ETSI TS 129 531 V19.6.0 (2026-03)

5G; 5G System; Network Slice Selection Services; Stage 3 (3GPP TS 29.531 version 19.6.0 Release 19)

RTS/TSGC-0429531vj60

General Information

• Status: Not Published
• Technical Committee: 3GPP CT 4 - MAP/CAMEL/GTP/BCH/SS/TrFO/IMS/GUP/WLAN (formely CN4)
• Current Stage: 8 - Draft receipt by ETSI Secretariat
• Completion Date: 10-Mar-2026

Standards Content (Sample)

TECHNICAL SPECIFICATION
5G;
5G System;
Network Slice Selection Services;
Stage 3
(3GPP TS 29.531 version 19.6.0 Release 19)


3GPP TS 29.531 version 19.6.0 Release 19 1 ETSI TS 129 531 V19.6.0 (2026-03)

Reference
RTS/TSGC-0429531vj60
Keywords
5G
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ETSI
3GPP TS 29.531 version 19.6.0 Release 19 2 ETSI TS 129 531 V19.6.0 (2026-03)
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Legal Notice
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The cross reference between 3GPP and ETSI identities can be found at 3GPP to ETSI numbering cross-referencing.
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 29.531 version 19.6.0 Release 19 3 ETSI TS 129 531 V19.6.0 (2026-03)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 8
2 References . 8
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 9
4 Overview . 9
4.1 Introduction . 9
5 Services offered by the NSSF . 10
5.1 Introduction . 10
5.2 Nnssf_NSSelection Service . 10
5.2.1 Service Description . 10
5.2.2 Service Operations . 11
5.2.2.1 Introduction . 11
5.2.2.2 GET . 11
5.2.2.2.1 General . 11
5.2.2.2.2 Get service operation of Nnssf_NSSelection service . 12
5.2.2.2.3 Get service operation of Nnssf_NSSelection service during the PDU session establishment . 13
5.2.2.2.4 Get service operation of Nnssf_NSSelection service during UE configuration update
procedure . 14
5.2.2.2.5 Get service operation of Nnssf_NSSelection service during the PDN Connection
Establishment . 16
5.2.2.2.6 Get service operation of Nnssf_NSSelection service to retrieve the network slice information . 16
5.3 Nnssf_NSSAIAvailability Service . 17
5.3.1 Service Description . 17
5.3.2 Service Operations . 18
5.3.2.1 Introduction . 18
5.3.2.2 Update Service Operation . 18
5.3.2.2.1 General . 18
5.3.2.3 Subscribe Service Operation . 19
5.3.2.3.1 Creation of a subscription . 19
5.3.2.3.2 Modification of a subscription . 20
5.3.2.4 Unsubscribe Service Operation . 21
5.3.2.4.1 General . 21
5.3.2.5 Notify Service Operation . 21
5.3.2.5.1 General . 21
5.3.2.6 Delete Service Operation . 23
5.3.2.6.1 General . 23
5.3.2.7 Options Service Operation . 23
5.3.2.7.1 General . 23
6 API Definitions . 24
6.1 Nnssf_NSSelection Service API . 24
6.1.1 API URI . 24
6.1.2 Usage of HTTP . 24
6.1.2.1 General . 24
6.1.2.2 HTTP standard headers . 25
6.1.2.2.1 General . 25
6.1.2.2.2 Content type . 25
6.1.2.3 HTTP custom headers . 25
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6.1.2.3.1 General . 25
6.1.3 Resources . 25
6.1.3.1 Overview . 25
6.1.3.2 Resource: Network Slice Information . 26
6.1.3.2.1 Description . 26
6.1.3.2.2 Resource Definition . 26
6.1.3.2.3 Resource Standard Methods . 26
6.1.3.2.4 Resource Custom Operations . 28
6.1.4 Custom Operations without associated resources . 29
6.1.5 Notifications . 29
6.1.6 Data Model . 29
6.1.6.1 General . 29
6.1.6.2 Structured data types . 30
6.1.6.2.1 Introduction . 30
6.1.6.2.2 Type: AuthorizedNetworkSliceInfo . 31
