ETSI TS 123 216 V15.3.0 (2019-10)

Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Single Radio Voice Call Continuity (SRVCC); Stage 2 (3GPP TS 23.216 version 15.3.0 Release 15)

RTS/TSGS-0223216vf30

General Information

• Status: Published
• Publication Date: 30-Sep-2019
• Technical Committee: 3GPP SA 2 - Architecture
• Current Stage: 12 - Completion
• Completion Date: 01-Oct-2019

Standards Content (Sample)

TECHNICAL SPECIFICATION
Digital cellular telecommunications system (Phase 2+) (GSM);
Universal Mobile Telecommunications System (UMTS);
LTE;
Single Radio Voice Call Continuity (SRVCC);
Stage 2
(3GPP TS 23.216 version 15.3.0 Release 15)

3GPP TS 23.216 version 15.3.0 Release 15 1 ETSI TS 123 216 V15.3.0 (2019-10)

Reference
RTS/TSGS-0223216vf30
Keywords
GSM,LTE,UMTS
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ETSI
3GPP TS 23.216 version 15.3.0 Release 15 2 ETSI TS 123 216 V15.3.0 (2019-10)
Intellectual Property Rights
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Legal Notice
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Modal verbs terminology
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ETSI
3GPP TS 23.216 version 15.3.0 Release 15 3 ETSI TS 123 216 V15.3.0 (2019-10)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 7
2 References . 7
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 10
4 High level Principles and Concepts . 10
4.1 High level Principle s . 10
4.1.1 Architectural Principles for 3GPP2 1xCS SRVCC . 10
4.1.2 Architectural Principles for SRVCC and vSRVCC to 3GPP UTRAN/GERAN . 11
4.1.3 Architectural Principles for SRVCC to 3GPP E-UTRAN/UTRAN (HSPA) . 11
4.2 Concepts . 12
4.2.1 E-UTRAN to 3GPP2 1xCS SRVCC . 12
4.2.2 E-UTRAN to 3GPP UTRAN/GERAN SRVCC . 12
4.2.2a E-UTRAN to 3GPP UTRAN vSRVCC . 13
4.2.3 UTRAN (HSPA) to 3GPP UTRAN/GERAN SRVCC . 14
4.2.4 SRVCC for IMS emergency sessions . 15
4.2.4.1 E-UTRAN/UTRAN (HSPA) to 3GPP UTRAN/GERAN . 15
4.2.4.2 E-UTRAN to 3GPP2 1xCS . 16
4.2.4.3 SRVCC in Limited Service Mode . 17
4.2.4.3.1 E-UTRAN/UTRAN (HSPA) to 3GPP UTRAN/GERAN . 17
4.2.4.3.2 E-UTRAN to 3GPP2 1xCS . 17
4.2.4.4 eCall over IMS . 18
4.2.5 Void . 18
4.2.6 CS to PS SRVCC . 18
5 Architecture model and reference points . 19
5.1 General . 19
5.2 Reference architecture . 19
5.2.1 E-UTRAN to 3GPP2 1xCS SRVCC architecture . 19
5.2.2 E-UTRAN to 3GPP UTRAN/GERAN SRVCC architecture . 19
5.2.2a 3GPP E-UTRAN to 3GPP UTRAN vSRVCC architecture . 20
5.2.3 UTRAN (HSPA) to 3GPP UTRAN/GERAN SRVCC architecture . 21
5.2.4 3GPP UTRAN/GERAN to 3GPP E-UTRAN or UTRAN (HSPA) SRVCC architecture . 21
5.2.5 3GPP GERAN to 3GPP UTRAN (HSPA) SRVCC architecture . 22
5.3 Functional Entities . 23
5.3.1 3GPP2 1x CS SRVCC interworking solution function (1xCS IWS) . 23
5.3.2 MSC Server enhanced for E-UTRAN/UTRAN (HSPA) to 3GPP UTRAN/GERAN SRVCC . 23
5.3.2a MSC Server enhanced for vSRVCC . 24
5.3.2b MSC Server enhanced for CS to PS SRVCC. 24
