一個在Wi-Fi下基於串流行為之服務品質改良機制

Abstract

隨著時間敏感性的服務在網路上越來越多，服務品質現今成了網路工程領域內的一大議題，也就是說，要如何將具有較高優先權的網路封包先行傳送是一個急需但尚未解決的問題。因為對於服務品質的需要，電機電子工程師學會 (IEEE)對無線網路的環境提出了支援服務品質的規格802.11e，該規格藉由修改MAC層改進了原有802.11對於服務品質規格的不足。然而，因為規格內並沒有明確的規範整個架構，並且因為服務品質在實作上的困難，導致現在還沒有什麼具有服務品質的機制被實作並真正被廣泛使用。 基於以上的原因，在本篇論文中我們提出了一個新穎的機制使得在一無線基地台下可以支援服務品質的服務，該機制會先觀察每條經過基地台的資料流並進行紀錄，並在短時間內依照所獲得的資料將資料流分類並給該資料流相對應的優先權值，之後基地台就會將該資料流的封包導進對應的封包佇列。該機制主要是依據封包大小的分佈及封包與封包之間相隔的最大時間作為分類的依據。在最後的模擬結果中，我們可以發現當基地台利用我們的機制時，該基地台可以大幅改進資料串流的服務品質。

QoS becomes one of the most important issues in networking nowadays because of the growth of time-sensitive services. In other words, how to transmit the packets with higher priority first is a big issue need to be addressed in recent years. IEEE 802.11e was proposed and it defined a set of QoS enhancements for wireless local area network (WLAN) applications through modifications to the media access control (MAC) layer due to the imperfection of QoS in the legacy 802.11 MAC. However, because of the indefinite specification and the difficulty in implementation, the QoS mechanism has not been implemented in the real world. In this thesis, we propose a novel mechanism for QoS support of WLAN. The proposed mechanism detects the behavior of each traffic flow passing through the AP, and classifies the traffic flow with a proper priority. The packets would be assigned to the proper access category eventually. The classification is based on two features, the packet length distribution and the maximum packet inter-arrival time. As the simulation results showed, the proposed mechanism can enhance QoS of WiFi remarkably.