6.1.6.2.3 Type: SubscribedSnssai . 35
6.1.6.2.4 Void . 36
6.1.6.2.5 Type: AllowedSnssai . 36
6.1.6.2.6 Type: AllowedNssai . 36
6.1.6.2.7 Type: NsiInformation . 37
6.1.6.2.8 Type: MappingOfSnssai . 37
6.1.6.2.9 Void . 38
6.1.6.2.10 Type: SliceInfoForRegistration . 38
6.1.6.2.11 Type: SliceInfoForPDUSession . 41
6.1.6.2.12 Type: ConfiguredSnssai . 41
6.1.6.2.13 Type: SliceInfoForUEConfigurationUpdate. 42
6.1.6.2.14 Type: NsagInfo . 44
6.1.6.2.15 Type: SnssaiInfo . 44
6.1.6.3 Simple data types and enumerations . 44
6.1.6.3.1 Introduction . 44
6.1.6.3.2 Simple data types . 44
6.1.6.3.3 Enumeration: RoamingIndication . 45
6.1.6.4 Binary data . 45
6.1.7 Error Handling . 45
6.1.7.1 General . 45
6.1.7.2 Protocol Errors . 45
6.1.7.3 Application Errors . 45
6.1.8 Feature negotiation . 45
6.1.9 Security . 46
6.1.10 HTTP redirection . 46
6.2 Nnssf_NSSAIAvailability Service API . 47
6.2.1 API URI . 47
6.2.2 Usage of HTTP . 47
6.2.2.1 General . 47
6.2.2.2 HTTP standard headers . 47
6.2.2.2.1 General . 47
6.2.2.2.2 Content type . 47
6.2.2.2.3 Accept-Encoding . 47
6.2.2.3 HTTP custom headers . 48
6.2.2.3.1 General . 48
6.2.3 Resources . 48
6.2.3.1 Overview . 48
6.2.3.2 Resource: NSSAI Availability Document . 49
6.2.3.2.1 Description . 49
6.2.3.2.2 Resource Definition . 49
6.2.3.2.3 Resource Standard Methods . 49
6.2.3.3 Resource: NSSAI Availability Notification Subscriptions Collection . 53
6.2.3.3.1 Description . 53
6.2.3.3.2 Resource Definition . 53
6.2.3.3.3 Resource Standard Methods . 53
6.2.3.4 Resource: Individual NSSAI Availability Notification Subscriptions . 55
6.2.3.4.1 Description . 55
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6.2.3.4.2 Resource Definition . 55
6.2.3.4.3 Resource Standard Methods . 55
6.2.3.5 Resource: NSSAI Availability Store . 57
6.2.3.5.1 Description . 57
6.2.3.5.2 Resource Definition . 57
6.2.3.5.3 Resource Standard Methods . 57
6.2.4 Custom Operations without associated resources . 58
6.2.5 Notifications . 59
6.2.5.1 General . 59
6.2.5.2 NSSAI Availability Notification . 59
6.2.5.2.1 Description . 59
6.2.5.2.2 Notification Definition . 59
6.2.5.2.3 Notification Standard Methods . 59
6.2.6 Data Model . 60
6.2.6.1 General . 60
6.2.6.2 Structured data types . 61
6.2.6.2.1 Introduction . 61
6.2.6.2.2 Type: NssaiAvailabilityInfo . 62
6.2.6.2.3 Type: SupportedNssaiAvailabilityData . 62
6.2.6.2.4 Type: AuthorizedNssaiAvailabilityData. 63
6.2.6.2.5 Type: RestrictedSnssai . 64
6.2.6.2.6 Type: AuthorizedNssaiAvailabilityInfo . 64
6.2.6.2.7 Type: PatchDocument . 64
6.2.6.2.8 Type: NssfEventSubscriptionCreateData . 65
6.2.6.2.9 Type: NssfEventSubscriptionCreatedData . 67
6.2.6.2.10 Type: NssfEventNotification . 68
6.2.6.2.11 Type: SnssaiReplacementSubscribeInfo . 70
6.2.6.2.12 Type: NsiUnavailabilitySubscribeInfo . 70
6.2.6.3 Simple data types and enumerations . 70
6.2.6.3.1 Introduction . 70
6.2.6.3.2 Simple data types . 71
6.2.6.3.3 Enumeration: NssfEventType . 71
6.2.6.4 Binary data . 71
6.2.7 Error Handling . 71
6.2.7.1 General . 71
6.2.7.2 Protocol Errors . 71
6.2.7.3 Application Errors . 71
6.2.8 Feature negotiation . 72
6.2.9 Security . 73
6.2.10 HTTP redirection . 74
Annex A (normative): OpenAPI specification . 75
A.1 General . 75
A.2 Nnssf_NSSelection API . 75
A.3 Nnssf_NSSAIAvailability API . 81
Annex B (informative): Change history . 93
History . 97

