移動式隨意網路(MANET)長期以來一直是無線領域上很重要的一部份，因為它能提供一個便利的無線傳輸環境，然而它的不穩定性、不安全性、不可靠性使得它實用性大幅降低，移動式隨意網路有三大限制，第一：拓樸環境一定是動態的，第二：硬體能力是較差的，第三：無法保證傳輸安全性，換句話說，要提升移動式隨意網路效能就要克服這三大限制，動態的拓樸環境導致傳輸路徑無法維持，因此提升傳輸路徑的穩定性及資料的傳輸成功率是我們的第一個目標，我們根據這狀況提出了一個使用地理資訊及獨特的傳輸機制來改善移動式隨意網路的傳輸效能，到了第二階段，由於受限網路上各裝置的硬體能力，我們將研究環境轉向與移動式隨意網路非常相似的環境『車用隨意網路(VANET) 』，在車用隨意網路，已經大幅改善裝置的硬體能力，所有的裝置大部份是車上裝置(OBU)，然而仍然存在著大量移動式隨意網路就存在的問題，因此我們首先對車用隨意網路進行分析，並根據其特性提出了一個智慧型封包傳輸機制來改善車用隨意網路中時斷時續連線(intermittent connectivity)等問題。最後我們探討無線網路上的安全性問題並以網路電話(VoIP)為主題，網路電話是一個相當成熟的技術，然而當應用在無線的環境中，很多安全性問題一一浮現，我們針對整個網路電話的架構及終端移動(terminal mobility)的特性來改善這些問題。

Mobile ad hoc networks (MANETs) are an important topic in wireless network research, because they provide a convenient communication environment. However, their instability, insecurity, and unreliability make them impractical for data communication. There are three limitations of MANETs: a dynamic topology, insufficient hardware resources, and insecurity. Overcoming these limitations can improve MANET performance. The topology is dynamic in the sense that the link state is unstable and that it is difficult to maintain the transmission path. Thus, our first purpose is to improve stability and data delivery ratio. We propose a specific communication scheme to improve performance using geographic information. In the next step, we focus on a new environment, called vehicular ad hoc network (VANET), which is similar to MANET. In VANET, hardware resources are no longer sufficient, because most of the devices are on-board units (OBU). In general, an OBU has sufficient power, memory, and CPU strength. However, the disadvantages of MANETs (e.g., unstable link) still exist in VANET. Therefore, we analyze the properties of the VANET environment in detail and then propose an intelligent packet-forwarding scheme to improve performance. Finally, we discuss the wireless security issue and focus on VoIP security. VoIP is a convenient technology but has many security issues in wireless networks. Therefore, we propose a secure VoIP system structure for wireless security.

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