ETSI TS 124 147 V18.0.0 (2024-04)

Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Conferencing using the IP Multimedia (IM) Core Network (CN) subsystem; Stage 3 (3GPP TS 24.147 version 18.0.0 Release 18)

RTS/TSGC-0124147vi00

General Information

• Status: Not Published
• Technical Committee: 3GPP CT 1 - MM/CC/SM [lu] (formely CN1)
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 25-Apr-2024

Standards Content (Sample)

TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS);
LTE;
Conferencing using the IP Multimedia (IM) Core Network (CN)
subsystem;
Stage 3
(3GPP TS 24.147 version 18.0.0 Release 18)

3GPP TS 24.147 version 18.0.0 Release 18 1 ETSI TS 124 147 V18.0.0 (2024-04)

Reference
RTS/TSGC-0124147vi00
Keywords
GSM,LTE,UMTS
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ETSI
3GPP TS 24.147 version 18.0.0 Release 18 2 ETSI TS 124 147 V18.0.0 (2024-04)
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Legal Notice
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Modal verbs terminology
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ETSI
3GPP TS 24.147 version 18.0.0 Release 18 3 ETSI TS 124 147 V18.0.0 (2024-04)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 7
2 References . 7
3 Definitions, symbols and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 10
4 Conferencing overview . 10
5 Protocol using SIP and SIP events for conferencing . 12
5.1 Introduction . 12
5.2 Functional entities . 12
5.2.1 User Equipment (UE) . 12
5.2.2 Media Resource Function Controller (MRFC) . 12
5.2.3 Conferencing Application Server (AS) . 12
5.2.4 Media Gateway Control Function (MGCF) . 12
5.3 Role . 12
5.3.1 Conference Participant . 12
5.3.1.1 General . 12
5.3.1.2 Subscription for conference event package . 12
5.3.1.3 Conference creation . 13
5.3.1.3.1 General . 13
5.3.1.3.2 Conference creation with a conference factory URI. 13
5.3.1.3.3 Three-way session creation . 13
5.3.1.4 Joining a conference . 14
5.3.1.4.1 User joining a conference by using a conference URI . 14
5.3.1.4.2 User joining a conference after receipt of a REFER request . 14
5.3.1.4.3 User joining a conference on receipt of a INVITE request. 14
5.3.1.5 Inviting other users to a conference . 14
5.3.1.5.1 General . 14
5.3.1.5.2 User invites other user to a conference by sending a REFER request to the other user . 15
5.3.1.5.3 User invites other user to a conference by sending a REFER request to the conference focus . 15
5.3.1.5.4 User invites other users to a conference by including URI list in initial INVITE request to the
conference focus . 16
5.3.1.6 Leaving a conference . 16
5.3.1.6.1 Conference participant leaving a conference . 16
5.3.1.6.2 Conference focus removes conference participant from a conference . 16
5.3.1.6.3 Removing a conference participant from a conference . 17
5.3.1.7 Consent to list server distribution . 17
5.3.2 Conference Focus . 17
5.3.2.1 General . 17
5.3.2.2 Generic procedures for all conference related methods at the conference focus . 17
5.3.2.2.1 Conference focus originating case . 17
5.3.2.2.2 Conference focus terminating case . 17
5.3.2.3 Conference creation . 18
5.3.2.3.1 Conference creation with a conference factory URI. 18
5.3.2.3.2 Conference creation with a conference URI . 18
5.3.2.4 User joining a conference . 19
5.3.2.4.1 User joining a conference by using a conference URI . 19
5.3.2.5 Invitation of users to a conference . 19
5.3.2.5.1 General . 19
5.3.2.5.2 Request from a user to invite another user to a conference using a REFER request . 19
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5.3.2.5.3 Request from a user to invite another user to a conference using an INVITE request for
conference creation . 20
5.3.2.5.4 Inviting a user to a conference by sending an INVITE request . 20
5.3.2.5.5 Inviting a user to a conference by sending a REFER request . 21
5.3.2.6 Leaving a conference . 21
