ETSI TS 124 237 V15.6.0 (2019-10)

ETSI TS 124 237 V15.6.0 (2019-10)






TECHNICAL SPECIFICATION
Universal Mobile Telecommunications System (UMTS);
LTE;
IP Multimedia (IM) Core Network (CN)
subsystem IP Multimedia Subsystem (IMS) service continuity;
Stage 3
(3GPP TS 24.237 version 15.6.0 Release 15)



---------------------- Page: 1 ----------------------
3GPP TS 24.237 version 15.6.0 Release 15 1 ETSI TS 124 237 V15.6.0 (2019-10)



Reference
RTS/TSGC-0124237vf60
Keywords
LTE,UMTS
ETSI
650 Route des Lucioles
F-06921 Sophia Antipolis Cedex - FRANCE

Tel.: +33 4 92 94 42 00  Fax: +33 4 93 65 47 16

Siret N° 348 623 562 00017 - NAF 742 C
Association à but non lucratif enregistrée à la
Sous-Préfecture de Grasse (06) N° 7803/88

Important notice
The present document can be downloaded from:
http://www.etsi.org/standards-search
The present document may be made available in electronic versions and/or in print. The content of any electronic and/or
print versions of the present document shall not be modified without the prior written authorization of ETSI. In case of any
existing or perceived difference in contents between such versions and/or in print, the prevailing version of an ETSI
deliverable is the one made publicly available in PDF format at www.etsi.org/deliver.
Users of the present document should be aware that the document may be subject to revision or change of status.
Information on the current status of this and other ETSI documents is available at
https://portal.etsi.org/TB/ETSIDeliverableStatus.aspx
If you find errors in the present document, please send your comment to one of the following services:
https://portal.etsi.org/People/CommiteeSupportStaff.aspx
Copyright Notification
No part may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying
and microfilm except as authorized by written permission of ETSI.
The content of the PDF version shall not be modified without the written authorization of ETSI.
The copyright and the foregoing restriction extend to reproduction in all media.

© ETSI 2019.
All rights reserved.

DECT™, PLUGTESTS™, UMTS™ and the ETSI logo are trademarks of ETSI registered for the benefit of its Members.

3GPP™ and LTE™ are trademarks of ETSI registered for the benefit of its Members and
of the 3GPP Organizational Partners.
oneM2M™ logo is a trademark of ETSI registered for the benefit of its Members and
of the oneM2M Partners.
®
GSM and the GSM logo are trademarks registered and owned by the GSM Association.
ETSI

---------------------- Page: 2 ----------------------
3GPP TS 24.237 version 15.6.0 Release 15 2 ETSI TS 124 237 V15.6.0 (2019-10)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Legal Notice
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).
The present document may refer to technical specifications or reports using their 3GPP identities. These shall be
interpreted as being references to the corresponding ETSI deliverables.
The cross reference between 3GPP and ETSI identities can be found under http://webapp.etsi.org/key/queryform.asp.
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
ETSI

