MGCP終端設備行動化的架構與協定

Abstract

網路電話是近年來受人矚目的熱門話題，它可以提供使用者以市內電話的價格來打長途電話；為了統一網路電話所使用的協定，並且讓gateway有較佳的擴充性，IETF提出了將signaling和data分開處理的架構，把call control的功能從gateway中抽出，獨立出來交由專門的元件Call Agent負責，經過許多發展的過程，演變為Media Gateway Control Protocol (MGCP)。 目前MGCP的設計並沒有提供支援terminal mobility（終端設備行動化）的能力，因此我們針對這個部分加以深入研究，改良MGCP中Call Agent及Media Gateway的功能及對每個終端設備資料的紀錄方式，提出Home Call Agent及Foreign Call Agent的觀念，對於所有的電話號碼提供Numbering plan（編碼計畫），以及加入Directory Server（目錄伺服器）共同運作，並且提出我們發展的Registration（註冊），Roaming（漫遊），Handover（交遞），Deregistration（取消註冊）等通訊協定讓系統能夠處理使用者發生移動的狀況，對於每個號碼位置追蹤的過程變得更為簡單迅速且容易控制，因此藉由使用行動終端設備，使用者可以任意的移動所在的位置，並且能夠隨時（anytime）、隨地（anywhere）接收到系統提供的服務。

In recent years, “Internet telephony” is becoming more popular and is an important trend to the next generation voice communications. It could provide long-distance call services at the cost of local calls. In order to unify the protocols of Internet telephony and improve the scalability of Internet telephony gateways, IETF proposed an Internet telephony structure that separates signaling from data streams by extracting call control functions out from gateways to Call Agents. After several evolutions, IETF proposed the Media Gateway Control Protocol (MGCP). The current specification of MGCP does not support terminal mobility. In this thesis, we focus on the design and implementation of terminal mobility for MGCP. We enhance the functionality of Call Agent and Media Gateway in MGCP by proposing a new location management mechanism to keep tracking of the terminal devices. We provide a systematic numbering plan for all phone numbers, and introduce the concept of Home Call Agents, Foreign Call Agents, and Directory Servers. We also design the communication protocols, Registration, Roaming, Handoff, and Deregistration, required to support terminal mobility. The presented location tracking mechanism is simple and efficient, and is backward compatible with the original static MGCP terminals and media gateways.