隨著無線網路環境的普及，越來越多行動工作者可以透過隨身的手持設備進行網路漫遊，即時地存取不同的服務。另外亦可以經由公司的虛擬專有網路來存取企業內部資料、電子郵件及其它應用程式。不論是針對企業或是網路服務業者而言，為了要能夠確保網路環境上的安全性，眾多的行動工作者在進行漫遊時，身分必須被驗證，進而才能被授予各項服務的存取權。此外，還必需根據使用者服務使用的情況進行計費，來提升服務提供者的收益。
因此在無線區域網路中，結合一套認證、授權、計費的架構(Authentication, Authorization, Accounting Architecture, AAA
Architecture)，使得網路服務業者能夠有效地來管理龐大行動工作者的跨網路漫遊服務。

本研究提出一個以情境知覺運算(context-aware computing)為基礎的AAA架構。以情境來設計資源存取政策，因此系統偵測到行動工作者情境上的改變，根據已定義好的存取政策，動態地進行身分驗證及調整授權服務，最後再依不同的服務使用等級、連線時間與網路使用量等來計費。本論文以漫遊服務與企業虛擬專有網路為例，說明在此架構下如何針對不同的情境進行身分認證、與服務授權。

With the popularity of the Wireless LAN, mobile workers are able to access various services or resources with seamless roaming, as well as mobile VPN, just via their handheld devices. Not only for the corporations but the Internet Service Providers(ISP), a secure and trusted remote access is required. User identity should be authenticated in advance, and the service providers grant or deny mobile users the access to resources according to their statuses.
Besides, a usage-based accounting and billing is crucial to provide commercialized services within WLAN, and to benefit those service providers. As a result, a AAA architecture designed for coordinating the authentication, authorization and accounting between different administrative networks is required with urgent need.

The objective of this research is to provide a context-aware based AAA architecture which adopts context as the design principle to define access control policies. So the system can detect the changing contexts of mobile workers, re-authenticate user identity, adjust dynamically service permissions in the light of context-based access control policies, and bill the user taking into account the contexts efficiently. In this research, we take examples of roaming services and VPN to describe how the architecture works.

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