我们介紹一個新的分析模型來探討IEEE 802.11E STANDARD之中加強型分散式協調功能(EDCF)的性能表現。加強型分散式協調功能被模型化成馬可夫鏈，其包含了AIFS(任意訊框間隔)、最小遞後存取視窗大小、重傳限制、遞後存取的凍結機制以及不同的封包大小。基於提出的模型，我们推導出不同優先權等級的飽和傳輸率與飽和延遲。不同的參數如AIFS和封包大小對加強型分散式協調功能差別服務的影響被分析式地展示出來。

　　IEEE 802.11E EDCF著重於支援MAC層的相對性差別服務。然而，遞後存取機制可能導致嚴重的封包延遲和抖動。為了保證對聲音與影像串流的服務品質，我们對IEEE 802.11E加強型分散式協調功能提出一個針對資料的服務品質控制技巧融合一個以測量為基礎的允入控制機制。在提出的允入控制技術中，存取點根據個別即時訊源的要求保留頻寬，同時針對資料的服務品質控制技巧係基於IEEE 802.11E EDCA 參數的動態調整。所提機制的性能表現藉由模擬被廣泛地探討。模擬結果顯示：使用提出的針對資料的服務品質控制與允入控制機制，即時多媒體訊務獲得極好的服務品質，並且能全面利用通道容量。

　　We investigate the performance of the emerging IEEE 802.11e standard by introducing a novel analytical model for the enhanced distributed coordination function (EDCF). The EDCF is modeled as a Markov chain which encapsulates AIFS (arbitrary inter-frame spacing), the minimum backoff window size, retry limit, freezing mechanism in backoff, different packet size. Saturation throughputs and saturation delays of different priority classes are derived based on the proposed model. The influences of different parameters like AIFS and packet size on the EDCF service differential schemes are demonstrated analytically.

　　IEEE 802.11e EDCF aims at supporting relative service differentiation in the MAC layer. However, the backoff mechanism may cause huge packet delay and jitter. In order to guarantee quality of service for voice and video flows, we propose an ABR-QoS control scheme integrated with a measurement-based admission control scheme for the IEEE 802.11e enhanced distributed channel access. In the proposed admission control strategy, the access point makes bandwidth reservations according to individual real-time source’s requirement, while the ABR-QoS control mechanism based on a dynamic adjustment of the IEEE 802.11e EDCA parameters. The performances of the proposed scheme are extensively investigated by simulations. Simulation results show that, with the proposed ABR-QoS control and the admission control scheme, real-time multimedia traffic obtains great quality of service while the channel capacity is fully ultilized.

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