網路多媒體服務之通話控制

Abstract

這幾年來，有很多的力量正驅使著系統供應商提供整合的服務。第一，消費者希望在各式各樣的機器上面可以享受到統一的服務。第二，消費者希望可以不管使用的是哪一種接取服務，不管是WiFi，3G，Ethernet，WiMax，ADSL或CABLE，都能享受到同樣的服務內容。第三，有線系統業者的利潤正在降低，因此他們必須開始在無線的領域尋找機會，而無線系統業者的成長速度減慢，也使他們開始探索如何擴大市場。最後，無線與有線業者之間的競爭將會驅使網路服務邁向整合，而網際網路上的某些語音服務的成功案例，如Yahoo! Messenger和Skype等，則使得網際網路應用在網路服務邁向整合的過程中佔了舉足輕重的角色。 由於使用者對行動通訊需求越來越高, 他們希望在任何地方都能無線的連接Internet。3GPP所定義的IP Multimedia Subsystem (IMS) 因此而變得更加重要。本論文中，我們分別就網路多媒體服務的各層面討論設計的議題。在網路電話的整合網路中，我們提出了一個整合的架構稱為Integrated Call Agent (iCA)。iCA整合了網路通訊中的Media Gateway Control Protocol (MGCP)、Session Initiation Protocol (SIP) 與H.323三個主要的協定，讓使用者可以在整合的服務中沒有障礙的互通。我們參考Intelligent Network (IN) 並提出了很彈性的架構，讓將來整合進更多協定成為可能並且所花的心力降到最低。 針對使用者的身分認證問題，3GPP制定了two-pass authentication程序，分別為General Packet Radio Service (GPRS) 網路以及IMS網路認證使用者。我們發現在two-pass authentication中有許多重覆的步驟，因此在論文中我們提出了one-pass authentication的方法，以GPRS網路執行相同的認證程序，但IMS網路以簡化的方法在使用者註冊過程完成認證。我們證明one-pass authentication可以正確的認證使用者，同時省下50%的訊息交換。 在網路多媒體服務中的服務平台中，我們探討了SIP基礎的網路電話客服中心的設計與實作，並且提出了等待時間的演算法。我們設計了兩個評量預測準確度的方法並且發展了一個模擬模型來測量演算法的準確度。我們發現所提出的演算法可以有效的控制使用者等待超時的機率。 以上的研究成果提供讀者在研究網路多媒體服務的通話控制以及身分認證的議題上，可供參考之基礎。

In recent years, there are many forces urging operators to provide the converged services. First, customers hope to enjoy unified services on different type of devices. Second, users want to have uniform services and contents regardless of the kind of underlying access network being used, such as WiFi, 3G, ethernet, WiMax, ADSL, or cable. Third, fixed network providers’ profit is reducing, so they must begin to look for the opportunities in wireless domain. And wireless operators’ speed of growth slows down, makes them begin to explore how to expand their markets. Finally, the competition between the fixed and wireless carriers will drive the network service toward convergence, and some successful cases of Internet telecommunications services such as Yahoo! Messenger and Skype, etc., make Internet Protocol (IP) applications take very important role during the process toward convergence. As consumers become increasingly mobile, they will demand wireless Internet access from everywhere. In keeping with these requirements of end users, IP Multimedia Subsystem (IMS) standards based on the 3GPP UMTS become more and more important. In the IMS system, we propose an integrated call agent of the converged VoIP network. We presente a simple, flexible framework for the interworking functions of VoIP protocols such as Media Gateway Control Protocol (MGCP), Session Initiation Protocol (SIP) and H.323 base on Intelligent Network (IN). In UMTS two-pass authentication, many steps in the General Packet Radio Service (GPRS) authentication and IMS authentication are duplicated. Therefore, we propose an one-pass authentication procedure, in which only the GPRS authentication procedure is performed. In the IMS network, the authentication is implicitly executed in the IMS registration. We formally prove that the IMS user is correctly authenticated, and the one-pass authentication saves up to 50% of the IMS registration/authentication traffic. In the service platform of IP multimedia services, we describe the design and implementation of a SIP-based VoIP call center with waiting time prediction. The SIP-based plug-in modular call center architecture and detailed message flows are elaborated. We propose two output measures and develop a discrete event simulation model to investigate the performance of the waiting time prediction algorithm for the call center. These research results presented in this dissertation can be viewed as a useful foundation for further study in call control for IP multimedia services and authentication.