusters where no base station exists. The model is based on the presentation of the system with a pair of one-dimensional state diagrams which can easily accommodate variations of many input parameters. The corresponding state variables are contention window size and buffer occupancy of each user in the system. The input parameters considered are: packet fragmentation factor, buffer size, and maximum allowable number of retransmissions. However, the approach taken is capable of ingesting many other probable parameters of interest. System performance criteria under study are: throughput, delay, and probability of fail to deliver. The last two are crucial for real-time applications.