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TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS);
LTE;
IP Multimedia Subsystem (IMS) Service Continuity;
Stage 2
(3GPP TS 23.237 version 15.1.0 Release 15)
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3GPP TS 23.237 version 15.1.0 Release 15 1 ETSI TS 123 237 V15.1.0 (2018-07)
Reference
RTS/TSGS-0223237vf10
Keywords
GSM,LTE,UMTS
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ETSI
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3GPP TS 23.237 version 15.1.0 Release 15 2 ETSI TS 123 237 V15.1.0 (2018-07)
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.
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ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
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Foreword
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, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
.
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
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3GPP TS 23.237 version 15.1.0 Release 15 3 ETSI TS 123 237 V15.1.0 (2018-07)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 9
Introduction . 9
1 Scope . 10
2 References . 10
3 Definitions, symbols and abbreviations . 12
3.1 Definitions . 12
3.2 Abbreviations . 14
4 High level principles and architectural requirements . 14
4.1 Basic Assumptions . 14
4.1.0 General . 14
4.1.1 PS-CS Access Transfer . 14
4.1.2 PS-PS Access Transfer . 15
4.1.3 Inter-UE Transfer . 15
4.2 Architectural Requirements . 16
4.2.1 General Requirements . 16
4.2.2 Access Transfer Requirements . 16
4.2.3 IUT Requirements . 17
4.3 Service Continuity . 18
4.3.1 Session Transfer concepts . 18
4.3.1.1 General . 18
4.3.1.2 Access Transfer concepts . 19
4.3.1.2.1 General Access Transfer concepts . 19
4.3.1.2.2 Access Transfer (PS – CS) concepts . 19
4.3.1.2.2A MSC Server assisted mid-call feature . 20
4.3.1.2.3 Co-existence of ICS UE and MSC Server assisted mid-call feature . 20
4.3.1.3 Inter-UE Transfer concepts . 20
4.3.1.3.1 General . 20
4.3.1.3.2 Controller UE and Controllee UE operations . 21
4.3.1.3.2.1 Overview . 21
4.3.2 Void . 21
4.3.3 Information used for IMS Service Continuity . 21
5 Architecture model and reference points . 22
5.1 Overview . 22
5.2 Reference Architecture for non emergency session . 22
5.2.1 General . 22
5.2.2 Architecture when using ATCF enhancements. 22
5.3 Functional Entities . 23
5.3.1 SCC AS . 23
5.3.2 IMS Service Continuity UE . 25
5.3.2.1 Access Transfer Functions . 25
5.3.2.2 IUT Functions and Roles . 25
5.3.2.2.1 Functions . 25
5.3.2.2.2 Controller UE Role . 25
5.3.2.2.3 Controllee UE Role . 26
5.3.3 Emergency Access Transfer Function (EATF) . 26
5.3.4 Access Transfer Control Function (ATCF) . 26
5.3.4.1 General . 26
5.3.4.2 ATCF inclusion . 27
5.3.5 Access Transfer Gateway (ATGW) . 28
5.3.6 HSS . 28
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3GPP TS 23.237 version 15.1.0 Release 15 4 ETSI TS 123 237 V15.1.0 (2018-07)
5.3.7 MSC Server . 28
5.4 Signalling and bearer paths for IMS Service Continuity . 28
5.4.1 General . 28
5.4.2 Sessions with PS media flow(s) . 28
5.4.2a Sessions with PS media flow(s) using ATCF . 29
5.4.3 Sessions with CS media . 29
5.4.3a Sessions with CS media flow(s) using ATCF . 29
5.5 IUT Collaborative Sessions . 30
5.6 Reference Architecture for SRVCC emergency session . 31
6 Procedures and flows for Access Transfer . 31
6.0 Introduction . 31
6.1 Registration . 31
6.1.1 General . 31
