We introduce P3-DCF, a new quality of service (QoS) mechanism, within the MAC protocol in IEEE 802.11. P3-DCF enhances the distributed coordination function (DCF) for prioritized service in IEEE 802.11. A novel function, the per-packet priority function, integrated to DCF establishes not only a per-flow differentiation but schedules the packets with an earliest deadline first discipline as well. The simulations carried out show that the enhanced MAC protocol satisfies the maximum tolerable latency of real-time traffics and performs efficient flow differentiation. Moreover, the performance improvement is achieved without affecting the useful throughput.