一種在異質網路中對於垂直無縫交遞的聰明決策模組

Abstract

近年來，如WLAN、GPRS、3G等的網路技術越來越普及。這些網路的信號範圍彼此互相覆蓋的機率相當高。對於漫遊在這些網路之間的用戶而言，他們希望不管漫遊到哪個網路中，都能夠隨時隨地連接上線。因此，垂直無縫交遞成為一個重要的問題。 為實現高性能，使用者會希望能選擇最好的網路來連接。 然而，如信號複蓋範圍，最大資料傳輸率，價格，耗電量等特性，在不同的網路之間，會有很大的差異。此外，各種不同類型的服務，需要這些特性的不同組合。 雖然大多數對於垂直交遞是基於單一政策來優化服務，並未考慮不同服務間的差異。因此，我們提出了一個以服務差異為主的交遞決策模式。通過這樣的決策模式，使用者可以基於所使用服務的不同來調整估價函數中各個參數的比重。因此我們可以更恰當的方式來選擇所要用的網路。 在最近的研究中，大部分都是用mobile-IP來實現垂直交遞。然而，在mobile-IP裡，需要透過自家網路的代理伺服器與外界網路代理伺服器的幫助，才能實現垂直交遞，而這樣的模式會造成代理伺服器負荷過重的情況。而在我們的垂直交遞計畫裡，只需要靠使用者自己的移動裝置，就能實現垂直交遞，因此簡化了整個垂直交遞所需的步驟。此外，我們透過實作讓我們的垂直交遞能在比mobile-IP更短的時間內完成。

In recent years, network technologies such as WLAN, GPRS, and 3G are getting more and more popular. There is high probability that signal coverage of these coexisting networks overlaps with each other. For a user roaming among these networks, it is desirable that his or her mobile device can have anytime connectivity, and therefore vertical handoff becomes an important issue. To achieve high performance, a user may want to choose the best network to connect to. However, properties such as signal coverage area, maximum data rate, monetary cost, and power consumption on end devices vary largely among these networks. Moreover, different types of services require various combinations of these properties. While most vertical handoff schemes are based on single optimization policy in which service difference is not taken into consideration, we propose a service-based handoff decision model. Through this decision model, weight of the parameters in the cost function is adjustable based on the type of service in use, and therefore we can make a more appropriate decision on network selecting. In recent research, mobile IP is a generally used handoff scheme. However, to facilitate vertical handoff, help from a home agent and a foreign agent is required in the mobile IP scheme, which induces overloading on the agents themselves. In our handoff scheme, only with mobile host itself can handoff be realized, hence the overall handoff scheme is simplified. Moreover, through our implementation, handoff latency can probably be even shorter than that in the mobile IP scheme.