6.1.2 Registration using ATCF enhancements. 31
6.1.3 Registration: CS to PS - Single Radio . 33
6.1.3.1 IMS Registration by UE . 33
6.1.3.2 UE IMS Registration change update . 33
6.2 Origination and Termination . 34
6.2.1 Origination . 34
6.2.1.1 Origination Procedures . 34
6.2.1.2 Originating sessions that use CS media . 34
6.2.1.3 Originating sessions that use only PS media flow(s) . 35
6.2.1.3a Originating sessions that use only PS media flow(s) - fallback to CS domain in pre-alerting phase . 36
6.2.1.4 Originating sessions for (v)SRVCC that use ATCF enhancements . 37
6.2.1.5 Originating sessions for CS to PS - Single Radio . 37
6.2.2 Termination. 38
6.2.2.1 Termination Procedures . 38
6.2.2.2 Terminating sessions that use CS media . 38
6.2.2.3 Terminating sessions that use only PS media flow(s) . 39
6.2.2.3a Terminating sessions that use only PS media flow(s) - fallback to CS domain in pre-alerting
phase . 40
6.2.2.4 Terminating sessions over Gm where speech media is not accepted by the UE . 41
6.2.2.5 Terminating sessions for (v)SRVCC that use ATCF enhancements . 42
6.2.2.6 Terminating sessions for CS to PS - Single Radio . 42
6.3 Access Transfer . 43
6.3.1 Access Transfer Procedure . 43
6.3.1.1 Introduction . 43
6.3.1.2 Access Transfer Procedures . 43
6.3.1.2a Access Transfer Procedures using ATCF enhancements . 44
6.3.1.3 Enablement of Access Transfer procedures . 44
6.3.1.3a Enablement of Access Transfer procedures using ATCF enhancements . 45
6.3.1.4 Execution of Access Transfer procedures . 45
6.3.1.4a Execution of Access Transfer procedures using ATCF enhancements . 45
6.3.1.5 Remote Leg Update. 45
6.3.1.6 Source Access Leg Release . 46
6.3.1.7 Access Transfer Information for ATCF . 46
6.3.2 Access Transfer Information flows . 47
6.3.2.0 General . 47
6.3.2.1 PS – CS Access Transfer . 47
6.3.2.1.1 PS – CS Access Transfer: PS to CS - Dual Radio . 47
6.3.2.1.1a PS – CS Access Transfer: PS to CS – Dual Radio with Session State Information . 48
6.3.2.1.2 PS – CS Access Transfer: CS to PS - Dual Radio . 49
6.3.2.1.2a PS – CS Access Transfer: CS to PS – Dual Radio with Session State Information . 50
6.3.2.1.2b CS - PS Access Transfer: CS to PS - Dual Radio, incoming voice call in alerting phase . 51
6.3.2.1.2c CS - PS Access Transfer: CS to PS - Dual Radio, outgoing voice call in pre-alerting state or
in alerting phase . 51
6.3.2.1.2d PS - CS Access Transfer: PS to CS - Dual Radio, outgoing voice or video call in pre-alerting
state or in alerting phase . 51
6.3.2.1.2e PS - CS Access Transfer: PS to CS - Dual Radio, incoming voice call in alerting phase . 53
6.3.2.1.3 Subsequent Access Transfers . 54
6.3.2.1.4 PS – CS Access Transfer: PS to CS – Single Radio . 54
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3GPP TS 23.237 version 15.1.0 Release 15 5 ETSI TS 123 237 V15.1.0 (2018-07)
6.3.2.1.4a PS – CS Access Transfer: PS to CS – Single Radio with Session State Information . 56
6.3.2.1.4b PS to CS Access Transfer: PS to CS – Single Radio; using I1 reference point . 58
6.3.2.1.4c PS - CS Access Transfer: PS to CS - Single Radio, incoming voice or video call in pre-
alerting or alerting phase . 59
6.3.2.1.4d PS - CS Access Transfer: PS to CS - Single Radio, outgoing voice or video call in pre-
alerting state or in alerting phase . 61
6.3.2.1.4e PS - CS Access Transfer: PS to CS - Single Radio, voice and video . 63
6.3.2.1.5 PS – CS Access Transfer for voice and video, Dual Radio . 65
6.3.2.1.6 PS – CS Access Transfer: PS to CS – Dual Radio, mid-call service with an active speech and
