Ieee 802.11e In The Txop And Access Control Mechanisms Of The Research And Improvement

As people's living standards, facilitation of the network access requirements are getting higher. More and more people began to use WLAN. It also means that the quality of service for wireless services has to set higher requirements. People use WLAN not limited to best effort services, but extended to multimedia applications.The IEEE 802.11 is the most popular criteria in WLAN. However, original 802.11 MAC protocol can't support QoS differentiation. 2005, IEEE 802 Task Group defines a new standard for MAC QoS enhancement which is called IEEE 802.11e. 802.11 defines two different access mechanisms: EDCA (Enhanced Distributed Channel Access and HCCA (HCF Control Channel Access). In this paper, we focuses on the EDCA. We address the issue of TXOP Limit and admission control, which is part of QoS enhancement in EDCA.EDCA can differentiate different AC through defining for each ACs a specific parameter set. But the different flows belonging to the same AC have the same parameter set, it means that EDCA can not have a intra-AC QoS differentiation. And EDCA does not have a effective admission control mechanism to protect QoS of the flows being admitted. In this paper, we proposed a new algorithm computes TXOP Limit by monitoring the MAC's AC queues. When a AC acquires the medium, it gets the send rate and the length of packet in the AC buffer queue. Every flow will have a different TXOP Limit based on instantaneous queue length, and it could provide an intra-AC differentiation.A new arrival flow will increase the collision rate in the network and degrade the active flows'QoS. In the paper, we design a admission control mechanism based on the collision of the AC flow. When collision rate is higher than a threshold, flows is not admitted to access to the medium. It can protect QoS of the exist flows. The simulation results show that the admission control mechanism ensures throughput and delay to the exit flows while maintaining high network utilization.