Study, Based On The Ieee802.11e Dynamic Txop And Access Control Algorithm

The personal data communication is more and more tend to wireless. Multimedia services such as video and audio extend to the wireless mobile communication and have gradually been the main trends of the future development of wireless communication systems. How to provide multimedia services to ensure quality of service becomes the research hotspot. Improve the performance of MAC protocol is an effective approach to provide quality of service guarantees of multimedia services.IEEE 802.11 is the main standard in wireless local area networks. 802.11e is proposed to support QoS of multimedia services. With the trendency of increasing applications and growing network scale, it is critical to improve the performance of 802.11e for providing QoS guarantee. This thesis studies the QoS guarantees and admission control mechanism in 802.11e based wireless networks.CFB Mechanism can increase the network utilization and throughput, reduce latency and packet loss rate, but CFB Mechanism still has defects: CFB can't provide QoS guarantees based on traffic flow to the flow of different datarate which belongs to different priority, and CFB can't meet the fairness.Because the essential cause of the CFB Mechanism is the fixed TXOPLimit value. Due to the existent defect of CFB Mechanism, this thesis proposes the DTXOP algorithm. According to the instantaneous network state, we differentiate different AC and different flows which belong to the same AC through dynamic TXOP service difference, guarantee the fairness of throughput of high priority. The simulation validates that DTXOP algorithm shows its advantage when the network load is high. The new algorithm solves the disadvantage of CFB Mechanism, guarantees the QoS requirement of different AC and different flows which belong to the same AC. However, the improved performance of high priority is based on sacrificing the performance of low priority, so it is necessary to provide an admission control mechanism to protect QoS of flows being served.The EDCA mechanism only provides differentiated service, it falls short in ensuring sustained QoS guarantees by developing some sort of admission control mechanism. It is impossible to control network flow and guarantee QoS. Based on the DTXOP algorithm, the thesis proposes a fully distributed admission control algorithm that regulates the network load to protect the already admitted flows from new entering flows. The simulation results show that the admission control mechanism ensures high protection to the admitted flows while maintaining high network utilization.