ETSI TS 124 502 V15.5.0 (2019-10)

TECHNICAL SPECIFICATION
5G;
Access to the 3GPP 5G Core Network (5GCN) via non-3GPP
access networks
(3GPP TS 24.502 version 15.5.0 Release 15)

3GPP TS 24.502 version 15.5.0 Release 15 1 ETSI TS 124 502 V15.5.0 (2019-10)

Reference
RTS/TSGC-0124502vf50
Keywords
5G
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3GPP TS 24.502 version 15.5.0 Release 15 2 ETSI TS 124 502 V15.5.0 (2019-10)
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Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 7
1 Scope . 8
2 References . 8
3 Definitions, symbols and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 10
4 General . 10
4.1 Overview . 10
4.2 Untrusted access . 10
4.3 Identities . 11
4.3.1 User identities . 11
4.3.2 FQDN for N3IWF Selection . 11
4.4 Quality of service support . 11
4.4.1 General . 11
4.4.2 QoS differentiation in untrusted non-3GPP access . 11
4.4.2.1 General . 11
4.4.2.2 QoS signalling . 11
4.4.2.3 QoS differentiation in user plane . 12
4.4.2.4 Reflective QoS . 12
4.4.2.5 QoS enforcement . 12
5 Network discovery and selection . 12
5.1 General . 12
5.2 Access network discovery procedure . 12
5.2.1 General . 12
5.2.2 Discovering availability of WLAN access networks . 12
5.3 Access network selection procedure. 13
5.3.1 General . 13
5.3.2 WLAN selection procedure . 13
5.3.2.1 General . 13
5.3.2.2 Manual mode WLAN selection. 13
5.3.2.3 Automatic mode WLAN selection . 13
5.4 Access network reselection procedure . 14
5.4.1 General . 14
5.4.2 WLAN reselection procedure . 14
6 UE - 5GC network protocols . 15
6.1 General . 15
6.2 Untrusted Accesses. 15
6.3 Authentication and authorization for accessing 5GS via an untrusted non-3GPP access network . 15
6.3.1 General . 15
6.4 Handling of ANDSP Information . 15
6.4.1 General . 15
6.4.2 UE procedures . 16
6.4.2.1 General . 16
6.4.2.2 Use of WLAN selection information . 16
6.4.2.3 Use of N3AN node configuration information . 16
6.4.3 ANDSP information from the network . 16
7 Security association management procedures . 16
7.1 General . 16
7.2 N3AN node selection procedure . 17
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7.2.1 General . 17
7.2.2 N3AN node configuration information . 17
7.2.3 Determination of the country the UE is located in . 17
7.2.4 N3AN node selection . 17
7.2.4.1 General . 17
7.2.4.2 Determine if the visited country mandates the selection of N3IWF in this country. 18
7.2.4.3 UE procedure when the UE only supports connectivity with N3IWF . 18
7.2.4.4 UE procedure when the UE supports connectivity with N3IWF and ePDG . 20
7.2.4.4.1 General . 20
7.2.4.4.2 N3AN node selection for IMS service . 20
7.2.4.4.3 N3AN node selection for Non-IMS service . 23
7.3 IKE SA establishment procedure . 26
7.3.1 General . 26
7.3.2 IKE SA and signalling IPsec SA establishment procedure . 26
7.3.2.1 IKE SA and signalling IPsec SA establishment initiation . 26
7.3.2.2 IKE SA and signalling IPsec SA establishment accepted by the network . 26
7.3.2.3 IKE SA and signalling IPsec SA establishment not accepted by the network . 28
7.3.3 EAP-5G session over non-3GPP access . 29
7.3.3.1 General . 29
7.3.3.2 EAP-5G session completion initiated by the network . 30
7.3.3.3 EAP-5G session completion initiated by the UE . 30
7.3.4 Abnormal cases in the UE . 31
7.3.5 Abnormal cases in the N3IWF . 31
7.4 IKEv2 SA deletion procedure . 31
7.4.1 General . 31
7.4.2 IKE SA deletion procedure initiated by the N3IWF . 32
7.4.2.1 IKE SA deletion initiation . 32
7.4.2.2 IKE SA deletion accepted by the UE . 32
7.4.2.3 Abnormal cases in the N3IWF . 32
7.4.3 IKE SA deletion procedure initiated by the UE . 32
7.4.3.1 IKE SA deletion initiation . 32
7.4.3.2 IKE SA deletion accepted by the N3IWF . 32
7.4.3.3 Abnormal cases in the UE . 33
7.5 User plane IPsec SA creation procedure . 33
7.5.1 General . 33
7.5.2 Child SA creation procedure initiation . 33
7.5.3 Child SA creation procedure accepted by the UE . 33
7.5.4 Child SA creation procedure not accepted by the UE . 33
7.5.5 Abnormal cases in the UE . 34
7.5.6 Abnormal cases in the N3IWF . 34
7.6 IPsec SA modification procedure . 34
7.6.1 General . 34
