A conference is a conversation between multiple participants. There are many different types of conferences, including loosely coupled conferences, fully distributed multiparty conferences and tightly coupled conferences. In this chapter only the latter is described since it is the only one that is of interest to the Internet Protocol Multimedia Subsystem (IMS).

Conferencing is not just limited to audio; the popularity of video and text conferencing, better known as chatting, has been growing rapidly over the past few years. This popularity is due to conferencing's ability to transport files, enabling whiteboard sharing and of course provide simulating face-to-face meetings by exchanging video, all in real time.

8.1 IMS Conferencing Architecture and Principles

8.1.1 SIP Focus/Conferencing AS/MRFC

Figure 8.1 gives an overview of IMS conferencing architecture.

Tightly coupled conferences are hosted at a central point of control to which each conference participant has a connection.

The central point is referred to as a ‘SIP focus’ that is addressed by a public service identity (PSI) that relates to a conference. The focus is the endpoint for all SIP signalling dialogs towards all conference participants. Within IMS the SIP focus is an Application Server (AS) which is co-located with a Multimedia Resource Function Controller (MRFC), which is referred to as ‘Conferencing AS/MRFC’.

8.1.2 Conference Mixer – MRFP

Whilst all the SIP signalling and also the basic conference ...

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