在以往使用者採取撥接上網，或網路頻寬較小的時代，多媒體服務會因為頻寬的限制，無法達到使用者能滿意的品質，但因為網路的技術越來越成熟，頻寬的加大，網路的普及性，讓多媒體的服務也漸漸的受到大家的注目，也越來越多人開始使用多媒體的服務，例如網路電話 (Voice over IP，簡稱VoIP) 及視訊會議 (Video Conference) 等，這些服務目前又以VoIP最廣為使用。在各種VoIP技術中目前最廣為使用的協定是會議初始協定 (Session Initiation Protocol，簡稱SIP)，其優點在於簡單、擴展性強，足以承載快速演進的各種多媒體服務。而點對點網路 (Peer-to-Peer，簡稱P2P) 這種不需要中央集權式伺服器的架構，同樣有著良好的擴展性、強韌度與容錯能力，因此很適合、也很常用來做為提供VoIP服務的平台，由目前的趨勢看來，以P2P 為基礎的SIP服務將漸漸普及，使用者也將日益增加。但是隨著P2P SIP服務普及而扮演傳統電話角色時，傳統電話所需處理的問題P2P SIP也將面。其中包括合法監聽就是一個很重要的議題。 目前對於合法監聽方面，已有多項研究正在進行中或已定義出規範，其中對於傳統電話網路的監聽已行之多年。近年來，網際網路多媒體服務發展迅速，由於SIP over P2P網路的傳輸方式與架構與傳統的不同，因此傳統舊有的監聽架構，對於新興的網路多媒體服務，並無法提供相同的監聽效用。 本論文將針對在P2P網路上使用SIP的多媒體服務，提出三個合法的監聽策略。套用本論文的監聽策略，最後將可接近99%的監聽率。 The quality of multimedia services is limited on bandwidth in past few year when people using dial-up or low speed access networks to access the Internet. Due to the development of internet & high bandwidth, multimedia services are getting more and more attractive to people. VoIP is the most popular services among all these multimedia services, and SIP (Session Initiation Protocol) is the most popular protocol among all the VoIP technologies due to its simplicity and scalability to support quickly evolved multimedia services. The P2P network which does not need a central server also has good scalability, robustness and fault tolerance. So it is suitable and often adapted to be the platform to provide the VoIP services. Trend shows that the P2P based SIP will getting popular and play the same role as the PSTN(Public Switched Telephone network), so it will face the same issues that the PSTN faces. Lawful interception is one of the most important topics. To the aspect of lawful interception, there are many researches in progress and specifications are already defined. Among them, the lawful interception of the PSTN has been conducted for many years. With rapid developments of internet multimedia services in recent years, it is more difficult to use traditional methods on monitoring VoIP over P2P networks. So a thesis proposes the lawful interception system to intercept and collect various forms of communications while using VoIP over P2P networks, and proposes three interception strategies for lawful interception. Simulations are done to verify the proposed strategies.
