6.1 結論
在車載無線網路的安全性相關的應用中，主要是藉由散播警告訊息的方式通知駕駛或車輛，
關於道路上的危險事件，藉以避免另發另一起意外事故發生的可能性，確保駕駛及財產的安全。
因此，警告訊息必須要能夠即時的散播且毫無延遲的散播到可能受到影響的區域中，否則將會 增加另一起意外事故發生的可能性。因此，警告訊息的傳輸延遲時間必須在一個可容忍的範圍 內。另外，散播過量的警告訊息，可能導致廣播風暴的問題發生，所以降低警告訊息的數量也 是一個重要的議題。基於這個理由，我們提出了 Fault-Tolerant Broadcast Protocol、Farthest Node First Protocol 及 Exponential Back-off Method，我們所提出的方法不僅能夠減少 alert message 的 傳輸延遲時間，也能夠降低 alert message 的多餘廣播，並且提高警告訊息系統的可靠度。
最後，我們透過 NS2 模擬軟體，並於 NS2 模擬軟體中實作出 FTBP、FNFP、ACK-based Broadcast Protocol 及 flooding method，並模擬比較我們所提出的 FTBP 及 FNFP 與 ACK-based Broadcast Protocol 及 flooding method 之間的效能差異。模擬的結果顯示，我們所提出的 FTBP、
FNFP 及 Exponential Back-off Method 能夠有效的降低警告訊息的數量、訊息的總數量及警告 訊息的傳輸延遲時間。且在節點密度較高的情況下，我們能夠有效的降低 alert message 的數量，
藉以減少 alert message 多餘廣播的問題，降低廣播風暴發生的可能性。此外，模擬的結果也顯 示出 FNFP 能夠有效的降低警告訊息的傳輸延遲時間，給予駕駛更多的反應時間。
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6.2 未來工作
在 NS2 實驗模擬中，由於我們所撰寫的 Fault-Tolerant Broadcast Protocol 及 Farthest Node First Protocol 的程式，並不適合直接在市區道路(manhattan model)場景中模擬實驗。主要的原 因是，在我們的程式中，主要是針對高速公路場景所撰寫的，來源車輛在挑選 relay vehicle 時，
能確實讓 relay vehicle 向公路後方延伸。但在市區道路場景中，來源車輛只能讓 relay vehicle 向市區道路後方延伸，並不能直接讓 relay vehicle 向市區道路的左邊及右邊延伸。針對這個問 題，我們希望往後能藉由修改並擴充 FTBP 及 FNFP 的程式，讓 FTBP 及 FNFP 的封包資料結 構中，新增挑選左邊及右邊方向的 relay vehicle 資料欄位，讓 FTBP 及 FNFP 在市區道路場景 中，不僅能夠向市區道路的後方挑選 relay vehicle，也能夠在市區的左邊及右邊道路上挑選 relay vehicle。讓我們能夠在市區道路中模擬實驗，來取得市區道路的數據資料
此外，在我們所提出的 FTBP 與 FNFP 中，我們所挑選的 relay vehicle 都是挑選在危險車 輛後方且與危險車輛相同車道的車輛，若是危險車輛後方並沒有車輛行駛時，可能導致危險車 輛挑選不到 relay vehicle 的情況，造成警告訊息傳遞中斷。我們希望未來能夠藉由挑選在危險 車輛反向車道的車輛當作 relay vehicle；當危險車輛後方並無車輛行駛時，改由挑選危險車輛 對向車道的車輛當作 relay vehicle，來避免警告訊息傳遞中斷的問題。
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