ETSI TS 123 632 V17.3.0 (2022-10)

LTE; 5G; User data interworking, coexistence and migration; Stage 2 (3GPP TS 23.632 version 17.3.0 Release 17)

RTS/TSGC-0423632vh30

General Information

• Status: Not Published
• Technical Committee: 3GPP CT 4 - MAP/CAMEL/GTP/BCH/SS/TrFO/IMS/GUP/WLAN (formely CN4)
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 04-Oct-2022

Standards Content (Sample)

TECHNICAL SPECIFICATION
LTE;
5G;
User data interworking, coexistence and migration;
Stage 2
(3GPP TS 23.632 version 17.3.0 Release 17)

3GPP TS 23.632 version 17.3.0 Release 17 1 ETSI TS 123 632 V17.3.0 (2022-10)

Reference
RTS/TSGC-0423632vh30
Keywords
5G,LTE
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ETSI
3GPP TS 23.632 version 17.3.0 Release 17 2 ETSI TS 123 632 V17.3.0 (2022-10)
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Legal Notice
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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
3GPP TS 23.632 version 17.3.0 Release 17 3 ETSI TS 123 632 V17.3.0 (2022-10)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 7
2 References . 7
3 Definitions of terms, symbols and abbreviations . 8
3.1 Terms . 8
3.2 Symbols . 8
3.3 Abbreviations . 8
4 System architecture . 8
4.1 Architecture for direct UDM-HSS interworking . 8
4.2 Reference points for direct UDM-HSS interworking . 9
4.3 Service based interfaces for direct UDM-HSS interworking . 9
4.4 Subscription Identifiers . 10
4.5 HSS Discovery and Selection . 10
4.6 UDM Discovery and Selection . 10
4.7 Subscription Profiles . 10
5 System procedures . 11
5.1 General . 11
5.2 Authentication . 11
5.2.1 General . 11
5.2.2 Vector Generation in HSS . 11
5.2.3 Vector Generation in UDM/ARPF . 12
5.2.4 HSS using the Nudr SBI . 14
5.3 5GC-EPC Mobility Scenarios . 14
5.3.1 General . 14
5.3.2 Mobility from 5GC to EPC . 15
5.3.3 Mobility from EPC to 5GC . 16
5.3.4 Support for PDU session continuity during intersystem mobility procedures . 17
5.4 Scenarios of Interworking with IMS . 22
5.4.1 T-ADS . 22
5.4.2 P-CSCF Restoration . 24
5.4.3 Network Provided Location Information Request . 25
5.4.4 User State Retrieval . 26
5.4.5 UE Reachability . 27
5.4.6 IMEI Retrieval . 30
5.4.7 SRVCC: IMS AS obtaining SRVCC data . 31
5.4.8 SRVCC: IMS AS obtaining SRVCC data – HSS using Nudr . 31
5.4.9 SRVCC: IMS AS updating STN-SR . 32
5.5 SMS Support . 33
5.5.1 General . 33
5.5.2 MT-SMS Routing Information Retrieval . 33
5.5.3 MT-SMS Delivery Failure . 34
5.5.4 SMS Alerting . 36
5.5.5 MT-SMS Routing Information Retrieval Over Nudr . 37
5.5.6 Support for SMS over IP . 37
5.5.6.1 General . 37
5.5.6.2 IP-SM-GW registration and SMS routing information retrieval in 5GC only deployments . 37
5.5.6.3 MT SMS delivery failure in 5GC only deployments . 39
5.5.6.4 Alert Service Centre in 5GC only deployments . 40
5.6 Common Network Exposure Scenarios . 41
5.6.1 General . 41
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5.6.2 Configuration of Monitoring Events in MME . 42
5.6.3 Synchronization of Status of Monitoring Event between HSS and UDM . 43
6 Network Function Service procedures . 45
6.1 HSS Services . 45
6.1.1 General . 45
6.1.2 Nhss_UEAuthentication service . 45
6.1.2.1 Nhss_UEAuthentication_Get service operation . 45
6.1.3 Nhss_UECM service. 45
6.1.3.1 Nhss_UECM_SNDeregistration service operation . 45
6.1.3.2 Nhss_UECM_Update service operation . 46
6.1.4 Nhss_SDM service . 46
6.1.4.1 Nhss_SDM_Get service operation . 46
6.1.4.2 Nhss_SDM_Notification service operation . 46
6.1.4.3 Nhss_SDM_Subscribe service operation . 46
6.1.4.4 Nhss_SDM_Unsubscribe service operation . 47
6.1.5 Nhss_EE service . 47
6.1.5.1 Nhss_EE_Subscribe service operation . 47
6.1.5.2 Nhss_EE_Unsubscribe service operation . 47
6.1.5.3 Nhss_EE_Notify service operation . 47
6.2 UDM Services . 48
6.2.1 General . 48
6.2.2 Nudm_UECM service operation . 48
6.2.2.1 Nudm_UECM_P-CscfRestorationTrigger service operation . 48
6.2.2.2 Nudm_UECM_Get service operation . 48
6.2.2.3 Nudm_UECM_AMFDeregistration service operation . 48
6.2.2.4 Nudm_UECM_Update service operation . 49
6.2.3 Nudm_MT Service . 49
6.2.3.1 Nudm_MT_ProvideDomainSelectionInfo Service . 49
6.2.3.2 Nudm_MT_ProvideUserState service operation . 49
6.2.3.3 Nudm_MT_ProvideLocationInfo service operation . 49
6.2.3.4 Nudm_MT_Provide5GSRVCCInfo Operation . 49
6.2.4 Nudm_EE Service . 50
6.2.4.1 Nudm_EventExposure_Subscribe service operation . 50
6.2.4.2 Nudm_EventExposure_Notify service operation . 50
6.2.5 Nudm_UEAuthentication service . 50
6.2.5.1 Nudm_UEAuthentication_GetHssAv service operation . 50
6.2.6 Nudm_SDM service operations . 50
6.2.6.1 Nudm_SDM_Get service operation . 50
6.2.6.2 Nudm_SDM_Subscribe service operation . 50
6.2.6.3 Nudm_SDM_Unsubscribe service operation . 50
6.2.6.4 Nudm_SDM_Notify service operation . 50
6.2.7 Nudm_PP service operations . 51
6.2.7.1 Nudm_PP_Update service operation. 51
6.3 UDR Services . 51
Annex A (informative): Change history . 52
History . 53

