Two mechanisms are proposed in this paper to be incorporated with IEEE 802.11e EDCA MAC protocol for providing the QoS provisioning capability of such network. First, the call admission control function, which considers the inherent contention access feature of 802.11 MAC, aims to satisfy the QoS requirement of established higher priority connections, while protecting the minimum reserved bandwidth of traffic flows with lower priority at the same time. In addition, the proposed adaptive contention window adjustment mechanism dynamically adjusts the maximum and minimum contention window size based upon the equivalent established connection number observed by each individual access category. Such approach reduces the channel contention probability and packet access delay effectively. Performance results via simulations have shown the advantages achieved by employing these two mechanisms.