5.3.3 MME . 24
5.3.3.1 Interworking with 3GPP2 1xCS IWS . 24
5.3.3.1.1 Interworking with 3GPP2 1xCS IWS . 24
5.3.3.1.2 Selection of 3GPP2 1xCS IWS . 25
5.3.3.2 Interworking with 3GPP MSC Server enhanced for SRVCC from E-UTRAN / UTRAN (HSPA)
to 3GPP UTRAN/GERAN . 25
5.3.3.2.1 Interworking with 3GPP MSC Server enhanced for (v)SRVCC . 25
5.3.3.2.2 PS bearer splitting function . 26
5.3.3.2.3 Selection of MSC enhanced for SRVCC . 26
5.3.3.3 Interworking of Target MME with 3GPP MSC Server enhanced for SRVCC from CS to PS . 26
5.3.3A SGSN . 26
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5.3.3A.1 Interworking with 3GPP MSC Server enhanced for SRVCC from E-UTRAN / UTRAN (HSPA)
to 3GPP UTRAN/GERAN . 26
5.3.3A.1.1 Interworking with 3GPP MSC Server enhanced for SRVCC. 26
5.3.3A.1.2 PS bearer splitting function . 26
5.3.3A.1.3 Selection of MSC enhanced for SRVCC . 27
5.3.3A.2 Interworking of Target SGSN with 3GPP MSC Server enhanced for SRVCC from CS to PS . 27
5.3.4 UE enhanced for SRVCC . 27
5.3.4.1 Interworking with 3GPP2 1xCS . 27
5.3.4.2 Interworking with 3GPP UTRAN/GERAN for SRVCC from E-UTRAN / UTRAN (HSPA) to
3GPP UTRAN/GERAN . 27
5.3.4.3 Interworking of UE with 3GPP UTRAN/GERAN for SRVCC from CS to PS . 27
5.3.4a UE enhanced for vSRVCC . 27
5.3.5 Serving/PDN GW . 28
5.3.6 E-UTRAN . 28
5.3.6.1 Interworking with 3GPP2 1xCS . 28
5.3.6.2 Interworking with 3GPP UTRAN/GERAN for SRVCC from E-UTRAN to 3GPP
UTRAN/GERAN . 28
5.3.6.2a Interworking with 3GPP UTRAN for vSRVCC . 28
5.3.6A UTRAN (HSPA) . 28
5.3.6B GERAN/UTRAN CS . 29
5.3.7 HSS . 29
5.3.7.1 Interworking with 3GPP UTRAN/GERAN for SRVCC or vSRVCC from E-UTRAN / UTRAN
(HSPA) to 3GPP UTRAN/GERAN . 29
5.3.7.2 Interworking with 3GPP UTRAN/GERAN for SRVCC from CS to PS . 29
5.3.8 PCC . 29
5.4 Reference points . 30
5.4.1 MME – 3GPP2 1xCS IWS (S102) . 30
5.4.2 MME/SGSN – MSC Server (Sv) . 30
5.4.3 E-UTRAN – MME (S1-MME) . 30
5.4.3A UTRAN (HSPA) – SGSN (Iu-ps) . 30
5.4.4 HSS – MME (S6a) . 30
5.4.5 HSS – SGSN (Gr, S6d) . 30
5.4.6 HSS - MSC (MAP D) . 30
6 Procedures and flows. 31
6.1 SRVCC from E-UTRAN to 3GPP2 1xCS . 31
6.1.1 E-UTRAN Attach procedure for SRVCC . 31
6.1.2 Service Request procedures for SRVCC . 31
6.1.2A PS Handover procedures for SRVCC . 31
6.1.3 Call flows for SRVCC from E-UTRAN . 31
6.2 E-UTRAN and 3GPP GERAN/UTRAN (v)SRVCC . 34
6.2.1 E-UTRAN Attach procedure for (v)SRVCC . 34
6.2.1A Service Request procedures for (v)SRVCC . 34
6.2.1B PS Handover procedures for (v)SRVCC . 34
6.2.1C Dedicated Bearer Establishment and Modification procedures for vSRVCC . 35
6.2.2 Call flows for (v)SRVCC from E-UTRAN . 35
6.2.2.1 SRVCC from E-UTRAN to GERAN without DTM support . 35
6.2.2.1A SRVCC from E-UTRAN to GERAN with DTM but without DTM HO support and from E-
UTRAN to UTRAN without PS HO . 39
6.2.2.2 SRVCC from E-UTRAN to UTRAN with PS HO or GERAN with DTM HO support . 39
6.2.2.3 vSRVCC from E-UTRAN to UTRAN with PS HO support. 44