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3GPP TS 23.632 version 17.3.0 Release 17 5 ETSI TS 123 632 V17.3.0 (2022-10)
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.
In the present document, modal verbs have the following meanings:
shall indicates a mandatory requirement to do something
shall not indicates an interdiction (prohibition) to do something
The constructions "shall" and "shall not" are confined to the context of normative provisions, and do not appear in
Technical Reports.
The constructions "must" and "must not" are not used as substitutes for "shall" and "shall not". Their use is avoided
insofar as possible, and they are not used in a normative context except in a direct citation from an external, referenced,
non-3GPP document, or so as to maintain continuity of style when extending or modifying the provisions of such a
referenced document.
should indicates a recommendation to do something
should not indicates a recommendation not to do something
may indicates permission to do something
need not indicates permission not to do something
The construction "may not" is ambiguous and is not used in normative elements. The unambiguous constructions
"might not" or "shall not" are used instead, depending upon the meaning intended.
can indicates that something is possible
cannot indicates that something is impossible
The constructions "can" and "cannot" are not substitutes for "may" and "need not".
will indicates that something is certain or expected to happen as a result of action taken by an agency
the behaviour of which is outside the scope of the present document
will not indicates that something is certain or expected not to happen as a result of action taken by an
agency the behaviour of which is outside the scope of the present document
might indicates a likelihood that something will happen as a result of action taken by some agency the
behaviour of which is outside the scope of the present document
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might not indicates a likelihood that something will not happen as a result of action taken by some agency
the behaviour of which is outside the scope of the present document
In addition:
is (or any other verb in the indicative mood) indicates a statement of fact
is not (or any other negative verb in the indicative mood) indicates a statement of fact
The constructions "is" and "is not" do not indicate requirements.

