IEEE has standardized 802.11 protocol for wireless local area networks. The 802.11 MAC standard specifies two access mechanisms, the Distributed Coordination Function (DCF) and Point Coordination Function (PCF). DCF is considered as the basic MAC mechanism, based on the Carrier Sensing Multiple Access with Collision Avoidance (CSMA-CA) protocol, which is introduced to avoid the collision. The main problem with 802.11 MAC layer is the implementation defects of DCF. The Distributed Coordination Function (DCF) in the IEEE 802.11 standard preserves fairness for all clients at the frame level.