6.2.2.4 vSRVCC from E-UTRAN to UTRAN without PS HO support . 47
6.2.3 Returning back to E-UTRAN . 47
6.3 UTRAN (HSPA) and 3GPP GERAN/UTRAN SRVCC . 48
6.3.1 GPRS Attach procedure for SRVCC . 48
6.3.1A Service Request procedures for SRVCC . 48
6.3.1B PS Handover procedures for SRVCC . 48
6.3.2 Call flows for SRVCC from UTRAN (HSPA) . 49
6.3.2.1 SRVCC from UTRAN (HSPA) to GERAN without DTM support . 49
6.3.2.1A SRVCC from UTRAN (HSPA) to GERAN with DTM but without DTM HO support and from
UTRAN (HSPA) to UTRAN without PS HO . 52
6.3.2.2 SRVCC from UTRAN (HSPA) to UTRAN or GERAN with DTM HO support . 52
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6.4 CS to PS SRVCC . 56
6.4.1 GPRS Attach procedure for SRVCC . 56
6.4.2 E-UTRAN Attach procedure for SRVCC . 56
6.4.3 Call flows for SRVCC to E-UTRAN/UTRAN (HSPA) . 56
6.4.3.1 SRVCC to E-UTRAN/UTRAN (HSPA) from GERAN without DTM/PS HO support . 56
6.4.3.2 SRVCC to E-UTRAN/UTRAN (HSPA) from GERAN with DTM support but without DTM HO
support and SRVCC to E-UTRAN from UTRAN without PS HO support . 59
6.4.3.3 SRVCC to E-UTRAN/UTRAN (HSPA) with DTM/PS HO support . 59
7 Charging . 59
8 Handover Failure . 59
8.1 Failure in EUTRAN/UTRAN (HSPA) to 3GPP UTRAN/GERAN (v)SRVCC . 59
8.1.1 Failure before MSC Server initiates Session Transfer . 59
8.1.1a Failure after MSC Server initiates Session Transfer . 59
8.1.1a.1 Failure before responding to PS to CS HO request . 59
8.1.1a.2 Failure after responding to PS to CS HO request . 60
8.1.2 Failure after UE receives HO command . 61
8.1.3 Handover Cancellation . 61
8.1.4 Handover Failure due to alerting/pre-alerting state . 62
8.2 Failure in CS to PS SRVCC . 63
8.2.1 Failure before UE initiates Session Transfer detected by MSC Server . 63
8.2.2 Failure before UE initiates Session Transfer detected by MME . 63
8.2.3 CS to PS Handover Cancellation . 64
9 Security. 65
9.1 Network Domain Security with 3GPP2 1xCS IWS . 65
9.2 Network Domain Security with 3GPP UTRAN/GERAN MSC Server . 65
Annex A (informative): Determination of Neighbour Cell List . 66
A.1 SRVCC from E-UTRAN to 3GPP2 1xCS . 66
A.2 SRVCC from E-UTRAN to GERAN / UTRAN . 66
A.3 SRVCC from UTRAN (HSPA) to GERAN / UTRAN . 66
A.4 SRVCC from GERAN / UTRAN to E-UTRAN / UTRAN (HSPA) . 67
Annex B (informative): Change history . 68
History . 71

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Foreword
This Technical Specification has been produced by the 3rd 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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3GPP TS 23.216 version 15.3.0 Release 15 7 ETSI TS 123 216 V15.3.0 (2019-10)
1 Scope
This document specifies the architecture enhancements for Single Radio Voice Call Continuity (SRVCC) between the
following access systems for voice calls that are anchored in the IMS:
- from E-UTRAN to 3GPP2 1xCS;
- from E-UTRAN to UTRAN/GERAN;
- from UTRAN (HSPA) to UTRAN/GERAN.
