Content for TR 33.856 Word version: 16.1.0
0 Introduction
1 Scope
2 References
3 Definitions and abbreviations
3.1 Definitions
3.2 Abbreviations
4 Overview
...
...
0 Introduction p. 5
The interworking between NR and UTRAN is not supported in 3GPP, leading to the lack of Voice Call Continuity from NR to UTRAN. This may cause problem to voice service, when NR coverage is limited, as listed below:
Scenario # - Operators with both VoNR and VoLTE enabled:
- In the initial stage of 5G deployment, the voice service continuity may not be guaranteed if the VoLTE coverage provided by the operators is not (ideal) complete, i.e., there are some "holes" of VoLTE coverage.
1 Scope p. 6
The present document studies the security aspects of single radio voice continuity from 5G to UTRAN CS. In particular, the goal of the present document is to study the impacts on 3GPP security architecture which may result from 5GS to UTRAN CS voice continuity, e.g. security context mapping from 5G and UTRAN, security procedure for the emergency call, etc.
2 References p. 6
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] TS 33.501: "Security architecture and procedures for 5G system".
[2] TR 23.756: Study for single radio voice continuity from 5G to 3G".
[3] TR 21.905: "Vocabulary for 3GPP Specifications".
[4] TS 33.401: "3GPP System Architecture Evolution (SAE); Security architecture".
[5] TS 23.216: "Single Radio Voice Call Continuity (SRVCC)".
3 Definitions and abbreviations p. 6
3.1 Definitions p. 6
For the purposes of the present document, the terms and definitions given in TR 21.905 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.
3.2 Abbreviations p. 6
For the purposes of the present document, the abbreviations given in TR 21.905 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.
AMF
Access and Mobility Management Function
CS
Circuit Switched
EPS
Evolved Packet System
E-UTRAN
Evolved UTRAN
HO
HandOver
IMS
IP Multimedia Subsystem
MSC
Mobile Switching Center
NAS
Non Access Stratum
NR
New Radio
PS
Packet Switched
SRVCC
Single Radio Voice Call Continuity
UE
User Equipment
UMTS
Universal Mobile Telecommunications System
UTRAN
Universal Terrestrial Radio Access Network
4 Overview p. 6
The interworking between NR and UTRAN is not supported in 3GPP, leading to the lack of Voice Call Continuity from NR to UTRAN. This may cause problem to voice service, have impact on the user experience, when NR coverage is limited, as listed below:
Scenario #1 - Operator with both VoNR and VoLTE enabled
- In the initial stage of 5G deployment, the voice service continuity may not be guaranteed if the VoLTE coverage provided by the operators is not (ideal) complete, i.e., there are some "holes" of VoLTE coverage.
- Some operators deploys VoNR and LTE, but do not launch VoLTE in their LTE network, which means VoNR will be dropped if the UE moves from 5G coverage to LTE coverage.
- In some countries, the operators only have GSM/UTRAN deployment currently. Deploying 5G system and VoNR directly would be infeasible for them since the voice continuity cannot be guaranteed. Thus the voice service continuity from 5G to UTRAN is supported for MNOs that are in one of the above scenarios, in order to enable such an MNO to offer a good service to its subscribers.
