行動式網路下網路層與資料連結層的整合

Abstract

近年來，由於無線通訊技術的發展，使得無線網路與網際網路已結合在一起。這樣的整合環境稱為行動計算環境(mobile computing environment)，而且已成為一種趨勢。在行動計算環境下，行動主機可以隨時移動，並且在移動的過程中繼續保持著資料通訊。雖然行動計算環境提供了較傳統網路更多新的資料服務型態，卻必須提供行動性管理(mobility management)，才能順利完成通訊。 交遞(handoff)對於行動計算環境而言是不可或缺的。行動主機由一子網路(subnet)進入另一個子網路時，會進行交遞的程序。交遞程序牽涉到資料連結層與網路層設定的改變。在這段過程中，行動主機與網路間會中斷一段時間，若此時有資料封包傳送給行動主機，則會造成資料封包的遺失，因而降低上層協定(如TCP)的傳輸效能。 以Route Optimization in Mobile IP為基礎，我們提出一個整合行動式網路下網路層與資料連結層的方法，提供平順的交遞程序(smooth handoff)。根據我們實驗的結果，這個方法確實能減少因交遞所造成資料封包的遺失，改善網路的傳輸效能。

In recent years, due to technology development of wireless communication, wireless networks are integrated with the Internet. Such an integrated environment is called a mobile computing environment, which has become a trend. In mobile computing environments, network nodes are mobile. Each host would move everywhere and still retain connectivity to Internet. Mobile computing environment provides users a lot of new services, but host mobility incurs problems, such as location tracking. Thus, Mobile IP is designed to support host mobility. Handoff procedure is necessary for the mobile computing environments. When a mobile host moves from one subnetwork to another subnetwork, handoff procedure will start. The mobile host will be disconnected from the system for a period during which the host cannot receive data packets from the system. Since the system cannot be aware of this disconnection, data packets sent to the mobile host will be lost. This will degrade the network transmission efficiency. Based on Route Optimization in Mobile IP, we integrate the network and data link layers for mobile networking, and propose a mechanism to support smooth handoff. Using this method, packets loss during handoff procedure will be reduced considerably. By our experiment results, this method is shown to be promising.