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Content for  TS 24.147  Word version:  17.0.0

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1  Scopep. 7

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.
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2  Referencesp. 7

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.
[1]
TR 21.905: "Vocabulary for 3GPP Specifications".
[2]
TS 22.228: "Service requirements for the Internet Protocol (IP) multimedia core network subsystem; Stage 1".
[3]
TS 23.218: "IP Multimedia (IM) session handling; IM call model; Stage 2".
[4]
TS 24.228: Release 5: "Signalling flows for the IP multimedia call control based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
[5]
TS 24.229: "Internet Protocol (IP) multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
[6]
TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
[7]
RFC 3261  (June 2002): "SIP: Session Initiation Protocol".
[8]
RFC 4353  (February 2006): "A Framework for Conferencing with the Session Initiation Protocol (SIP)".
[9]
RFC 4579  ( August 2006): "Session Initiation Protocol Call Control - Conferencing for User Agents".
[10]
RFC 6665  (July 2012): "SIP-Specific Event Notification".
[11]
RFC 4575  (August 2006): "A Session Initiation Protocol (SIP) Event Package for Conference State".
[12]
TS 29.228: "IP Multimedia (IM) Subsystem Cx and Dx Interfaces; Signalling flows and message contents".
[13]  Void.
[14]  Void.
[15]
TS 29.208: "End to end Quality of Service (QoS) signalling flows".
[16]
RFC 2833  (May 2000): "RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals".
[17]
RFC 3515  (April 2003): "The Session Initiation Protocol (SIP) Refer Method".
[18]  Void.
[19]
RFC 3840  (August 2004): "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)".
[20]
RFC 3892  (September 2004): "The Session Initiation Protocol (SIP) Referred-By Mechanism".
[21]  Void.
[22]  Void.
[23]  Void.
[24]  Void.
[25]  Void.
[26]  Void.
[27]  Void.
[28]
RFC 4582  (November 2006): "The Binary Floor Control Protocol (BFCP)".
[29]  Void.
[30]  Void.
[31]  Void.
[32]  Void.
[33]
RFC 3891  (September 2004): "The Session Inititation Protocol (SIP) "Replaces" Header".
[34]
RFC 5366  (October 2008): "Conference Establishment Using Request-Contained Lists in the Session Initiation Protocol (SIP)"
[35]
RFC 4583  (November 2006): "Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams".
[36]
RFC 5360  (October 2008): "A Framework for Consent-Based Communications in the Session Initiation Protocol (SIP)".
[37]
RFC 7989  (October 2016): "End-to-End Session Identification in IP-Based Multimedia Communication Networks".
[38]
TS 24.166: "3GPP IMS Conferencing Management Object (MO)".
[39]
RFC 7647  (September 2015): "Clarifications for the use of REFER with RFC6665".
[40]
RFC 4796  (February 2007): "The Session Description Protocol (SDP) Content Attribute".
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3  Definitions, symbols and abbreviationsp. 9

3.1  Definitionsp. 9

For the purposes of the present document, the terms and definitions given in TS 21.905, and the following apply:
Conferencing AS:
an Application Server that supports functionality specific to a SIP conference focus
Ad-hoc conference:
An unscheduled conference that is created on-the-fly by a conference participant.
 
The following terms and definitions given in TS 23.228 apply (unless otherwise specified):
Public Service Identity
Three-way session
 
For the purposes of the present document, the following terms and definitions given in TS 23.228, subclause 4.3.3.1 and TS 23.228, subclause 4.6 apply:
IP-Connectivity Access Network (IP-CAN)
 
The following terms and definitions given in RFC 4353 apply (unless otherwise specified):
Conference
Conference-Aware Participant
Conference notification service
Conference Policy
Conference-Unaware Participant
Conference URI
Focus
Mixer
Participant
Tightly Coupled Conference
 
The following terms and definitions given in RFC 4579 apply (unless otherwise specified):
Conference Factory URI
 
For the purposes of the present document, the following terms and definitions given in RFC 3840 apply:
Feature parameter
 
For the purposes of the present document, the following terms and definitions given in TS 23.002, subclause 4.1.1.1 and TS 23.002, subclause 4a.7 apply:
Call Session Control Function (CSCF)
Home Subscriber Server (HSS)
Media Gateway Control Function (MGCF)
Multimedia Resource Function Controller (MRFC)
Multimedia Resource Function Processor (MRFP)
 
For the purposes of the present document, the following terms and definitions given in TS 23.218, subclause 3.1 apply:
Filter criteria
Initial filter criteria
Initial request
Subsequent request
 
For the purposes of the present document, the following terms and definitions given in TS 23.228, subclause 4.3.3.1 and TS 23.228, subclause 4.6 apply:
Interrogating-CSCF (I-CSCF)
Proxy-CSCF (P-CSCF)
Public user identity
Serving-CSCF (S-CSCF)
 
For the purposes of the present document, the following terms and definitions given in TR 21.905 apply:
User Equipment (UE)
 
For the purposes of the present document, the following terms and definitions given in RFC 4582 apply:
Floor
Floor chair
Floor control server
Floor participant
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3.2  Abbreviationsp. 10

For the purposes of the present document, the following abbreviations apply:
AMR
Adaptive Multi-Rate
AS
Application Server
BFCP
Binary Floor Control Protocol
CN
Core Network
CSCF
Call Session Control Function
FQDN
Fully Qualified Domain Name
HSS
Home Subscriber Server
I-CSCF
Interrogating CSCF
IM
IP Multimedia
IMS
IP Multimedia CN subsystem
IP
Internet Protocol
IP-CAN
IP-Connectivity Access Network
MGCF
Media Gateway Control Function
MRFC
Multimedia Resource Function Controller
MRFP
Multimedia Resource Function Processor
P-CSCF
Proxy CSCF
PSI
Public Service Identity
S-CSCF
Serving CSCF
SDP
Session Description Protocol
SIP
Session Initiation Protocol
TLS
Transport Layer Security
UE
User Equipment
VBC
Volume Based Charging
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4  Conferencing overviewp. 10

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.
Copy of original 3GPP image for 3GPP TS 24.147, Fig. 4.1: Functional split between the AS, MRFC and MRFP
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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.

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