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題 名 | 無線區域網路媒介存取協定研究與效能分析=Performance Analysis of an Improved Medium Access Protocol for Wireless Local Area Networks |
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作 者 | 江松茶; 張朝欽; | 書刊名 | 技術學刊 |
卷 期 | 14:2 1999.06[民88.06] |
頁 次 | 頁279-287 |
分類號 | 448.6 |
關鍵詞 | 無線區域網路; 分散式協調功能; 隨機後退程序; 吞吐率; WLAN; DCF; Random backoff procedure; Throughput; |
語 文 | 中文(Chinese) |
中文摘要 | IEEE8 802.11協定使用的媒介存取控制是一種分散式控制模式稱為分散式協調功 能 (DCF),主要使用隨機後退程序作為媒介存取的協定。在此協定下,當存取的需求增加時 ,因封包碰撞而存取失敗的機率亦隨之增加,嚴重的話可能造成系統不穩定。本篇論文首先 對 802.11 協定的效能作模擬分析並研究其缺點及限制,然後我們提出了可改善並適應各種 網路條件的預約存取模式。此模式將媒介的存取劃分競爭區間及免競爭區間兩部份,在競爭 區間仍然沿用隨機後退程序,作為工作站預約存取之用,在免競爭區間工作站監聽媒介並按 存取的先後次序輪流使用。經過我們模擬分析的結果發現預約存取模式的效能比原協定提高 了,尤其是負載較重時有明顯的改善效果。除了效能比原協定提高外,加上預約存取模式尚 具有 IEEE 802.11 分散式協定所無法提供之時限性服務及優先權服務的能力, 可提供語音 的即時需求和影像資料的高優先權需求,對多媒體應用有正面助益。 |
英文摘要 | The medium access control in the IEEE 802.11 standard is a distributed protocol called Distributed Coordination Function (DCF). The DCF employs the random backoff procedure. This method may become unstable when traffic generated at each user increases rapidly due to access conflict. This paper first simulates the performance of the DCF protocol and studies its drawbacks and limitations, then proposes a new method to improve the situation, and which can adapt to various network conditions. Our method, called DCF- reservation, divides the medium access into a contention period and a contention free period. During the contention period, we still utilize the random backoff procedure, allowing the workstations to make reservations, while during the contention free period, the workstations will monitor the channel and access the medium according to the priority access schedule. Simulation results show that our DCF-reservation scheme outperforms the original protocol. The improvement is especially obvious in heavy traffic load situations. Furthermore, our protocol is able to support time bound services and priority services that the 802.11 MAC layer has difficulty providing. Under our proposed protocol, one can provide multimedia applications because the protocol is able to satisfy the need of high priority of real-time voice and the requirement of data and imagery. |
本系統中英文摘要資訊取自各篇刊載內容。