5.3.2.6.1 Conference participant leaving a conference . 21
5.3.2.6.2 Removing a conference participant from a conference . 21
5.3.2.7 Conference termination . 22
5.3.3 Conference Notification Service . 23
5.3.3.1 General . 23
5.3.3.2 Subscription to conference event package . 23
5.3.3.3 Leaving a conference . 23
5.3.3.4 Conference termination . 23
6 Protocol using SDP for conferencing . 23
6.1 Introduction . 23
6.2 Functional entities . 24
6.2.1 User Equipment (UE) . 24
6.2.2 Media Resource Function Controller (MRFC) . 24
6.2.3 Conferencing Application Server (Conferencing AS) . 24
6.2.4 Media Gateway Control Function (MGCF) . 24
6.3 Role . 24
6.3.1 Conference Participant . 24
6.3.2 Conference Focus . 24
7 Void. . 25
8 Protocol for floor control for conferencing . 25
8.1 Introduction . 25
8.2 Functional entities . 25
8.2.1 User Equipment (UE) . 25
8.2.2 Media Resource Function Processor (MRFP) . 25
8.3 Role . 25
8.3.1 Floor participant . 25
8.3.2 Floor chair . 26
8.3.3 Floor control server . 26
Annex A (informative): Example signalling flows of conferencing operation . 27
A.1 Scope of signalling flows . 27
A.2 Introduction . 27
A.2.1 General . 27
A.2.2 Key required to interpret signalling flows . 27
A.2.3 Overview of signalling flows related to PSI routeing. 27
A.3 Flows demonstrating the creation of a conference . 29
A.3.1 Introduction . 29
A.3.2 User automatically creating a conference with a conference factory URI . 29
A.3.2.1 MRFC/AS is located in user's home network . 29
A.3.2.2 MRFC/AS is not located in user's home network . 46
A.3.3 User automatically creating a conference with a conference URI . 66
A.3.4 User creating a conference by manually dialling . 67
A.3.5 User creating a conference from two existing connections (Three-way session), users in different
networks . 67
A.3.6 User automatically creating a conference with a conference factory URI and inviting some users to the
newly-created conference . 67
A.4 Flows demonstrating a user joining a conference . 84
A.4.1 Introduction . 84
A.4.2 User calling into a conference . 85
A.4.2.1 MRFC/AS is not located in user's home network . 85
A.4.2.1.1 Conference URI resolved by the terminating home network . 85
A.4.2.1.2 Conference URI can be resolved by the originating home network . 110
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A.4.3 User getting invited to a conference . 127
A.4.3.1 MRFC/AS is not located in user's home network . 127
A.4.3.1.1 Conference Participant referring another user to a conference . 127
A.4.3.1.2 User getting referred to a conference by a conference participant . 137
A.4.3.1.3 MRFC/AS invites a user to a conference . 146
A.4.3.1.4 MRFC/AS refers a user to a conference . 166
A.4.4 User requesting IMS to join another user . 177
A.4.4.1 MRFC/AS is located in user's home network . 177
A.4.5 User joins a private conversation to a conference . 185
A.4.5.1 User in a different network . 185
A.5 Flows demonstrating a user subscribing to the conference event package . 185
A.5.1 Introduction . 185
A.5.2 User subscribing to the conference event package . 186
A.5.2.1 MRFC/AS is not located in user's home network . 186
A.6 Flows demonstrating a user leaving a conference . 192
A.6.1 Introduction . 192
A.6.2 User leaving the conference . 192
A.6.2.1 MRFC/AS is located in user's home network . 192
A.6.3 User requesting to remove another user from conference . 198
A.6.4 MRFC/AS drops a user from a conference . 198
A.6.4.1 MRFC/AS is located in user's home network . 198
A.7 Flows demonstrating conference termination . 201
A.7.1 General . 201
A.8 Flows demonstrating usage of hold and resume during conferences . 201
A.9 Flows demonstrating the use of the Replaces header . 202
A.9.1 POTS subscriber invited to a conference . 202
Annex B (normative): SDP a=content attribute "g.3gpp.conf" value . 207
B.1 Introduction . 207
B.2 New value . 207
Annex C (informative): Change history . 208
History . 211