- from UTRAN/GERAN to E-UTRAN.
- from GERAN to UTRAN (HSPA).
This document will not describe 3GPP2 functional entities. However, interfaces between both 3GPP and 3GPP2
functional entities are described in this specification.
SRVCC from E-UTRAN access to 3GPP2 1xCS is covered in this specification, including the handling of IMS
emergency call continuity. Handling of non-voice component and SRVCC from 3GPP2 1xCS to E-UTRAN direction is
not specified in this release.
SRVCC from E-UTRAN/UTRAN (HSPA) access and 3GPP UTRAN/GERAN CS accesses for voice calls that are
anchored in the IMS, as well as the coordination between the SRVCC for voice call and the handover of non-voice PS
bearers are covered in this specification. SRVCC with IMS emergency call continuity from E-UTRAN/UTRAN
(HSPA) to 3GPP UTRAN/GERAN CS accesses for voice calls is covered in this specification. SRVCC with eCall over
IMS continuity from E-UTRAN/UTRAN (HSPA) to 3GPP UTRAN/GERAN CS accesses is covered in this
specification. SRVCC with priority handling from E-UTRAN to 3GPP UTRAN/GERAN CS accesses for voice or
voice and video calls is also covered in this specification. The handover of non-voice PS bearer from E-UTRAN is
specified by the procedures defined in TS 23.401 [2], TS 23.060 [10], TS 25.413 [11] and TS 43.129 [12]. The
handover of non-voice PS bearer from UTRAN (HSPA) is specified by the procedures defined in TS 23.060 [10],
TS 25.413 [11] and TS 43.129 [12].
This document specifies the architecture enhancements for Single Radio Video Call Continuity (vSRVCC) from E-
UTRAN to UTRAN-CS access for Video Calls that are anchored in the IMS.
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 23.401: "GPRS enhancements for E-UTRAN access".
[3] 3GPP TS 23.402: "Architecture enhancements for non-3GPP accesses".
[4] 3GPP2 X.S0042-0: "Voice Call Continuity between IMS and Circuit Switched System".
[5] Void.
[6] Void.
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[7] 3GPP TR 36.938: "Improved Network Controlled Mobility between E-UTRAN and
3GPP2/Mobile WiMAX Radio Technologies".
[8] 3GPP2 A.S0008-C: "Interoperability Specification (IOS) for High Rate Packet Data (HRPD)
Radio Access Network Interfaces with Session Control in the Access Network".
[9] 3GPP TS 22.278: "Service requirements for the Evolved Packet System (EPS)".
[10] 3GPP TS 23.060: "General Packet Radio Service (GPRS); Service description; Stage 2".
[11] 3GPP TS 25.413: "UTRAN Iu interface Radio Access Network Application Part (RANAP)
signalling".
[12] 3GPP TS 43.129: "Packet-switched handover for GERAN A/Gb mode; Stage 2".
[13] 3GPP TS 23.292: "IP Multimedia Subsystem (IMS) Centralized Services: Stage 2".
[14] 3GPP TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity: Stage 2".
[15] 3GPP TS 23.002: "Network Architecture".
[16] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2".
[17] Void.
[18] 3GPP TS 23.009: "Handover procedures".
[19] 3GPP TS 25.331: "Radio Resource Control (RRC) protocol specification".
[20] 3GPP2 A.S0014: "Interoperability Specification (IOS) for cdma2000 Access Network Interfaces".
[21] 3GPP TS 33.210: "3G Security; Network Domain Security; IP network layer security".
[22] 3GPP TS 33.401: "3GPP System Architecture Evolution (SAE): Security architecture".
[23] 3GPP TS 48.008: "Mobile Switching Centre - Base Station System (MSC-BSS) interface; Layer 3
specification".
[24] 3GPP TS 48.018: "General Packet Radio Service (GPRS); Base Station System (BSS) - Serving
GPRS Support Node (SGSN); BSS GPRS Protocol (BSSGP)".
[25] 3GPP TS 33.102: "3G Security; Security architecture".
[26] 3GPP TS 22.173: "IP Multimedia Core Network Subsystem (IMS) Multimedia Telephony Service
and supplementary services".