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1 Scope
The present document defines the Stage 2 architecture, procedures, flows and Network Function Services for User Data
Interworking, Coexistence and Migration within the 5G System.
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 23.501: "System Architecture for the 5G System; Stage 2".
[3] 3GPP TS 23.002: "Network Architecture".
[4] 3GPP TS 23.380: "IMS Restoration Procedures".
[5] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[6] 3GPP TS 33.501: "Security Architecture and Procedures for 5G System".
[7] 3GPP TS 23.228: "IP Multimedia Subsystem (IMS); Stage 2".
[8] 3GPP TS 33.401: "3GPP System Architecture Evolution (SAE); Security architecture".
[9] 3GPP TS 33.402: "3GPP System Architecture Evolution (SAE); Security aspects of non-3GPP
accesses".
[10] 3GPP TS 33.203: "3G security; Access security for IP-based services".
[11] 3GPP TS 33.220: "3G security; Generic Authentication Architecture (GAA); Generic
Bootstrapping Architecture (GBA)".
[12] 3GPP TS 24.080: "Mobile radio interface layer 3 supplementary services specification - Formats
and coding".
[13] 3GPP TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity".
[14] 3GPP TS 23.008: "Organization of subscriber data".
[15] 3GPP TS 29.328: "IP Multimedia (IM) Subsystem Sh interface; Signalling flows and message
contents".
[16] 3GPP TS 23.682: "Architecture enhancements to facilitate communications with packet data
networks and applications; Stage 2".
[17] 3GPP TS 23.040: "Technical realization of the Short Message Service (SMS)".
[18] 3GPP TS 23.204: "Support of Short Message Service (SMS) over generic 3GPP Internet Protocol
(IP) access; Stage 2".
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3 Definitions of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in 3GPP 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 3GPP TR 21.905 [1].
3.2 Symbols
Void
3.3 Abbreviations
For the purposes of the present document, the abbreviations given in 3GPP 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
3GPP TR 21.905 [1].
5GS UDR 5G Unified Data Repository
EPS UDR EPS User Data Repository
4 System architecture
4.1 Architecture for direct UDM-HSS interworking
Figure 4.1-1 shows the reference architecture for direct UDM-HSS interworking.
NF UDM
NF NF
Nudm
other 5GC SBA interfaces Nudr
Nhss
5GS-UDR
Ud
EPS-UDR
HSS
IMS SBA interfaces Non-SBA interfaces
SBA IMS non-SBA
network network
nodes nodes
Figure 4.1-1: Architecture for Direct UDM-HSS interworking
Non-SBA interfaces between the HSS and non-SBA network nodes include interfaces to / from the SMS-
GMSC/IWMSC and SMS Router. In the Architecture for direct UDM-HSS interworking , as a deployment option, these
Non-SBA interfaces may either be supported by the HSS or by the UDM.
Figure 4.1-2 shows the reference architecture for direct UDM-HSS interworking using the reference point
representation.
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EPS-UDR
5GS-UDR
N35 NU2
Ud
NU1
UDM HSS
S6a/S6d/ Cx/Sh
N8/N10/N13/
N21/N52/NL6 SWx/. N70/N71
N26
5GC EPC IMS
Figure 4.1-2: Architecture for Direct UDM-HSS interworking in reference point representation
The 5GS-UDR (Unified Data Repository) and EPS-UDR (User Data Repository) may be collocated, forming a common
repository.
NOTE: The HSS is only using the NU2 reference point for the purpose of interworking with 5GS, i.e. NU2 is not
a replacement of the Ud interface.
4.2 Reference points for direct UDM-HSS interworking
The following reference points are realized by service-based interfaces:
NU1: Reference point between the HSS and the UDM.
NU2: Reference point between the HSS and the 5GS-UDR.
For a list of other SBA reference points supported in 5GC see 3GPP TS 23.501 [2].
For a list of IMS reference points, including SBA IMS reference points, see 3GPP TS 23.228 [7].
For a list of Non-SBA reference points and Network Nodes interfacing the HSS see 3GPP TS 23.002 [3].
The HSS makes use of the Ud reference point to interact with the EPS-UDR. The UDM makes use of the N35 reference
point to interact with the 5GS-UDR.
4.3 Service based interfaces for direct UDM-HSS interworking
Nudm: Service-based interface exhibited by UDM.
Nhss: Service-based interface exhibited by HSS.
The HSS shall make use of Nudm services as described in clause 6.2 and may make use of Nudr services as described
in clause 6.3.
The UDM shall make use of Nhss services and Nudr services as described in clauses 6.1 and 6.3.
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4.4 Subscription Identifiers
As defined in 3GPP TS 23.501 [2], for interworking with the EPC, the SUPI allocated to the 3GPP UE shall always be
based on an IMSI to enable the UE to present an IMSI to the EPC.
The subscription identifier used over NU1 reference point in Nhss services shall be an IMSI. The UDM extracts the
