無線區域網路上具品質保證之傳輸服務

Quality of Service Guarantees in IEEE 802.11 Wireless LANs

鄧德雋(Der-Jiunn Deng)

指導教授 ： 顏嗣鈞

國立臺灣大學/電機資訊學院/電機工程學研究所/博士(2005年)

https://doi.org/10.6342/NTU.2005.00333

摘要

隨著通訊技術的發展，無線網路已成為電腦網路中日趨重要的研究領域，但是，大部份無線網路的媒體存取控制協定卻因缺乏優先等級或一套完整的存取控制策略而無法支援未來傳輸多媒體資訊的需求，在本文中，我們提出優先權的概念來支援多媒體資訊的傳輸，並分別為兩種不同的無線網路設計一套以優先等級為基礎的無線網路存取控制機制。

關鍵字

品質保證 ； 無線區域網路

並列摘要

In wireless local area networks (WLANs), the medium access control (MAC) layer protocol is the main element that determines the efficiency of sharing the limited and unreliable communication bandwidth of the wireless channel. IEEE 802.11, the standard of Wireless Local Area Networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the Distributed Coordination Function (DCF) and Point Coordination Function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic as well as user mobility. Besides, the backoff parameters of its collision avoidance mechanism are hard-wired in the physical layer, and are far from the optimal setting in some network configuration conditions especially in heavy load or error-prone WLAN environments. To expand support for applications with Quality-of-Service (QoS) requirements, the 802.11E Task Group was formed to enhance the original IEEE 802.11 Medium Access Control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks is still remain unsolved. In this dissertation, we propose a polling with non-preemptive priority based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff call can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLANs environment, and can be easily incorporated into the Hybrid Coordination Function (HCF) access scheme in the IEEE 802.11e standard.

並列關鍵字

QoS ； 802.11 ； WLAN

參考文獻

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