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Foreword
rd
This Technical Specification has been produced by the 3 Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
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1 Scope
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
3GPP 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.
2 References
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] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 22.228: "Service requirements for the Internet Protocol (IP) multimedia core network
subsystem; Stage 1".
[3] 3GPP TS 23.218: "IP Multimedia (IM) session handling; IM call model; Stage 2".
[4] 3GPP 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] 3GPP TS 24.229: "Internet Protocol (IP) multimedia call control protocol based on Session
Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
[6] 3GPP TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
[7] IETF RFC 3261 (June 2002): "SIP: Session Initiation Protocol".
[8] IETF RFC 4353 (February 2006): "A Framework for Conferencing with the Session Initiation
Protocol (SIP)".
[9] IETF RFC 4579 ( August 2006): "Session Initiation Protocol Call Control - Conferencing for User
Agents".
[10] IETF RFC 6665 (July 2012): "SIP-Specific Event Notification".
[11] IETF RFC 4575 (August 2006): "A Session Initiation Protocol (SIP) Event Package for
Conference State".
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[12] 3GPP TS 29.228: "IP Multimedia (IM) Subsystem Cx and Dx Interfaces; Signalling flows and
message contents".
[13] Void.
[14] Void.
[15] 3GPP TS 29.208: "End to end Quality of Service (QoS) signalling flows".
[16] IETF RFC 2833 (May 2000): "RTP Payload for DTMF Digits, Telephony Tones and Telephony
Signals".
[17] IETF RFC 3515 (April 2003): "The Session Initiation Protocol (SIP) Refer Method".
[18] Void.
[19] IETF RFC 3840 (August 2004): "Indicating User Agent Capabilities in the Session Initiation
Protocol (SIP)".
[20] IETF 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] IETF RFC 4582 (November 2006): "The Binary Floor Control Protocol (BFCP)".
[29] Void.
[30] Void.
[31] Void.
[32] Void.
[33] IETF RFC 3891 (September 2004): "The Session Inititation Protocol (SIP) "Replaces" Header".
[34] IETF RFC 5366 (October 2008): "Conference Establishment Using Request-Contained Lists in the
Session Initiation Protocol (SIP)"
[35] IETF RFC 4583 (November 2006): "Session Description Protocol (SDP) Format for Binary Floor
Control Protocol (BFCP) Streams".
[36] IETF RFC 5360 (October 2008): "A Framework for Consent-Based Communications in the
Session Initiation Protocol (SIP)".
[37] IETF RFC 7989 (October 2016): "End-to-End Session Identification in IP-Based Multimedia
Communication Networks".
[38] 3GPP TS 24.166: "3GPP IMS Conferencing Management Object (MO)".
[39] IETF RFC 7647 (September 2015): "Clarifications for the use of REFER with RFC6665".
[40] IETF RFC 4796 (February 2007): "The Session Description Protocol (SDP) Content Attribute".
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3 Definitions, symbols and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in 3GPP TS 21.905 [1], 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 3GPP TS 23.228 [2] apply (unless otherwise specified):
Public Service Identity
Three-way session
For the purposes of the present document, the following terms and definitions given in 3GPP TS 23.228 [6]
subclauses 4.3.3.1 and 4.6 apply:
IP-Connectivity Access Network (IP-CAN)
The following terms and definitions given in RFC 4353 [8] 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 [9] apply (unless otherwise specified):
Conference Factory URI
For the purposes of the present document, the following terms and definitions given in RFC 3840 [19] apply:
Feature parameter
For the purposes of the present document, the following terms and definitions given in 3GPP TS 23.002 [2]
subclauses 4.1.1.1 and 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 3GPP TS 23.218 [5]
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 3GPP TS 23.228 [7]
subclauses 4.3.3.1 and 4.6 apply:
Interrogating-CSCF (I-CSCF)
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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 3GPP TR 21.905 [1] apply:
User Equipment (UE)
For the purposes of the present document, the following terms and definitions given in RFC 4582 [28] apply:
Floor
Floor chair
Floor control server
Floor participant
3.2 Abbreviations
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
4 Conferencing overview
The basic services for the IP Multimedia core network Subsystem (IMS), as defined in 3GPP TS 24.229 [5], allow a
user to initiate, modify and terminate media sessions based on the Session Initiation Protocol, as defined in
RFC 3261 [7]. 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 [8].
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The architecture for the 3GPP conference service is specified in 3GPP TS 23.228 [6] and 3GPP TS 23.218 [3].
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 [8], 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.