IMSI from the user's SUPI.
The subscription identifier used over NU1 reference point in Nudm services shall be a SUPI based on an IMSI. The
HSS creates a SUPI from the user's IMSI or the IMSI associated to the user's public identifier in the EPS or IMS
domain (e.g. user's MSISDN or IMPU).
4.5 HSS Discovery and Selection
This clause defines the procedures for HSS discovery and selection by the UDM. The procedures for HSS discovery
and selection by SBI capable IMS entities is defined in 3GPP TS 23.228 [7].
The UDM performs HSS discovery to discover an HSS that manages the user subscriptions in EPC.
The UDM shall utilize the NRF to discover the HSS instance(s) unless the information about HSS instances is available
by other means, e.g. locally configured on the UDM. The HSS selection function in UDM selects an HSS instance
based on the available HSS instances (obtained from the NRF or locally configured).
When the NRF is used for HSS discovery, the HSS registers in the NRF using the Nnrf_NFManagement_NFRegister
Request message as defined in 3GPP TS 23.502 [5].
Different HSS instances managing different sets of IMSI/MSISDN ranges may be deployed in a given PLMN. In this
case, the HSS instances register in NRF using either different ranges of IMSI/MSISDN and/or HSS Group IDs.
NOTE 1: In deployments where simple IMSI/MSISDN ranges are not suitable to describe the IMSI/MSISDN sets
served by HSS instances, it is expected the HSS instances only register HSS Group IDs.
When NRF is used for HSS discovery, the UDM sends a Nnrf_NFDiscovery_Request to NRF as defined in
3GPP TS 23.502 [5] to discover HSS instances within a given PLMN. The UDM may store all returned HSS instances
and their NF profiles for subsequent use, including, if applicable, supported IMSI/MSISDN ranges, and/or HSS Group
IDs.
The UDM may use Nnrf_NFStatusSubscribe/Unsubscribe service operations with NRF as defined in
3GPP TS 23.502 [5] to receive Nnrf_NFStatusNotify service operation for updates to the NF profiles of HSS instances
registered in NRF.
The UDM always selects an HSS within its own PLMN. The HSS selection should consider one of the following
factors when available to the UDM entity:
1. HSS Group ID of the UE's IMSI.
2. IMSI; the UDM selects an HSS instance based on the IMSI range the UE's IMSI belongs to or based on the
results of a discovery procedure with NRF using the UE's IMSI as input for HSS discovery.
NOTE 2: In this release of the specification there is not identified need for the UDM to be able to select the HSS
based on IMS identifiers (IMPI, IMPU) neither based on MSISDN or External Group ID.
4.6 UDM Discovery and Selection
The HSS performs UDM discovery and selection as described in 3GPP TS 23.501 [2].
4.7 Subscription Profiles
In the context of Mobility, IMS and SMS use cases, the HSS initiates interworking with the UDM only for UEs which
have a 5G subscription that is known to be active in 5GC.
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NOTE: The HSS may be aware that a 5G subscription for the UE exists based on the Core Network Type
restrictions defined for the UE (i.e. If restriction for Core Network Type indicates that the UE can access
to 5GC, it implies that the UE has 5G subscription data).
Additionally, the HSS may be aware that a UE for which 5G subscription data exist is not active in 5GC
e.g. when the HSS has not yet received an Nhss_UECM_ SNDeregistration request from the UDM for
that UE (see clause 5.3.3 step 3).
5 System procedures
5.1 General
Procedures involving communication between HSS and UDM comprise Authentication, Mobilty, IMS interworking,
and SMS support.
5.2 Authentication
5.2.1 General
A subscriber's authentication subscription data, including the subscriber's long-term key(s) and sequence number, shall
be stored in a single repository so that a single sequence number can be maintained for the subscriber.
The subscriber's long-term key(s) shall not be transferred over the NU1 reference point between HSS and UDM. Also it
is not expected that the UDM has direct standardized access to the EPS-UDR. Therefore, the following options exist for
subscribers with both 5G and EPS subscription:
1) Authentication subscription data are stored in the EPS-UDR and all authentication vectors are calculated in the HSS.
Subscription data stored in the 5GS-UDR or locally configured in the UDM indicate that the UDM needs to consume
the Nhss_UEAuthentication_Get service operation to retrieve a 5G vector from the HSS. See clause 5.2.2 for details.
2) Authentication subscription data are stored in the 5GS-UDR and all authentication vectors are calculated in the
UDM. Subscription data stored in the EPS-UDR or locally configured in the HSS indicate that the HSS needs to
consume the Nudm_UEAuthentication_GetHssAv service operation to retrieve an EPS vector from the UDM. See
