在通訊傳輸與無線網路發展蓬勃的現代化社會，各家網路服務的業者(ISP)相繼著手於無線與通訊網路的整合應用，以期提供消費者更多元的網路服務，創造更高的核心價值。而在眾多的網路環境中，使用者該如何來選擇網路路徑來達到較佳的效能，則成為一項網路傳輸中相當重要的課題。 本篇論文為立基於異質無線網路中與802.21MIH共存的網路選擇演算法。本研究所討論的方法是以用戶端的應用程式為導向，針對不同的應用程式，設立不同的參數強度，以參數強度為依據選擇換手路徑，計算出最佳的使用效能，以求獲得更高的服務品質；如使用FTP下載軟體的人會對頻寬有較高的要求，而使用VoIP通話的使用者則會希望通話品質有較高的水準等等。 在本篇論文中共定義了三種主要的網路選擇方程式，並對三個方程式分別做出效能品質及電力消耗的模擬，並在模擬中加入衰弱臨界值(threshold)的判斷因素以求最佳的換手時間點，在換手次數與效能之中取得最佳平衡。在網路選擇的方程式中我們提出六個主要的參數以供判斷，在各種不同的網路中如WiFi，WiMAX等異質網路，以六個主要的參數判斷何者為最適合目前應用程式之網路。本論文提出之演算法是以結合IEEE 802.21 MIH為主，未來將結合動態調整的緩衝機制，以求在網路環境中達無縫之換手之成效。 Media Independent Handover (MIH) is a standard being developed by IEEE 802.21 to enable the handover of IP sessions from one layer access technology to another, to achieve mobility of end user devices. However, how to select an appropriate wireless network which can provide user a high performance service is still an open issue for the MIH. We have discussed a network selection algorithm based on IEEE 802.21 MIH functions in this paper. The algorithm we proposed is used to select the most appropriate network for the applications user is using. For different applications, we made different weights to select different networks to achieve a higher performance or to maintain a higher network quality. In this paper, we defined three main equations to select the most appropriate network. Also we have added threshold values to each application to reduce handover times. In the network selection equation, we have proposed six main parameters to decide which and when should the handover decision be made. The details of the comparison between the algorithm we proposed and the existing algorithm will be shown in the fourth part in this paper. In the future we will add a dynamic-adjusting buffer management mechanism to achieve seamless handover.