---------------------- Page: 3 ----------------------
3GPP TS 24.237 version 15.6.0 Release 15 3 ETSI TS 124 237 V15.6.0 (2019-10)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 15
1 Scope . 16
2 References . 16
3 Definitions and abbreviations . 20
3.1 Definitions . 20
3.2 Abbreviations . 23
4 Overview of IP Multimedia (IM) Core Network (CN) subsystem Service Continuity . 24
4.1 General . 24
4.2 Underlying network capabilities . 25
4.2.1 General . 25
4.2.2 PS-CS session continuity, Single Radio . 25
4.2.3 PS to CS and CS to PS session continuity, dual radio access transfer . 26
4.3 URI and address assignments . 26
4.4 Support of session continuity in enterprise scenarios . 27
4.5 Guidelines for use of media feature tags or feature capability indicators . 27
5 Functional entities . 27
5.1 Introduction . 27
5.2 User Equipment (UE) . 27
5.3 Application Server (AS) . 28
5.4 MSC server . 28
5.5 EATF . 29
5.6 Access Transfer Control Function (ATCF) . 30
5.7 Access Transfer Gateway (ATGW) . 30
6 Roles for registration in the IM CN subsystem for service continuity . 31
6.1 Introduction . 31
6.2 SC UE . 31
6.2.1 Distinction of requests . 31
6.2.2 General . 31
6.2.3 SC UE receiving the ATGW information for CS to PS SRVCC . 31
6.3 SCC AS . 32
6.3.1 General . 32
6.3.2 Triggers for the SCC AS providing information to ATCF . 32
6.3.3 SCC AS providing the PS to CS SRVCC related information to the ATCF . 33
6.3.4 Triggers for the SCC AS providing information to MSC server . 34
6.3.5 SCC AS providing the CS to PS SRVCC information to the MSC server . 35
6.4 MSC server . 35
6.4.1 Distinction of requests . 35
6.4.2 General . 35
6.4.3 MSC server receiving the MSC information for CS to PS SRVCC . 35
6.5 Access Transfer Control Function (ATCF) . 36
6.5.1 Distinction of requests . 36
6.5.2 Registration related procedures in the ATCF . 36
6.5.3 ATCF receiving the SRVCC-related information . 38
6.5.4 ATCF sending the ATGW information for CS to PS SRVCC . 39
6.5.5 ATCF receiving the UE information for CS to PS SRVCC . 39
6A Roles for General Capabilities . 39
6A.1 Introduction . 39
6A.2 UE roles . 40
6A.2.1 Operator policy enforcement . 40
ETSI

---------------------- Page: 4 ----------------------
3GPP TS 24.237 version 15.6.0 Release 15 4 ETSI TS 124 237 V15.6.0 (2019-10)
6A.2.2 Signalling elements . 40
6A.2.2.1 Common SIP message set up procedures . 40
6A.2.2.2 SIP INVITE request . 40
6A.3 ATCF . 41
6A.3.1 SRVCC information bound to the registration path . 41
6A.4 SCC AS . 42
6A.4.1 Common SIP message set up procedures . 42
6A.4.2 SIP INVITE request . 42
6A.4.3 SIP INVITE responses towards the SC UE . 42
6A.4.3A SIP INVITE responses towards the MSC server . 44
6A.4.4 Handling of OMR specific attributes . 45
6A.4.5 Target refresh request for a dialog and associated responses . 45
6A.4.6 Rejecting malicious SIP REFER requests from remote UE . 46
6A.4.7 Protecting from malicious SIP INFO requests with remote leg information from remote UE . 46
6A.4.8 Precondition and access transfer . 46
6A.5 SDP media description conflict between target and remote access leg . 47
6A.6 Indicating traffic leg . 47
6A.6.1 The SCC AS server procedure for indicating traffic leg . 47
6A.6.2 The MSC server procedure for indicating traffic leg . 47
6A.6.3 The ATCF server procedure for indicating traffic leg . 47
6A.7 MSC server . 48
6A.7.1 Precondition and access transfer . 48
7 Roles for call origination for service continuity . 48
7.1 Introduction . 48
7.2 SC UE . 48
7.2.1 General . 48
7.2.2 Additional procedures with MSC server assisted mid-call feature . 49
7.3 SCC AS . 49
7.3.1 Distinction of requests sent to the SCC AS . 49
7.3.2 Call origination procedures at the SCC AS . 49
7.3.3 Subscription related procedures in the SCC AS . 50
7.4 EATF . 50
7.4.1 Distinction of requests sent to the EATF . 50
7.4.2 Call origination procedures at the EATF . 51
7.5 Access Transfer Control Function (ATCF) . 52
7.5.1 Distinction of requests . 52
7.5.2 Call origination procedures in the ATCF . 52
7.5.2.1 General . 52
7.5.2.2 Sessions originated in PS domain . 52
7.5.2.3 Sessions originated in CS domain . 53
7.5.3 Procedures in the ATCF for originating requests not related to a call . 55
7.6 MSC server . 55
7.6.1 Call origination procedures . 55
8 Roles for call termination for service continuity . 56
8.1 Introduction . 56
8.2 SC UE . 56
8.3 SCC AS . 57
8.3.1 Distinction of requests sent to the SCC AS . 57
8.3.2 Call termination procedures in the SCC AS . 57
8.4 Access Transfer Control Function (ATCF) . 59
8.4.1 Distinction of requests . 59
8.4.2 Call termination procedures in the ATCF . 59
8.4.2.1 General . 59
8.4.2.2 Sessions terminated in PS domain . 59
8.4.2.3 Sessions terminated in CS domain . 60
8.5 MSC server . 62
8.5.1 Distinction of requests . 62
8.5.2 Call termination procedures . 62
8.5.2.1 SIP INVITE request from home network . 62
8.5.2.2 SIP INVITE request from ATCF . 62
ETSI