clause 5.2.3 for details.
3) Authentication subscription data are stored in the 5GS-UDR, 5G vectors are calculated in the UDM and EPS vectors
are calculated in the HSS. Subscription data stored in the EPS-UDR or locally configured in the HSS indicate that the
HSS needs to consume the Nudr_DM_Query service operation to retrieve authentication subscription data from the
5GS-UDR. See clause 5.2.4 for details.
The following clauses specify the system procedures for these different alternatives.
5.2.2 Vector Generation in HSS
This clause specifies the procedures for authentication vector request when the subscriber's authentication subscription
data is stored at the EPS-UDR. In this case, the UDM requests the generation of the Authentication Vector for 5GS to
the HSS.
NOTE: The HSS acts as ARPF rather than as AuC and it is required to generate authentication vectors as defined
in 3GPP TS 33.501 [6].
When the UDM receives an authentication information Request from the AUSF it shall check (by means of an 5GS-
UDR query or local configuration in the UDM) whether the subscribed authentication method is 5G_AKA or
EAP_AKA_PRIME and if so whether 5G authentication vector generation for the identified subscriber shall be done in
the HSS. If so, the UDM shall make use of the Nhss_UEAuthentication_Get service operation to retrieve a 5G
authentication vector from the HSS.
Figure 5.2.2-1 shows the scenario where the authentication vector request for a 5G subscriber who also has an EPS
subscription is received by the UDM.
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Figure 5.2.2-1: Authentication for 5G subscriber with authentication vector generation in HSS
1. The UDM receives an Authentication Vector request, containing the identity of the user (SUPI or SUCI). If
SUCI is received, the UDM performs SUCI to SUPI de-concealment. For details of the
Nudm_UEAuthentication Service see 3GPP TS 23.502 [5] and 3GPP TS 33.501 [6].
2. If the 5GS-UDR is used, the UDM queries the 5GS-UDR using the SUPI to retrieve Authentication Subscription
Information. In this scenario the Authentication Subscription Information contains a subscribed authentication
method of 5G_AKA or EAP_AKA_PRIME and an indicator indicating that authentication vector generation
shall be performed in the HSS. Optionally, the indication that the authentication vector generation shall be
performed in the HSS could be locally configured at the UDM/ARPF.
3. The UDM uses the Nhss_UEAuthentication_Get service operation to retrieve an authentication vector from the
HSS. The request contains the IMSI the authentication method and serving network name.
4. The HSS reads authentication subscription data from the EPS-UDR. This step is omitted if all relevant
authentication subscription data are stored locally in the HSS.
5. The HSS (AuC/ARPF) calculates the requested authentication vector taking into account the serving network
name and authentication method received in step 3 and the authentication subscription information retrieved
from the EPS-UDR.
6. The calculated authentication vector is sent to the UDM.
7. The HSS updates the EPS-UDR with the new sequence number. This step is omitted if the sequence number is
stored locally in the HSS.
8. The UDM forwards the authentication vector to the AUSF.
5.2.3 Vector Generation in UDM/ARPF
This clause specifies the procedures for authentication vector request when the subscriber's authentication subscription
data is stored at the 5GS-UDR. In this case, the HSS requests the generation of the Authentication Vector for EPS
and/or IMS to the UDM.
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3GPP TS 23.632 version 17.3.0 Release 17 13 ETSI TS 123 632 V17.3.0 (2022-10)
NOTE: The UDM acts as AuC rather than as ARPF and it is required to generate authentication vectors as
defined in 3GPP TS 33.401 [8], 3GPP TS 33.402 [9], 3GPP TS 33.203 [10] and 3GPP TS 33.220 [11].
When the HSS receives an authentication vector request from a serving node (e.g. MME, SGSN, VLR, S-CSCF, BSF)
it shall check (by means of an EPC-UDR query) whether authentication vector generation for the identified subscriber
shall be done in the UDM. If so, the HSS shall make use of the Nudm_UEAuthentication GetHssAv service operation
to retrieve authentication vectors from the UDM.
Figure 4.2.3-1 shows the scenario where an authentication vector request for a subscriber is received by the HSS and
subscription data stored in the EPS-UDR indicate that for the subscriber authentication vector generation is to be
performed in the UDM.
Serving Node EPS-UDR Ud HSS UDM 5GS-UDR
1. Authentication Vector Request
2. Read
3. Nudm_UEAuthentication_GetHssAv Req
4. Nudr_DM_Query
5. Generate AV in ARPF
6. Nudm_UEAuthentication_GetHssAv Resp
7. Update
8. Authentication Vector Response

