在犯罪率居高不下的社會中，合法監聽常被用來取得犯罪者的通訊，以得知其下一步的行動。以往都是藉由傳統電話的監聽來破案，但隨著網際網路的普及，網路電話以及視訊會議也被廣泛使用，因此針對網路監聽的研究便成為一大重要的議題。常見的網路電話通訊協定包含 H.323 和 SIP，H.323 的架構非常完整，在監聽方面僅需在通訊的路徑上建立監聽的機制即可達成；然而 SIP 僅負責通訊的建立，通訊封包的傳輸路徑並無特定的規範，此協定的擴充性雖然高，但在監聽的議題上便相當困難，尤其是運作在移動式網路時，其通訊的路徑更難掌握，以及移動式的資訊也將難以取得。 本論文針對移動式網路之 SIP 服務提出三種監聽的策略，Centralized Wiretap-Agent-based Interception Strategy (CWAIS)、Distributed Wiretap-Agent- based Interception Strategy (DWAIS) 和 Home-Agent-based Interception Strategy (HAIS)，並分析及比較各種策略之優缺點。本論文選擇以HAIS來實作，其主要原因在於此策略可運作於現行的網路，且在監聽的過程中，使用者無法察覺自己已被監聽。最後以各種參數針對此系統設計出實驗，以驗證系統運作的可行性，並分析各項實驗的結果。 With the high crime rate society, lawful interception is used to get the communication of the offenders. Interception of the traditional telephone is used to solve the criminal cases before. But following to the popularization of the Internet, people uses Voice over Internet Protocol (VoIP) and video conference to communicate with each other generally. Thus, the research of the interception with the network will be an important subject. The common protocols of VoIP include H.323 and SIP. H.323 has the complete structure. Interception of H.323 is just established the wiretap mechanism on the path of the communication. However, SIP rules the establishment of the connection only, the path of the transmission is not defined. Therefore, It is hard to intercept the media streams. Especially, when SIP is operated with mobile IP, It is hard to be aware the path of the communication and get the mobile information. In this paper, three SIP wiretap strategies with mobile IP are proposed, including Centralized Wiretap-Agent-based Interception Strategy (CWAIS), Distributed Wiretap-Agent- based Interception Strategy (DWAIS) and Home-Agent- based Interception Strategy (HAIS). Each advantage and disadvantage of these strategies will be analyzed and compared. In this paper, HAIS is chosen to be implemented. That is because it can be operated with current network. And the SIP clients can not be aware that they are intercepted. Finally, the experiments are designed for this system with several parameters. The feasibility can be verified and the experimental results are analyzed.
