The present document provides the protocol details for conferencing within the IP Multimedia Core Network subsystem (IMS) based on the Session Initiation Protocol (SIP), SIP Events, the Session Description Protocol (SDP) and the Binary Floor Control Protocol (BFCP). The functionalities for conference policy control (with respective standardised protocols) are felt to be essential for a complete IMS conferencing service but are not specified in this version of IMS conferencing and are for further study. The present document does not cover the signalling between a MRFC and a MRFP. Where possible, the present document specifies the requirements for this protocol by reference to specifications produced by the IETF within the scope of SIP, SIP Events, SDP and BFCP, either directly, or as modified by TS 24.229. Where this is not possible, extensions to SIP are defined within the present document. The document has therefore been structured in order to allow both forms of specification. The present document is applicable to Application Servers (ASs), Multimedia Resource Function Controllers (MRFCs), Multimedia Resource Function Processors (MRFP), Media Gateway Control Functions (MGCFs) and to User Equipment (UE) providing conferencing capabilities.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.

The basic services for the IP Multimedia core network Subsystem (IMS), as defined in TS 24.229, allow a user to initiate, modify and terminate media sessions based on the Session Initiation Protocol, as defined in RFC 3261. Although these basic mechanisms already allow multi party calls, more sophisticated services for communication between multiple parties can be made available by the network. The conferencing service provides the means for a user to create, manage, terminate, join and leave conferences. It also provides the network with the ability to give information about these conferences to the involved parties. The network operator or the user may apply membership and media policies to a conference. The functionality for conference policy control (with a respective standardised protocol) is felt to be essential for a complete IMS conferencing service but is not specified in this version of IMS conferencing and is for further study. Conferencing applies to any kind of media stream by which users may want to communicate, this includes e.g. audio and video media streams as well as instant message based conferences or gaming. Floor control, as part of the conferencing service offers control of shared conference resources at the MRFP using BFCP. The framework for SIP conferences is specified in RFC 4353. The architecture for the 3GPP conference service is specified in TS 23.228 and TS 23.218. The present document specifies the usage of SIP, SDP and BFCP to realize 3GPP conference service based on the protocols specified by the IETF defined conference service as per RFCs listed in clause 2. However, since the IETF conference service has various scenarios and features as described in RFC 4353, 3GPP conference service is a subset of the above IETF defined conference service. Loosely coupled conferencing is outside the scope of this release of the IMS conferencing service. The following figure depicts the functional split for SIP based conferences between the AS, the MRFC and the MRFP.

The conference policy, conference notification server and top-level focus as specified in RFC 4353 are located in the AS. The MRFC has a conference policy and focus as specified in RFC 4353. The mixer and floor control server are located in the MRFP.