7.6.2 N3IWF procedure for IPsec child SA modification . 34
7.6.3 UE procedure for IPsec child SA modification. 34
7.7 IPSec SA deletion procedure . 35
7.7.1 General . 35
7.7.2 N3IWF-initated child SA deletion procedure . 35
7.7.2.1 N3IWF-initiated child SA deletion procedure initiation . 35
7.7.2.2 N3IWF-initiated child SA deletion procedure accepted by the UE . 35
7.7.2.3 Abnormal cases in the N3IWF . 35
7.7.3 UE-initiated child SA deletion procedure . 35
7.7.3.1 UE-initiated child SA deletion procedure initiation . 35
7.7.3.2 UE-initiated child SA deletion procedure accepted by the N3IWF . 36
7.7.3.3 Abnormal cases in the UE . 36
7.7.4 Abnormal cases in the UE . 36
7.7.5 Abnormal cases in the N3IWF . 36
7.8 UE-initiated liveness check procedure . 36
7.8.1 General . 36
7.8.2 UE-initiated liveness check procedure initiation . 36
7.8.3 UE-initiated liveness check procedure completion . 36
7.8.4 Abnormal cases . 37
7.9 Network-initiated liveness check procedure . 37
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7.9.1 General . 37
7.9.2 Network-initiated liveness check procedure initiation . 37
7.9.3 Network-initiated liveness check procedure completion . 37
7.9.4 Abnormal cases . 37
7.10 IKE SA rekeying procedure . 37
7.10.1 General . 37
7.10.2 N3IWF-initiated IKE SA rekeying procedure . 37
7.10.2.1 N3IWF-initiated IKE SA rekeying procedure initiation . 37
7.10.2.2 N3IWF-initiated IKE SA rekeying procedure completion . 38
7.10.2.3 Abnormal cases . 38
7.10.3 UE-initiated IKE SA rekeying procedure . 38
7.10.3.1 UE-initiated IKE SA rekeying procedure initiation . 38
7.10.3.2 UE-initiated IKE SA rekeying procedure completion . 38
7.10.3.3 Abnormal cases . 38
7.11 IPsec SA rekeying procedure . 38
7.11.1 General . 38
7.11.2 N3IWF-initiated IPsec SA rekeying procedure . 39
7.11.2.1 N3IWF-initiated IPsec SA rekeying procedure initiation . 39
7.11.2.2 N3IWF-initiated IPsec SA rekeying procedure completion . 39
7.11.2.3 Abnormal cases . 39
7.11.3 UE-initiated IPsec SA rekeying procedure . 39
7.11.3.1 UE-initiated IPsec SA rekeying procedure initiation . 39
7.11.3.2 UE-initiated IPsec SA rekeying procedure completion . 39
7.11.3.3 Abnormal cases . 39
8 Message transport procedures . 39
8.1 General . 39
8.2 Transport of NAS messages over control plane . 40
8.2.1 General . 40
8.2.2 TCP packet encapsulation . 40
8.2.3 Establishment of TCP connection for transport of NAS messages . 42
8.2.4 Transport of NAS messages over TCP connection . 42
8.2.5 Release of TCP connection for transport of NAS messages . 42
8.3 Transport of messages over user plane . 42
8.3.1 General . 42
8.3.2 Generic routing encapsulation (GRE) . 43
9 Parameters and coding. 44
9.1 General . 44
9.2 3GPP specific coding information . 44
9.2.1 GUAMI . 44
9.2.2 Establishment cause for non-3GPP access . 45
9.2.3 PLMN ID . 45
9.2.4 IKEv2 Notify Message Type value . 46
9.2.4.1 General . 46
9.2.4.2 Private Notify Message - Error Types . 46
9.2.4.3 Private Notify Message - Status Types . 47
9.3 IETF RFC coding information . 48
9.3.1 IKEv2 Notify payloads . 48
9.3.1.1 5G_QOS_INFO Notify payload. 48
9.3.1.2 NAS_IP4_ADDRESS Notify payload . 49
9.3.1.3 NAS_IP6_ADDRESS Notify payload . 50
9.3.1.4 UP_IP4_ADDRESS Notify payload . 50
9.3.1.5 UP_IP6_ADDRESS Notify payload . 51
9.3.1.6 NAS_TCP_PORT Notify payload . 51
9.3.1.7 N3GPP_BACKOFF_TIMER Notify payload . 52
9.3.2 EAP-5G method . 52
9.3.2.1 General . 52
9.3.2.2 Message format . 53
9.3.2.2.1 EAP-Request/5G-Start message . 53
9.3.2.2.2 EAP-Response/5G-NAS message . 53
9.3.2.2.3 EAP-Request/5G-NAS message . 56
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9.3.2.2.4 EAP-Request/5G-Stop message . 56
9.3.3 GRE encapsulated user data packet . 57
9.4 NAS message envelope . 59
Annex A (informative): Change history . 60
History . 63

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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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1 Scope
The present document specifies non-3GPP access network discovery and selection procedures, the access authorization
procedure used for accessing untrusted non-3GPP access networks.