[27] 3GPP TS 23.003: "Numbering, addressing and identification".
[28] 3GPP TS 23.167: "IP Multimedia Core Network Subsystem (IMS) emergency sessions".
[29] 3GPP TS 23.271: "Functional stage 2 description of Location Services (LCS)".
[30] 3GPP TS 36.413: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1
Application Protocol (S1AP)".
[31] 3GPP TS 22.101: "Service aspects; Service principles".
[32] 3GPP TS 23.203: "Policy and charging control architecture".
[33] ITU-T Recommendation H.324 Annex K: "Media oriented negotiation acceleration procedure"
and associated changes to Annex J".
[34] 3GPP TS 26.111: "Codec for circuit switched multimedia telephony service; Modifications to
H.324".
[35] 3GPP TR 26.911: "Codec(s) for Circuit-Switched (CS) multimedia telephony service; Terminal
implementor's guide".
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[36] 3GPP TS 36.423: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2
Application Protocol (X2AP)".
[37] 3GPP TS 29.303: "Domain Name System Procedures; Stage 3".
[38] 3GPP TS 22.002: "Circuit Bearer Services (BS) supported by a Public Land Mobile Network
(PLMN)".
[39] 3GPP TS 22.003: "Circuit Teleservices supported by a Public Land Mobile Network (PLMN)".
[40] 3GPP TS 23.251: "Network sharing; Architecture and functional description".
[41] 3GPP TS 29.002: "Mobile Application Part (MAP) specification".
[42] 3GPP TS 23.272: "Circuit Switched (CS) fallback in Evolved Packet System (EPS)".
[43] 3GPP TS 26.267: "eCall data transfer; In-band modem solution; General description".
[44] 3GPP TS 24.008: "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3".
[45] 3GPP TS 23.502: "Procedures for the 5G System".
[46] Void.
[47] Void.
[48] TS 23.501: "System architecture for the 5G System (5GS)".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions given in TR 21.905 [1] and the following apply. A
term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
1xCS: The 3GPP2 legacy circuit switched signalling system as defined in 3GPP2 X.S0042-0 [4].
3GPP SRVCC UE: A 3GPP SRVCC UE is a UE enhanced for IMS Service Continuity with the additional UE
capabilities described in this specification for SRVCC between E-UTRAN and 3GPP UTRAN and / or between E-
UTRAN and 3GPP GERAN and / or between UTRAN (HSPA) and 3GPP UTRAN and 3GPP GERAN.
Correlation MSISDN: An MSISDN used for correlation of sessions. See TS 23.003 [27] for more information.
Emergency Session Transfer Number for SRVCC (E-STN-SR): see TS 23.237 [14].
IMS-based MPS Session: see TS 23.401 [2].
Session Transfer Number for SRVCC (STN-SR): see TS 23.237 [14].
Single Radio Voice Call Continuity (SRVCC): Voice call continuity between IMS over PS access and CS access for
calls that are anchored in IMS when the UE is capable of transmitting/receiving on only one of those access networks at
a given time.
Single Radio Video Call Continuity (vSRVCC): Video call continuity from E-UTRAN to UTRAN-CS for calls that
are anchored in the IMS when the UE is capable of transmitting/receiving on only one of those access networks at a
given time. In this specification, the term vSRVCC is introduced for Single Radio Video Call Continuity to differentiate
it from Single Radio Voice Call Continuity (SRVCC).
CS to PS Single Radio Voice Call Continuity (CS to PS SRVCC): SRVCC from UTRAN to E-UTRAN, and
SRVCC from GERAN to UTRAN/E-UTRAN.
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Video Call: For IMS over E-UTRAN, it represents the session using bidirectional voice and synchronised real time
video as specified in TS 22.173 [26]. For UTRAN-CS, it represents the Circuit Switched (CS) multimedia calls as
specified in TS 22.101 [31].
For the purposes of the present document, the following terms and definitions given in TS 23.401 [2] apply:
eCall Only Mode: See TS 23.401 [2].
For the purposes of the present document, the following terms and definitions given in TS 22.101 [31] apply:
eCall: See TS 22.101 [31].