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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.
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 specifies the stage 3 protocol and data model for the Nnssf Service Based Interface. It provides
stage 3 protocol definitions and message flows, and specifies the API for each service offered by the NSSF.
The 5G System stage 2 architecture and procedures are specified in 3GPP TS 23.501 [2] and 3GPP TS 23.502 [3].
The Technical Realization of the Service Based Architecture and the Principles and Guidelines for Services Definition
are specified in 3GPP TS 29.500 [4] and 3GPP TS 29.501 [5].
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 23.502: "Procedures for the 5G System; Stage 2".
[4] 3GPP TS 29.500: "5G System; Technical Realization of Service Based Architecture; Stage 3".
[5] 3GPP TS 29.501: "5G System; Principles and Guidelines for Services Definition; Stage 3".
[6] OpenAPI: "OpenAPI Specification Version 3.0.0", https://spec.openapis.org/oas/v3.0.0.
[7] 3GPP TS 29.571: "5G System; Common Data Types for Service Based Interfaces; Stage 3".
[8] IETF RFC 6902: "JavaScript Object Notation (JSON) Patch".
[9] 3GPP TS 23.003: "Numbering, addressing and identification".
[10] IETF RFC 9113: "HTTP/2".
[11] 3GPP TS 33.501: "Security architecture and procedures for 5G system".
[12] IETF RFC 6749: "The OAuth 2.0 Authorization Framework".
[13] 3GPP TS 29.510: "Network Function Repository Services; Stage 3".
[14] IETF RFC 8259: "The JavaScript Object Notation (JSON) Data Interchange Format".
[15] IETF RFC 9457: "Problem Details for HTTP APIs".
[16] IETF RFC 1952: "GZIP file format specification version 4.3".
[17] 3GPP TR 21.900: "Technical Specification Group working methods".
[18] IETF RFC 9110: "HTTP Semantics".
[19] Void
[20] 3GPP TS 24.501: "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[21] 3GPP TS 38.413: "NG-RAN; NG Application Protocol (NGAP); Stage 3".
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[22] 3GPP TS 23.288: "Architecture enhancements for 5G System (5GS) to support network data
analytics services".
[23] 3GPP TS 29.503: "5G System; Unified Data Management Services; Stage 3".
3 Definitions and abbreviations
3.1 Definitions
For the purposes of the present document, the terms and definitions 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 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].
NSAG Network Slice AS Group
4 Overview
4.1 Introduction
Within the 5GC, the NSSF offers services to the AMF, SMF, NWDAF and NSSF in a different PLMN via the Nnssf
service based interface (see 3GPP TS 23.501 [2] and 3GPP TS 23.502 [3]).
Figure 4.1-1 provides the reference model (in service based interface representation and in reference point
representation), with focus on the NSSF and the scope of the present specification.
AMF
N22
NSSF N31 Nnssf NSSF
N34
NWDAF
SMF
Figure 4.1-1: NSSF in 5G System architecture
The functionalities supported by the NSSF are listed in clause 6.2.14 of 3GPP TS 23.501 [2].
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5 Services offered by the NSSF
5.1 Introduction
The NSSF supports the following services.
Table 5.1-1: NF Services provided by NSSF
Service Name Description Example
Consumer
Nnssf_NSSelection This service enables Network Slice selection in both AMF, V-NSSF,
the Serving PLMN and the HPLMN. SMF, NWDAF

This service also enables Network Slice selection in the
hosting operator's network for Indirect Network Sharing
deployments.
Nnssf_NSSAIAvailability This service enables to update the S-NSSAI(s) the NF AMF, V-NSSF
service consumer (e.g AMF) supports on a per TA
basis on the NSSF and to subscribe and notify any
change in status, on a per TA basis, of the SNSSAIs
available per TA (unrestricted) and the restricted S-
NSSAI(s) per PLMN in that TA in the serving PLMN of
the UE.
This service also enables the notification of the
Network Slice Replacement and Network Slice
Instance Replacement to the NF Service Consumer.
This service also enables to subscribe and unsubscribe
to the notification of any changes in the status of the
NSSAI validity time information.

