Abstract: The IEEE 802.11 standard MAC is a hybrid protocol of random access and polling when both DCF (distributed coordination function) and PCF (point coordination function) are used. This (paper) studies the performance of the MAC protocol for integrated data and voice transmission where data traffic is transmitted with the DCF, and voice transmission is carried out with the PCF. By simulation, we evaluate the network throughput and the average MPDU (MAC protocol data unit) delay for various values of the protocol parameters and determine the maximal number of the voice service users on the condition of defined data throughput. Especially, voice traffic is sensitive to delay jitter and here we point out the main influencing factors. Numerical results show that it is important to choose appropriate protocol (parameters) and we should make a compromise between the number of the voice stations and the data traffic throughput to get the enhanced performance of IEEE 802.11. Finally, the performance of protocol is (derived) theoretically, which verifies the correctness of the simulation results.