Minimum Set of Data (MSD): See TS 22.101 [31].
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
1xCS IWS Single Radio Voice Call Continuity Interworking solution Function for 3GPP2 1xCS
ARP Allocation and Retention Priority
C-MSISDN Correlation MSISDN
MPS Multimedia Priority Service
MSD Minimum Set of emergency related Data
SAI Service Area Identifier as defined in TS 25.413 [11] and TS 23.003 [27]
SRVCC Single Radio Voice Call Continuity
vSRVCC Single Radio Video Call Continuity

4 High level Principles and Concepts
4.1 High level Principles
4.1.1 Architectural Principles for 3GPP2 1xCS SRVCC
The solution for SRVCC fulfils the requirements of TS 22.278 [9] and the following architectural principles:
1. The solution shall allow coexistence and be compatible with the 1xCS procedures specified in the 3GPP2 VCC
specification, X.S0042 [4].
2. The solution shall not require UE with multiple RATs capability to simultaneously signal on two different RATs.
3. The solution shall be transparent to E-UTRA only terminal or network.
4. The solution shall minimize the coupling between the E-UTRAN and the 3GPP2 access. In particular, the
solution shall allow the cdma2000 1xRTT specification to evolve without necessitating a modification to the E-
UTRAN specifications.
5. RAT change and domain selection should be under network control.
6. In roaming cases, the Visited PLMN should control the RAT change and/or domain selection while taking into
account any related HPLMN policies.
7. The solution shall not impact cdma2000 RAT.
8. The solution shall not impact cdma2000 CS CN.
9 All IMS sessions that may be subject to SRVCC shall be anchored in the IMS (VCC Application).
10. When SRVCC is deployed, QCI=1:
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- shall not be used for IMS sessions that are not anchored in the IMS (VCC Application); and
- shall only be used for the voice bearer.
4.1.2 Architectural Principles for SRVCC and vSRVCC to 3GPP
UTRAN/GERAN
The solution for (v)SRVCC fulfils the requirements of TS 22.278 [9] and the following architectural principles:
1. The solution shall allow coexistence and be compatible with TS 23.292 [13] and TS 23.237 [14].
2. The solution shall not require UE with multiple RATs capability to simultaneously signal on two different RATs.
3. RAT change and domain selection should be under network control.
4. E-UTRAN/UTRAN (HSPA) to UTRAN/GERAN CS handover for SRVCC is triggered by the same radio
handover conditions and mechanisms as for an E-UTRAN/UTRAN (HSPA) to UTRAN/GERAN PS handover.
5. The Video Call by IMS over E-UTRAN is the IMS session with bi-directional video and voice media e.g. IMS
Multimedia Telephony as defined in TS 22.173 [26] which uses separate EPS bearers for video and voice
components, respectively.
6. In roaming cases, the VPLMN shall be able to control the RAT/domain selection change while taking into
account any related HPLMN policies for IMS sessions with bi-directional video and voice media e.g. IMS
Multimedia Telephony as defined in TS 22.173 [26].
7 All IMS sessions that may be subject to (v)SRVCC shall be anchored in the IMS (SCC AS).
8. When SRVCC is deployed, QCI=1 / traffic-class 'Conversational' with Source Statistics Descriptor ='speech':
- shall not be used for IMS sessions that are not anchored in the IMS (SCC AS); and
- shall only be used for the voice bearer.
NOTE 1: The UE may have multiple voice media streams that are multiplexed over a single voice (e.g. QCI=1)
bearer. Selection of the voice streams for SRVCC by the SCC AS is as specified in TS 23.237 [14].
NOTE 2: The UE may have multiple voice and video media streams that are carried over a single voice but
multiple video (QCI=1 and the vSRVCC marked bearer) bearers or are multiplexed each over a single
media bearer. Only one of these voice or voice and video streams is selected for SRVCC or vSRVCC by
the SCC AS (see TS 23.237 [14]).
4.1.3 Architectural Principles for SRVCC to 3GPP E-UTRAN/UTRAN
(HSPA)
The solution for CS to PS SRVCC fulfils the following architectural principles in addition to the ones defined in
clause 4.1.2:
- A CS to PS SRVCC procedure shall be possible for CS call that is originated from UTRAN/GERAN.
