無線通訊系統因為其方便性，漸漸的被人們所廣泛的使用。國際電氣和電子工程師協會(IEEE)為區域無線通訊方面所制定的802.11無線區域網路標準在實體層已經可以為資料的傳送提供足夠高的傳輸頻寬了，然而，當初在媒體存取控制 (MAC)層所制定支援的兩種傳輸模式，也就是分散協調式功能(Distributed Coordination Function, DCF)和集中協調式功能(Point Coordination Function, PCF)，卻不足以支援多重服務等級的資料之傳輸。
在這篇論文中，我們將提出一些修改方法和運作機制，讓802.11無線區域網路媒體存取控制通訊協定能根據要被傳送的不同資料之特性而提供不同的服務品質上的保證。我們在這篇論文中採用了全球行動通訊系統(Universal Mobile Telecommunications System, UMTS)所制定的標準，將資料種類分成四個等級：(1) 通話等級(conversational class), (2) 資料流等級(streaming class), (3) 互動型等級(interactive class), (4) 背景執行等級(background class)。我們的連線允入控制(Connection Admission Control)機制和媒體存取排程演算法將為以集中協調式功能為運作基礎的即時性(通話和資料流等級)資料傳輸和以修改過的分散協調式功能為運作基礎的非即時性(互動型和背景執行等級)資料傳輸提供服務品質上的保證，支援多重服務等級的資料之傳輸。

在軟體模擬中，我們發現所提出來的媒體存取控制通訊協定的確能滿足不同資料等級在服務品質上的要求，支援多重服務等級的資料之傳輸。我們把所提出來的方法和其他改進分散協調式功能的方法做比較，發現我們提出的運作機制能有效的隔離較低層級來的干擾，更能分出媒體存取的高低權限。

The IEEE 802.11 wireless Local Area Network (LAN) provides high bandwidth for data transmission in low tier wireless networks. However, the access method of IEEE 802.11 cannot meet the Quality of Service (QoS) requirements for all kinds of traffics. In this paper, we propose some modifications and mechanisms for the IEEE 802.11 Medium Access Control (MAC) protocol to provide the QoS guarantee according to the characteristics of the traffic. We adopt four different traffic classes: namely conversational class, streaming class, interactive class, and background class proposed, by the UMTS [3]. The Connection Admission Control (CAC) and the scheduling algorithm provide the guarantee of the QoS requirements for real-time traffic (conversational and streaming classes) based on the polling in Point Coordination Function (PCF) mode and for non-real-time traffic (interactive and background classes) based on the modified CSMA/CA with different access priorities in the DCF mode.

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