一個改進無線網路服務品質之代理人機制

Abstract

中文摘要 隨著無線網路的進步與普及化，筆記型電腦或任何手持式裝置（PDA、Smart Phone）只要加裝無線網路卡或內建無線晶片，即可隨時隨地連接上網。一般而言，當使用者進入無線網路的涵蓋範圍後，無線網路卡（無線晶片）便會搜尋離它最近且訊號最強的基地台來做連結；可是這並不保證訊號強，使用者就可以享有較佳的通訊品質，主要的原因是沒有考慮到該基地台下面有多少使用者及可用的頻寬，一旦使用者越多，那麼每個使用者所能使用的頻寬也就越少，通訊品質也因此下降。 在本篇論文中，我們提出了一個預警式代理人協助（Anticipative Agent Assistance；AAA）的機制，該機制主要是管理整體無線基地台的資訊，並經由我們的演算法計算出最佳的基地台列表，最後由AAA以預警的方式知會使用者在他附近有哪些可提供較好服務品質的基地台。另外，我們還提供了服務品質回饋（QoS feedback）的觀念，根據事前所協定好的傳輸速率（throughput）、延遲（delay），讓使用者在傳輸過程中，透過與AAA的互動來達成即時調整服務品質的目的。 在效能評比方面，我們透過網路模擬程式（ns-2）來驗證我們所提出的機制與架構，模擬的結果確實能達成我們預期的目標：減少延遲（transmission delay）、提高傳輸速率（throughput）、提升整體網路的使用率（utilization）、提高使用人數（users）及提供負載平衡的功能（load-balancing）。

Abstract With the development and popularity of wireless networks, people can easily access the wireless Internet using notebook PCs or handheld devices (PDA and Smart Phone) equipped with wireless cards or build-in chips. Generally, wireless cards (wireless chips) will try to associate with the nearest access point (AP) which usually has the strongest signal. However, this does not guarantee that users will have better quality of communication service. The main reason for this is not considering the number of attached users and available bandwidth at each access point. Thus, the more the number of users is, the less bandwidth each user can get, and the worse the communication quality will be. We proposed an Anticipative Agent Assistance (AAA) mechanism for wireless networks in this thesis. AAA is mainly in charge of managing the control information of the entire wireless access points, computing the potential AP list with our proposed algorithm, and then ahead informing the users of AP with better service. Moreover, we also applied the novel idea, QoS feedback, which allows users to promptly adjust the service quality with AAA according to throughput and delay requirements. We evaluate the performance of our proposed method using the ns-2 simulator, and the results show that AAA achieves: (1) to reduce the transmission delay, (2) to increase the throughput, (3) to improve the network utilization, (4) to accommodate more users to access the network, and (5) to provide load-balancing mechanism.