移動網路中合作模式的換手管理

Abstract

對現今許多的網路服務提供者來說，因為多種無線網路技術的發展，在移動漫遊的環境中同時提供WiMAX、HSDPA與Wi-Fi等異質無線存取技術，讓使用者可以依據當時使用環境與應用程式頻寬上的需要，選擇不同種類的無線網路連接網際網路，這一直是網路服務提供者的遠景。在本篇論文中，我們提出了在無線網路漫遊的情境中，設計了讓許多網路服務提供者在合作模式中(cooperative)同時可以達到快速安全認證的漫遊方法與一個由使用者自己依據成本與頻寬的考量，自行決定的服務等級的方法。在無線服務提供者之間所形成的合作模式下，這些不同的無線網路技術將被整合為一個完整的資源。 要達到上述的無線漫遊網路服務目標，有四個重要的議題要在本論文探討:1)行動使用者使用IP之定址方式，在無線網路中移動的同時，也需要使用漫遊服務，而不受限於其無線網路服務提供者的服務區域；2)在缺乏互信的情況下，使用者與每個無線網路服務提供者之間、以及每個無線網路服務提供者之間必須建立彼此互相信任的關係，其中包含了計費、認證機制與無線資源分享；3)在漫遊時因為認證機制或者無線網路訊息交換所增加的漫遊時間，必須加以縮短，因為時間延遲對如網路電話或者串流服務的品質影響甚鉅；4)在有多個不同網路技術服務選擇下，在成本與頻寬的考量之下，使用者如何選擇其需要的無線網路技術。 在本論文中，針對計費、認證機制我們設計了讓使用者攜帶的U-Mobile Token，此Token在合作模式下之不同無線網路服務提供者之間被認證，可以大幅縮短漫遊時因為認證、計費所造成的延遲。在此問題上我們也設計與實作【Fast and Secure Universal Roaming System】縮寫為FAS-URS (唸作Fas(t) Earth)系統，此系統證實了漫遊者在不同的無線網路服務提供者之間可以享受快速且不中斷的通訊服務。 在使用者的服務品質的議題上，目前無線網路服務提供者普遍使用單一定價(Flat-rate)，雖然使用者可以無限制使用網路資源，但是實際上卻無法保證網路服務品質 (Quality of Service)，我們也在異質無線服務業者的合作模式(例如WiMAX與 HSDPA)的環境下，提供使用者多個選項，使用者可以依據其所付出的成本與需要的服務等級，選擇最適合的無線網路服務。在我們的模擬中，其結果顯示，此架構同時提高了使用者的滿意度，也讓無線網路系統可以容納更多的使用者，創造更高的利益。在本論文中，我們延伸此服務模式至垂直換手服務，在垂直換手的情境中，除了可以達到無縫式換手之外，我們仍可保證其在原網路中之服務等級。

Employing multiple radio access technologies such as WiMAX, HSDPA and Wi-Fi in a mobile network to provide users with more cost-effective communication services has long been a vision of many service network providers. In this thesis, we propose a security roaming solution in handover scenario and provide a novel user-decided service model in a cooperative wireless network environment and in the last, we based on user-decided service model, proposed a QoS guaranteed solution in vertical handoff scenario. When the radio resources of multiple wireless networks are collectively managed, four issues are raised in such a communication environment: a) service users would like to have IP-based roaming capability as they move rather than being constrained to a single spot or being forced to disconnect because his/her service provider does not have entire coverage of the city/region; b) the need on security and accounting management for mobile Internet; and c) the execution of AAA however would incur extra delay to handoff latency. For applications like VoIP, video streaming and TCP connections, it may disrupt the on-going communications if such latency becomes too large. d) within these versatile reless technologies, how can mobile users choose the suitable wireless network to move in. In this work, we propose an AAA-enabled roaming alliance architecture that provides fast and secure universal roaming service across multiple service domains. The associated protocols and the supporting security mechanisms are also proposed. Our design provides continuing communications service to mobile user belonging to different service operators to quickly and securely access service when roaming across multiple service domains. Mobile users only need to carry a U-Mobile Token to receive the service. The schemes proposed only incur minimal latency in security check. This is particularly important to the support of real-time mobile applications. For the novel user-decided service model which provided with multiple service options with different levels of service quality and charges. It is up to users to choose the most suitable service option (and access network) based on their personal preference and the amount of money they are willing to pay. We use a video streaming service in a WiMAX/HSDPA network as an example to illustrate the key concepts and resource management of our approach. The results of simulation show that, under the model, the service network can accommodate more users and provide higher user satisfaction than the traditional network-decided service model. It can also achieve higher resource utilization and revenues. We also extend this service model to vertical handoff service, besides providing seamless handoff, also keep the QoS service level as in the original network.