Table 5.1-2 summarizes the corresponding APIs defined for this specification.
Table 5.1-2: API Descriptions
Service Name Clause Description OpenAPI Specification File apiName Annex
Nnssf_NSSelection 6.1 NSSF TS29531_Nnssf_NSSelection.yaml nnssf- A.2
Network Slice nsselection
Selection
Service
Nnssf_NSSAIAvaila6.2 NSSF NSSAI TS29531_Nnssf_NSSAIAvailability.y nnssf- A.3
bility Availability aml nssaiavaila
Service bility
5.2 Nnssf_NSSelection Service
5.2.1 Service Description
The Nnssf_NSSelection service is used by an NF Service Consumer (e.g. AMF, SMF, NWDAF or NSSF in a different
PLMN) to retrieve the information related to network slice in the non-roaming and roaming case.
It also enables the NSSF to provide to the AMF the Allowed NSSAI and the Configured NSSAI for the Serving PLMN.
It also enables the NSSF to provide to the AMF the NSAG information associated with the Configured NSSAI for the
Serving PLMN.
It also enables the NSSF to provide to the SMF+PGW-C the mapping of S-NSSAI(s) of the VPLMN to corresponding
HPLMN S-NSSAI(s).
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It also enables the NSSF to provide to the NWDAF the NSI ID(s) associated with the requested S-NSSAI.
It also enables the NSSF to provide to the AMF the slice mapping information in the case of Indirect Network Sharing.
The NF service consumer may discover the NSSF in the same PLMN based on the local configuration, or by using the
NRF-based discovery procedure as specified in clause 6.3.28 of 3GPP TS 23.501[2]. The addresses of the home NSSF
may be either locally configured in the visited NSSF or discovered based on the self-constructed FQDN as specified in
3GPP TS 23.003 [9].
5.2.2 Service Operations
5.2.2.1 Introduction
For the Nnssf_NSSelection service the following service operations are defined:
- Get.
5.2.2.2 GET
5.2.2.2.1 General
The Get operation shall be invoked by the AMF in the non-roaming or roaming scenario to retrieve:
- The slice selection information including the Allowed NSSAI, Configured NSSAI, target AMF Set or the list of
candidate AMF(s), and optionally
- The Mapping Of Allowed NSSAI;
- The Mapping Of Configured NSSAI;
- NSI ID(s) associated with the Network Slice instances of the Allowed NSSAI;
- NRF(s) to be used to select NFs/services within the selected Network Slice instance(s) and NRF to be used to
determine the list of candidate AMF(s) from the AMF Set, during Registration procedure;
- Information on whether the S-NSSAI(s) not included in the Allowed NSSAI which were part of the
Requested NSSAI are rejected in the serving PLMN or in the current TA;
- The Target NSSAI that includes the S-NSSAI(s) as defined in clause 5.3.4.3.3 of 3GPP TS 23.501 [2], and
- The NSAG information associated with Configured NSSAI as defined in clause 5.15.14 of
3GPP TS 23.501 [2].
- The NRF to be used to select NFs/services within the selected network slice instance, and optionally the NSI ID
associated with the S-NSSAI provided in the input, during the PDU Session Establishment procedure.
- The slice mapping information including the mapping of S-NSSAI(s) of the VPLMN to corresponding HPLMN
S-NSSAI(s), which is also applicable to Indirect Network Sharing case.
The Get operation shall also be invoked by the vNSSF in the roaming scenario to retrieve:
- The hNRF to be used to select NFs/services within the selected network slice instance in the HPLMN, and
optionally the NSI ID associated with the S-NSSAI provided in the input, during the PDU Session Establishment
procedure, which is also applicable to Indirect Network Sharing case.
The Get operation shall also be invoked by the SMF+PGW-C in VPLMN in the roaming scenario to retrieve:
- The slice mapping information including the mapping of S-NSSAI(s) of the VPLMN to corresponding HPLMN
S-NSSAI(s), during the PDN Connection Establishment procedure in EPC.
The Get operation shall also be invoked by the NWDAF to retrieve:
- The NSI ID associated with the S-NSSAI provided in the input.
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It is used in the following procedures:
- Registration procedure (see clause 4.2.2.2.2 of 3GPP TS 23.502 [3]);
- Registration with AMF re-allocation (see clause 4.2.2.2.3 of 3GPP TS 23.502 [3]);
- EPS to 5GS handover using N26 interface (see clause 4.11.1.2.2 of 3GPP TS
...