模擬結果

5.4.1 整體換手延遲時間分析

圖 5.4 為整體換手延遲時間的分析圖，No_MIH_support 表示沒有支援媒介 獨立換手機制的換手，MIH_support 表示具有支援媒介獨立換手機制的換手。根 據實驗結果顯示，在 WiMAX 同質網路下的換手，沒有支援媒介獨立換手機制的

WiMAX‐>WiMAX Wi‐Fi‐>Wi‐Fi Wi‐Fi‐>WiMAX WiMAX‐>Wi‐Fi

時間(秒)

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WiMAX‐>WiMAX Wi‐Fi‐>Wi‐Fi Wi‐Fi‐>WiMAX WiMAX‐>Wi‐Fi

時間(秒) 手延遲時間，在 Wi-Fi (WiMAX)換手到 WiMAX (Wi-Fi)為 0.633 (0.101)秒，較沒 有支援媒介獨立換手機制以及有支援媒介獨立換手機制所花費的時間少，這是因 為快速連結網路方法藉由 MIH Get Information 訊息來幫助行動節點取得鄰近周 圍的網路資訊，進而縮短進入新的網路延遲時間，因此可知 MIH Get Information 訊息的確可以改善異質網路下的換手延遲。

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Wi‐Fi‐>WiMAX WiMAX‐>Wi‐Fi

時間（秒） No_MIH_support

MIH_support

換手方法 WiMAX->WiMAX Wi-Fi->Wi-Fi Wi-Fi->WiMAX WiMAX->Wi-Fi

No_MIH_support 0.792% 0.602% 1.442% 0.793%

MIH_support 0.258% 0.474% 0.233% 0%

Fast_association 0.029% 0%

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第六章 結論

本論文根據 IEEE 802.21 草稿中提出的媒介獨立換手機制，我們討論在同質 性網路和異質性網路下的換手程序，並加入媒介獨立換手機制的支援，來改善換 手的延遲時間，透過即將離線事件預先偵測即將斷線的可能性，提早開始換手流 程，我們也提出增加 MIH Get Information 訊息的支援，讓異質性網路上的垂直 換手，可以更快速建立新網路的連線。

透過 NS2 模擬的結果驗證出，媒介獨立換手機制的支援明顯地降低換手延 遲的時間，並且能夠降低封包的遺失率，藉由媒介獨立換手機制的支援，幫助協 調、管理不同介面的運作。在 WiMAX 網路切換到 Wi-Fi 網路上的換手實驗結果 顯示沒有封包的遺失，所以幾乎達到無接縫的換手。

未來，在 IEEE 802.21 的標準制訂完成後，還可以將其他不同網路媒介一起 加入討論，相信對於行動節點在各種不同網路環境中的換手研究必會有所助益。

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