IEEE 802.11aa群播網路回饋機制之設計與實驗

Abstract

近年來隨著無線區域網路的蓬勃發展，消費者們得以使用各式的手持裝置使用多種便利的服務。各家服務提供商也藉著密集布置的無線網路提供豐富的影音多媒體內容。目前為止，這些服務或者影音內容只能透過單點傳播的方式從基地台將封包傳輸給需要的使用者，如此一來將大大地限制可使用的服務種類及品質且會造成不必要的資源浪費。如果在同一個區域底下的數名使用者需要相同或者類似的封包內容時，將封包以群播的方式同時傳輸給所有的使用者將可以大幅地節省使用的無線網路資源並可以提高服務的品質。但在現今的IEEE 802.11無線區域網路標準中，並不支援群播網路的傳輸也缺少多個使用者回報的機制，因此服務商無法提供這一類的群播服務給消費者。IEEE 802.11aa工作小組也因為前述的理由正致力於設計基本的無線區域網路群播機制。在本篇論文中，我們根據IEEE 802.11aa標準目前的機制設計了數種不同的群播回饋機制，並將這些機制與基本的機制相互比較。我們並透過了Linux下的實驗平台，實現了各個不同的回饋機制且加以測試。從結果中我們可以得知我們設計出的回饋機制有較好的效率且可以套用在合適的群播應用中。

In recent years, with the rapid development of wireless local networks, we are allowed to enjoy various convenient services with different handset device. Service providers such as telecommunication companies purvey diverse multimedia contents. Up to now, these contents were mainly transmitted to terminal user via unicast transmission which highly constrain the service types and reduce the network efficiency. Identical content needed by multiple users in local area can be sent simultaneously with multicast transmission and utilize the wireless channel better. However, due to lack of multicast support and feedback mechanism in current IEEE 802.11 networks, those services are impossible to be implemented. Therefore, IEEE 802.11aa task group is now engaged in basic multicast protocol. In this thesis, we implement different feedback mechanisms based on IEEE 802.11aa draft and compare their efficiency to baseline mechanism in the draft. Moreover, we realize a Linux-based testbed with modified wireless WLAN card driver and evaluate all mechanisms above by experiment in real life environment. We also show our design's performance is better than baseline mechanism and can be well apply to real applications.