---------------------- Page: 5 ----------------------
3GPP TS 24.237 version 15.6.0 Release 15 5 ETSI TS 124 237 V15.6.0 (2019-10)
9 Roles for PS-CS access transfer . 63
9.1 Introduction . 63
9.1A Additional procedures with MSC Server assisted mid-call feature . 63
9.2 SC UE . 64
9.2.0 General . 64
9.2.1 SC UE not using ICS procedures for PS to CS access transfer . 64
9.2.1AAA SC UE not using ICS procedures for PS to CS access transfer of emergency session . 66
9.2.1AA SC UE using ICS procedures for PS to CS access transfer . 66
9.2.1A SC UE procedures for PS to CS access transfer with MSC server assisted mid-call feature . 67
9.2.1B SC UE procedures for PS to CS access transfer with MSC server assisted mid-call feature for speech
and video session . 70
9.2.2 SC UE procedures for CS to PS access transfer . 71
9.2.2.1 Distinction of request . 71
9.2.2.2 SC UE procedure for transferring the first CS call . 71
9.2.3 SC UE procedures for CS to PS access transfer with MSC server assisted mid-call feature . 72
9.2.4 SC UE procedures for selecting a session in an early dialog phase to be transferred using PS to CS
dual radio access transfer procedure . 73
9.2.5 SC UE procedures for CS to PS dual radio access transfer of calls in an early phase . 74
9.2.5.1 Conditions for CS to PS dual radio access transfer of calls in originating pre-alerting or in the
alerting phase . 74
9.2.5.2 SC UE procedure for CS to PS dual radio access transfer of calls in originating pre-alerting or in
the alerting phase . 75
9.2.5.3 SC UE procedures for transferring an additional CS session in an early phase . 76
9.3 SCC AS . 77
9.3.0 General . 77
9.3.1 Distinction of requests sent to the SCC AS . 77
9.3.2 SCC AS procedures for PS to CS access transfer . 77
9.3.2A SCC AS procedures for PS to CS access transfer with MSC server assisted mid-call feature . 81
9.3.3 SCC AS procedures for CS to PS access transfer . 85
9.3.4 SCC AS procedures for CS to PS access transfer with MSC server assisted mid-call feature . 86
9.3.5 SCC AS procedures for PS to CS dual radio access transfer of calls in an early dialog phase . 88
9.3.5.1 Conditions for selecting a sessions in an early dialog phase . 88
9.3.5.2 SCC AS procedures for PS to CS dual radio access transfer of a originating session in the
alerting phase . 89
9.3.5.3 SCC AS procedures for PS to CS dual radio, access transfer of a originating session in the pre-
alerting phase . 91
9.3.5.4 SCC AS procedures for PS to CS dual radio access transfer of an additional session in an early
dialog phase. 93
9.3.5.5 SCC AS procedures for PS to CS dual radio access transfer of a terminating session in the
alerting phase . 94
9.3.6 Removal of non-transferred audio media components and release of source access legs. 95
9.3.7 SCC AS procedures for CS to PS dual radio access transfer for calls in an early phase . 96
9.3.7.1 Conditions for transferring dialog(s) in the originating pre-alerting or the alerting dialog phase . 96
9.3.7.2 SCC AS procedures for CS to PS dual radio access transfer for originating calls in pre-alerting
phase or in alerting phase on the originating side . 96
9.3.7.3 SCC AS procedures for CS to PS dual radio access transfer for a call in the alerting phase on the
terminating side . 98
9.3.7.4 SCC AS procedures for PS to CS dual radio access transfer of an additional session in an early
dialog phase. 99
9.4 MSC server enhanced for ICS . 102
9.4.1 Void . 102
9.4.1A Void . 102
9.5 PS to CS session continuity with MSC server assisted mid-call feature . 102
9.6 PS to CS session cont
...