Figure 5.2.3-1: Authentication for a subscriber with authentication vector generation in UDM
1. The HSS receives an Authentication Vector request, containing the identity of the user (IMSI, or Public User
Identity and/or Private User Identity).
2. The HSS queries the EPS-UDR using the identity of the user to retrieve Authentication Subscription
Information. In this scenario the Authentication Subscription Information contains an indicator indicating that
authentication vector generation shall be performed in the UDM.
3. The HSS uses the Nudm_UEAuthentication_GetHssAv service operation to retrieve an authentication vector
from the UDM. The request contains the identity of the user, the type of the requested vector (E-
UTRAN/UTRAN or GERAN/ IMS-AKA and when available the visited PLMN-ID.
4. The UDM reads authentication subscription data from the 5GS-UDR.
5. The UDM (ARPF) calculates the requested authentication vectors taking into account the information received
in step 3 and the authentication subscription information retrieved from the 5GS-UDR.
6. The calculated authentication vectors are sent to the HSS.
7. The UDM updates the 5GS-UDR with the new sequence number.
8. The HSS forwards the authentication vectors to the serving node.
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3GPP TS 23.632 version 17.3.0 Release 17 14 ETSI TS 123 632 V17.3.0 (2022-10)
5.2.4 HSS using the Nudr SBI
When the HSS receives an S6a-AIR from the MME, it may check (by means of an EPC-UDR query) whether the
subscriber has an 5G subscription. If so, the HSS can use of the Nudr_DM_Query Get service operation to retrieve the
authentication subscription data from the 5GS UDR and generate the authentication vector.
Figure 5.2.4-1 shows the scenario where the authentication vector request for a 5G subscriber who also has an EPS
subscription is received by the UDM.
HSS 5GS-UDR
MME EPC-UDR
1. S6a-AIR
2. Ud Read
3. Nudr_DM_Query
4. Generate AV in AuC
5. S6a-AIA
6. Nudr_DM_Update
Figure 5.2.4-1: Authentication for 5G subscriber with EPS subscription
1. The HSS receives an Authentication Vector request containing the identity of the user (IMSI).
2. The HSS queries the EPC-UDR using the IMSI to retrieve Authentication Subscription Information. Since the
subscriber is a 5G subscriber the response indicates that the subscriber's authentication information is stored in
the 5GS UDR.
NOTE: Local configuration in the HSS may indicate that authentication subscription data for all subscribers can
be obtained from the 5G UDR and thus this step may be omitted.
3. The HSS uses the Nudr_DM_Query Get service operation to retrieve the authentication subscription data from
the 5GS UDR. The request contains the IMSI formatted as a SUPI.
4. The HSS (AuC) calculates the requested authentication vector taking into account the serving network name and
authentication method received in step 1 and the authentication subscription information retrieved from the 5GS-
UDR in step 3.
5. The calculated authentication vector is returned to the MME.
6. The HSS updates the 5GS-UDR with the new sequence number.
5.3 5GC-EPC Mobility Scenarios
5.3.1 General
As defined in 3GPP TS 23.501 [2], when interworking procedures with N26 are used, the UE operates in single-
registration mode. For the 3GPP access, either the AMF or the MME is registered in the HSS+UDM. This implies that:
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3GPP TS 23.632 version 17.3.0 Release 17 15 ETSI TS 123 632 V17.3.0 (2022-10)
- The registration of an MME in HSS for a UE that is capable to access the 5GC, triggers the cancellation of the
A
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