video session . 66
6.3.2.1.7 PS – CS Access Transfer: PS to CS – Dual Radio, mid-call service with one inactive speech
and video session . 66
6.3.2.1.7a PS - CS Access Transfer: PS to CS - Single Radio, mid-call service with an incoming waiting
call in alerting phase . 67
6.3.2.1.7b PS - CS Access Transfer: PS to CS - Single Radio, mid-call service with an outgoing call in
pre-alerting state or in alerting phase. 69
6.3.2.1.7c PS - CS Access Transfer: PS to CS - Single Radio, mid-call service with an incoming call in
alerting phase and a held session . 71
6.3.2.1.8 PS - CS Access Transfer: Conferencing - for UEs not using ICS capabilities . 73
6.3.2.1.9 PS – CS Access Transfer: PS to CS – Single Radio using ATCF enhancements . 74
6.3.2.1.10 PS - CS Access Transfer: CS to PS - Single Radio . 77
6.3.2.2 PS - PS Access Transfer . 80
6.3.2.2.1 PS-PS Access Transfer with full media transfer . 80
6.3.2.2.2 PS-PS Access Transfer with partial media transfer . 81
6.3.2.2.3 PS-PS Access Transfer with full media transfer for an incoming call in early dialog phase . 81
6.3.2.2.4 PS-PS Access Transfer with full media transfer for an outgoing call in early dialog phase . 83
6.3.2.3 PS - PS in conjunction with PS - CS Access Transfer . 84
6.3.2.3.1 PS - PS in conjunction with PS - CS Access Transfer: PS to CS for UEs not using ICS
capabilities . 84
6.3.2.3.2 PS - PS in conjunction with PS - CS Access Transfer: CS to PS for UEs not using ICS
capabilities . 86
6.3.2.3.3 PS – PS in conjunction with PS - CS Access Transfer: PS to CS for UEs with ICS capabilities
- Using Gm reference point . 86
6.3.2.3.4 PS - PS in conjunction with PS - CS Access Transfer: CS to PS for UEs with ICS capabilities
- Using Gm reference point . 88
6.3.2.3.5 PS – PS in conjunction with PS – CS Access Transfer: Active/Held sessions - Using Gm
reference point . 88
6.3.2.3.6 PS – PS in conjunction with PS – CS Access Transfer: Explicit Communication Transfer -
Using Gm reference point. 89
6.3.2.3.7 PS – PS in conjunction with PS – CS Access Transfer: Conferencing - Using Gm reference
point . 89
6.3.2.3.8 PS – PS in conjunction with PS – CS Access Transfer: PS to CS – using I1 reference point . 89
6.3.2.3.9 PS - PS in conjunction with PS - CS Access Transfer: CS to PS - using I1 reference point . 91
6.3.2.3.10 PS - PS in conjunction with PS - CS Access Transfer: PS to CS for Active/Held sessions -
using I1 reference point . 91
6.3.2.3.11 PS - PS in conjunction with PS - CS Access Transfer: CS to PS for Active/Held sessions -
using I1 reference point . 92
6.3.3 Media Adding/Deleting . 92
6.3.3.1 Local End Initiation case: Adding new PS media to existing CS session . 92
6.3.3.2 Local End Initiation case: Incorporating existing CS media in new IMS Session and Gm Service
Control . 93
6.3.3.3 Local End Initiation case: Adding PS media to IMS session with CS media . 94
6.3.3.4 Remote End Initiation case: Adding new PS media to existing CS session . 95
6.3.3.5 Remote End Initiation case: Incorporating existing CS media in new IMS Session and Gm
Service Control . 96
6.3.3.6 Remote End Initiation case: Adding PS media to IMS session with CS media . 97
6.3.3.7 Local End Initiation case – Removing media from split CS and PS sessions . 98
6.3.3.8 Remote End Initiation case – Removing media from split CS and PS sessions . 99
6.3.3.9 Local End Initiation case: Adding new PS media to existing PS session. 100
6.3.3.10 Remote E
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