AS
Media Conference
Conference Policy
Con ference
Policy Server  Server
Notification Server
Conference
Policy
ISC
Top -l  e vel Conference Focus
Mr
'
S-CSCF
Cr
Mr
MRFC
Media
Conference
Policy
Low- l  e vel Conference Focus
Mp
MRFP
Floor Control
Mixer
Server
RTP /  RT CP  BFCP
Figure 4.1: Functional split between the AS, MRFC and MRFP
The conference policy, conference notification server and top-level focus as specified in RFC 4353 [8] subclause 6 are
located in the AS.
The MRFC has a conference policy and focus as specified in RFC 4353 [8] subclause 6.3.
The mixer and floor control server are located in the MRFP.
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5 Protocol using SIP and SIP events for conferencing
5.1 Introduction
Void
5.2 Functional entities
5.2.1 User Equipment (UE)
For the purpose of SIP based conferences, the UE shall implement the role of a Conference participant as described in
subclause 5.3.1.
5.2.2 Media Resource Function Controller (MRFC)
For the purpose of SIP based conferences, the MRFC shall support the procedures for ad-hoc conferencing as described
in subclause 5.8 of 3GPP TS 24.229 [5] and the procedures for media control of ad-hoc conferencing described in
subclause 10.3 of 3GPP TS 24.229 [5]
For the purpose of SIP based conferences, the MRFC shall regard the MRFP as a mixer, as described in RFC 4353 [8].
5.2.3 Conferencing Application Server (AS)
For the purpose of SIP based conferences, the conferencing AS shall implement the role of a conference focus, as
described in subclause 5.3.2 and as a conference notification service, as described in subclause 5.3.3. The conferencing
AS may implement the role of a conference participant as described in subclause 5.3.1.
rd
The conferencing AS shall use the procedures for 3 party call control as described in subclause 5.7.5 of
3GPP TS 24.229 [5] and the procedures for media control in subclause 10.2 of 3GPP TS 24.229 [5] to implement SIP
based conferences.
5.2.4 Media Gateway Control Function (MGCF)
For the purpose of SIP based conferences, the MGCF shall implement the role of Conference participant as described in
subclauses 5.3.1.3.2, 5.3.1.4.1, 5.3.1.5.4, 5.3.1.6.1 and 5.3.1.6.2. In addition, MGCF shall implement the functions
except the "REFER" function in subclause 5.3.1.3.3.
5.3 Role
5.3.1 Conference Participant
5.3.1.1 General
In addition to the procedures specified in subclause 5.3.1, the conference participant shall support the procedures
specified in 3GPP TS 24.229 [5] appropriate to the functional entity in which the conference participant is implemented.
5.3.1.2 Subscription for conference event package
The conference participant may subscribe to the conference event package, as described in RFC 4575 [11]. If the
SUBSCRIBE request outside the existing INVITE dialog is rejected by a 403 (Forbidden) response, the conference
participant should send a SUBSCRIBE request in the existing INVITE dialog.
If SUBSCRIBE request in the existing INVITE dialog fails, the UE should continue the conference call without
conference event subscription.
ETSI
3GPP TS 24.147 version 18.0.0 Release 18 13 ETSI TS 124 147 V18.0.0 (2024-04)
NOTE: Pre-release 12 networks can support in-dialog SUBSCRIBE requests only. Sending a SUBSCRIBE in the
existing dialog enables the UE to subscribe to the conference event package in this situation.
5.3.1.3 Conference creation
5.3.1.3.1 General
A conference can be created by means of SIP, as described in subclause 5.3.1.3.2 or subclause 5.3.1.3.3.
NOTE: Additionally, creation of a conference can be provided by other means.
The conference participant shall make use of the procedures for session establishment as described in subclauses 5.1.2A
and 5.1.3 of 3GPP TS 24.229 [5] when creating conferences by means of SIP.
5.3.1.3.2 Conference creation with a conference factory URI
Upon a request to create a conference with a conference factory URI, the conference participant shall:
1) generate an initial INVITE request in accordance with subclause 5.1.3.1 of 3GPP TS 24.229 [5]; and
2) set the request URI of the INVITE request to the conference factory URI.
On receiving a 200 (OK) response to the INVITE request with the "isfocus" feature parameter indicated in Contact
header, the conference participant shall store the content of the received Contact header as the conference URI. In
addition to this, the conference participant may subscribe to the conference event package as described in
RFC 4575 [11] by using the stored conference URI.
NOTE 1: A conference participant can decide not to subscribe to the conference event package for conferences with
a large number of attendees, due to, e.g. the signalling traffic caused by the notifications about users
joining or leaving the conference.
NOTE 2: A conference can also be created with a conference URI. The procedures for this case at the conference
participant are identical to those for joining a conference, as described in subclaus
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