Conference

Description

In 3GPP, a conference is defined as an IP multimedia session with two or more participants. It is a fundamental concept in the IP Multimedia Subsystem (IMS) that enables multi-party communication services. Each conference is managed by a conference focus, which is a centralized entity responsible for hosting the conference, including its creation, maintenance, and manipulation of the media. The conference focus implements the conference policy, which includes rules for talk burst control, priorities, and participant rights. A conference can be uniquely identified by a user, and examples include telepresence sessions and multimedia games where the conference focus may be located in a game server.

The architecture of a conference in IMS involves several key components. The conference focus is typically implemented as a Media Resource Function (MRF) or an Application Server (AS) that supports conferencing. The conference focus interacts with the IMS core network via the ISC interface (IMS Service Control) and uses SIP (Session Initiation Protocol) for session control. The conference policy is managed by the conference focus and can be influenced by the participants through signaling. The media mixing or switching is performed by the MRF, which may include a Media Resource Function Controller (MRFC) and a Media Resource Function Processor (MRFP). The MRFC handles the signaling and control, while the MRFP handles the media processing, such as mixing audio and video streams.

The operation of a conference involves several phases: creation, joining, modification, and termination. A conference is created when a user initiates a session and requests a conference, or when a conference focus is pre-configured. Participants join the conference by sending SIP INVITE requests to the conference focus, which then adds them to the session. The conference focus manages the media streams, ensuring that each participant receives the appropriate media. The conference policy determines how the media is mixed or switched, and it can enforce rules such as who can speak, when, and for how long. For example, in a push-to-talk (PTT) conference, the conference focus implements talk burst control to grant the floor to one participant at a time. Participants can also modify the conference by adding or removing participants, changing the media type, or updating the policy. Termination occurs when the conference is ended by the focus or when all participants leave.

Conferences in 3GPP are standardized in specifications such as 22.228 (Service requirements for the IP multimedia core network subsystem), 22.948 (IMS conferencing), 26.223 (Telephony application server), and 26.923 (IMS multimedia telephony). These specifications define the requirements, architecture, and protocols for conferencing services. The conference focus is a key entity that ensures interoperability and consistent behavior across different implementations. The conference can be uniquely identified by a user, which allows for personalized services and management. The conference focus may be located in the network or in a user device, depending on the deployment scenario.

Conferencing is a critical service in IMS, enabling operators to offer rich multi-party communication experiences. It supports a wide range of applications, from simple audio conferences to advanced telepresence and multimedia games. The flexibility of the conference concept allows for customization of policies and media handling, making it suitable for both consumer and enterprise use cases. As IMS evolves, conferencing continues to be enhanced with new features such as support for high-definition video, immersive telepresence, and integration with WebRTC. The conference focus remains the central entity that orchestrates these complex sessions, ensuring that participants can communicate effectively and efficiently.

Purpose & Motivation

The concept of a conference in 3GPP was introduced to enable multi-party communication services within the IP Multimedia Subsystem (IMS). Traditional telephony services were primarily point-to-point, but as user demands evolved, the need for group communication, such as conference calls, telepresence, and collaborative gaming, became apparent. The conference abstraction provides a standardized way to manage multi-party sessions, ensuring interoperability across different vendors and networks. It solves the problem of coordinating media and signaling among multiple participants, which is inherently more complex than two-party sessions. By defining a conference focus, 3GPP created a centralized entity that can enforce policies, manage media, and provide a consistent user experience.

The motivation for standardizing conferencing in IMS was to support advanced services beyond voice, such as multimedia telephony and rich communication services (RCS). The conference focus allows operators to offer value-added services like group calls, push-to-talk, and video conferencing, which are essential for enterprise and consumer markets. It also enables integration with other IMS services, such as presence and messaging, to create a unified communication experience. The conference concept addresses the limitations of earlier circuit-switched conferencing, which was less flexible and could not easily support multimedia or dynamic policy changes.

Historically, conferencing was introduced in Release 6 of 3GPP, as part of the initial IMS specifications. Over successive releases, the definition and capabilities of conferences have been refined and expanded. The core definition has remained stable, but enhancements have been made to support new media types, improved policy control, and better scalability. The conference focus has become a key building block for many IMS applications, and its importance continues to grow as networks move towards 5G and beyond. The standardization of conferencing ensures that users can enjoy seamless multi-party communication regardless of their device or network, and it provides a foundation for future innovations in collaborative services.