IEEE 802.11e及傳統IEEE 802.11共存之服務品質提升

Abstract

無線網路市場正經歷著爆炸性的成長，由IEEE所制定之802.11標準被廣泛的應用在佈建今日之無線網路。隨著即時應用需求快速成長的同時，在無線網路上提供服務品質變成一個重要的議題。IEEE新制定之802.11e標準旨在提供不同種類的應用程式所需的服務品質區別。雖然IEEE 802.11e能夠提供具有優先順序的媒介存取機制來滿足不同即時應用程式所需的服務品質，但實作802.11e的複雜度以及升級所需的花費將是令目前802.11用戶無法全面汰換現存產品為802.11e之瓶頸。隨著越來越多的802.11e產品的出現，傳統802.11站台與802.11e站台將共存於同一無線網路。在這樣的共存環境中，運行於802.11e站台上之應用程式便可能與運行於802.11上之應用程式進行傳輸，而由於802.11站台缺乏針對服務品質的支援，即時應用所需之端點對端點服務品質將無法被滿足。為了解決這個問題，本文提出一個針對802.11及802.11e之媒介存取擴充，稱為MACAT(具備競爭輔助之媒介存取機制)。在MACAT的規範下，802.11e站台將成為具有即時資料傳輸需求之802.11站台之媒介競爭助理，幫助傳統802.11站台能夠擁有較高的機率取得媒介使用權來傳送即時資料以滿足端點對端點之服務品質需求。我們使用NS-2模擬器來研究MACAT的效能表現，並經由一連串的實驗來顯現MACAT之能力。

The Wireless Local Area Network (WLAN) market is experiencing explosive expansion, and the IEEE 802.11 standard has been widely accepted in deploying WLANs. As realtime applications rapidly grow, providing Quality-of-Service (QoS) to real time traffic over wireless networks becomes important. The newcome IEEE 802.11e standard aims at the supporting of QoS differentiation for various kinds of wireless applications. Although IEEE 802.11e provides prioritized medium access to support QoS for different real-time applications, its implementation complexity and upgrading cost hinder existing 802.11 users from the overall replacement of their legacy nQSTAs and nQAPs. However, it is a promising trend that more and more 802.11e products will be adopted in WLANs, and the legacy 802.11 stations and 802.11e stations will definitely co-exist for a long period. In the co-existence environment, a real-time application executed in an 802.11e station could communicate with the corresponding application in a legacy 802.11 station. In such a case, the end-to-end QoS between the two communicating real-time applications could not be fulfilled. To sovle this problem, this paper proposes an MAC extension, called Medium Access with Contention AssisTance (MACAT), for IEEE 802.11 and 802.11e. With MACAT, IEEE 802.11e stations can act as agents for channel access of legacy 802.11 stations with real-time traffic. Then the legacy stations have a higher probability to acquire the channel for transmitting their real-time data, and the end-to-end QoS requirements can be satisfied. The performance of our MACAT protocol is investigated through the NS-2 simulator, and a series of experiments are conducted to show the capability of our MACAT.