- After transfer from CS to PS SRVCC, it shall support moving the session back to UTRAN/GERAN CS domain
if SRVCC from E-UTRAN/HSPA PS-domain is supported.
- A CS to PS SRVCC procedure shall be possible after SRVCC from E-UTRAN/HSPA PS-domain to CS domain
has occurred.
- Emergency session is not subjected to CS to PS SRVCC procedure.
A prerequisite for the CS to PS SRVCC procedure to take place is that the UE is registered in IMS and has at least one
PS bearer (usable for SIP signalling).
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4.2 Concepts
4.2.1 E-UTRAN to 3GPP2 1xCS SRVCC
For SRVCC-capable UEs, the call is always anchored at the VCC AS in the 3GPP2's IMS. The 3GPP2 1xCS IWS
enables a single radio UE to communicate in parallel both with the source system and the target system. From VCC
perspective, this mechanism minimizes the voice gap by supporting the transport of signalling for establishment of the
target CS access leg while the terminal is connected to the source PS access network.

Figure 4.2.1-1: Transport of 3GPP2 1xCS signalling messages for preparation of the CS access leg in
the target system
The S102 reference point is used to convey 3GPP2 1xCS signalling messages between the MME and 3GPP2 1xCS
IWS. These 1x CS signalling messages are actually exchanged between the UE and the 3GPP2 1xCS IWS, and S102 is
only one link in the overall UE-1xCS IWS tunnelling path. On the remaining portion of the tunnelling path, the 3GPP2
1xCS signalling messages are encapsulated in E-UTRAN/EPS tunnelling messages (UE-MME).
4.2.2 E-UTRAN to 3GPP UTRAN/GERAN SRVCC
For facilitating session transfer (SRVCC) of the voice component to the CS domain, the IMS multimedia telephony
sessions needs to be anchored in the IMS.
For SRVCC from E-UTRAN to UTRAN/GERAN, MME first receives the handover request from E-UTRAN with the
indication that this is for SRVCC handling, and then triggers the SRVCC procedure with the MSC Server enhanced for
SRVCC via the Sv reference point if MME has STN-SR information for this UE. If SRVCC with priority is supported,
based on the ARP associated with the EPS bearer used for IMS signalling, the MME sets the priority indication
appropriately toward the MSC Server. MME aware of which EPS bearer is used for IMS signalling based on local
configuration. MSC Server enhanced for SRVCC then initiates the session transfer procedure to IMS and coordinates it
with the CS handover procedure to the target cell. If SRVCC with priority is supported, IMS session transfer procedure
and the CS handover procedure are performed with priority handling per the priority indication received from MME.
MSC Server enhanced for SRVCC then sends PS-CS handover Response to MME, which includes the necessary CS
HO command information for the UE to access the UTRAN/GERAN.
Handling of any non-voice PS bearer is done by the PS bearer splitting function in the MME. MME starts the handover
of non-voice PS bearer during SRVCC procedure based on the information received from E-UTRAN. The handover of
non-voice PS bearer(s), if performed, is done as according to Inter RAT handover procedure as defined in
TS 23.401 [2]. The MME is responsible to coordinate the Forward Relocation Response from PS-PS handover
procedure and the SRVCC PS to CS Response.
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Target
UE E - UTRAN MME MSC Server 3 GPP IMS
UTRAN / GERAN
Measurement
Reports
Handover to UTRAN / GERAN
required
Initiates SRVCC for voice component
CS handover preparation
Handles PS - PS HO for
non - voice if needed   IMS Service Continuity Procedure
To eUTRAN
C S HO response to MME
Coordinates SRVCC
( CS resources )
Handover CMD
and PS HO response
Handover
execution
Figure 4.2.2-1: Overall high level concepts for SRVCC from E-UTRAN to UTRAN/GERAN
4.2.2a E-UTRAN to 3GPP UTRAN vSRVCC
For facilitating session transfer of the voice and video components to the CS domain, the IMS multimedia telephony
sessions needs to be anchored in the IMS.
For vSRVCC, the UE uses one voice and one video media component
...