Study Of A SIP-based Cascaded Tightly Coupled Conference Control System

SIP is a multimedia session control protocol for IP network. Replacing H.323, SIP will be the basic protocol in developing next-generation Internet multimedia applications because it can take advantage of NGN and 3G. Since SIP never supports network multimedia conferenc directly and there is no an applied SIP-based network conference control system, it is valuable and necessary to study it.The functionality of a network conference control system includes application control, menbership control, floor management, network management and meta conference management. A real applied system needn't realize all of them but some. In this article, we study the last four functions, which are more relative with SIP, and analyze the special points base on SIP, then create a cascaded tightly coupled conference control model.To develop a cascaded model, the model unifies the service provider and service by abtracting the conference server as a conference. The model creates conference domain name system to discribe this hiberarchy. The model realizes a zero coupling machanism to extend easily and flexibly by taking a function module as a conference user. The module also supports very large conference by distribution.The model describes a real conference in three kind of policies: conference policy, user policy and media policy. To help SIP in conference management, the model refers to an extendtion of SIP URI parameter: isfocus and creates conference description protocol(CDP). CDP can describe all policis about a conference in text format. CDP helps server and user agent to exchange and modify information about the conference.This Article realizes the model in SIP, details the message formats and sequences. The realization is completely compatible with the latest version of SIP: RFC 3261.Cascaded tightly coupled conference control model is a SIP-based conference control model with rich functions. It is worth of developing applied system and helpful to study SIP-based conference control system and multimedia applications.