The present document also specifies the security association management procedures used for establishing IKEv2 and
IPsec security associations between the UE and the N3IWF and the procedures for transporting messages between the
UE and the N3IWF over the non-3GPP access networks.
The present document is applicable to the UE and the network. In this technical specification the network refers to the
3GPP 5GCN and the untrusted non-3GPP access network.
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 24.501: "Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[5] 3GPP TS 33.501: "Security architecture and procedures for 5G System".
[6] IETF RFC 7296: "Internet Key Exchange Protocol Version 2 (IKEv2)".
[7] 3GPP TS 24.302: "Access to the 3GPP Evolved Packet Core (EPC) via non-3GPP access
networks; Stage 3".
[8] 3GPP TS 23.003: "Numbering, addressing and identification".
[9] IETF RFC 3748: "Extensible Authentication Protocol (EAP)".
[10] 3GPP TS 33.402: "3GPP System Architecture Evolution (SAE); Security aspects of non-3GPP
accesses."
[11] IETF RFC 4303: "IP Encapsulating Security Payload (ESP)".
[12] IETF RFC 4301: "Security Architecture for the Internet Protocol".
[13] 3GPP TS 23.122: "Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle
mode".
[14] IETF RFC 2784: "Generic Routing Encapsulation (GRE)".
[15] IETF RFC 2890: "Key and Sequence Number Extensions to GRE".
[16] 3GPP TS 23.503: "Policy and Charging Control Framework for the 5G System".
[17] 3GPP TS 24.526: "User Equipment (UE) policies for 5G System (5GS); Stage 3".
[18] 3GPP TS 23.402: "Architecture enhancements for non-3GPP accesses".
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[19] IEEE Std 802.11-2012: "IEEE Standard for Information technology - Telecommunications and
information exchange between systems - Local and metropolitan area networks - Specific
requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications".
[20] Wi-Fi Alliance: "Hotspot 2.0 (Release 2) Technical Specification, version 1.0.0", 2014-08-08.
[21] ITU-T Recommendation E.212: "The international identification plan for public networks and
subscriptions", 2016-09-23.
[22] 3GPP TS 24.007: "Mobile radio interface signalling layer 3; General aspects".
[23] IETF RFC 4555: "IKEv2 Mobility and Multihoming Protocol (MOBIKE)".
[24] IETF RFC 791: "INTERNET PROTOCOL".
[25] IETF RFC 8200: "Internet Protocol, Version 6 (IPv6) Specification".
[26] IETF RFC 2474: "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6
Headers".
[27] IETF RFC 793: "Transmission Control Protocol".
[28] 3GPP TS 24.008: "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3".
[29] 3GPP TS 38.413: "NG Application Protocol (NGAP)".
3 Definitions, symbols 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].
MTU: Maximum transmission unit (MTU) is the largest PDU size which can be transmitted and received by a network
entity in one single IP packet without any need for IP fragmentation.
NWu: In this specification, NWu is the reference point between the UE and the N3IWF for establishing secure
tunnel(s) between the UE and the N3IWF so that control-plane and user-plane exchanged between the UE and the 5G
core network is transferred securely over untrusted non-3GPP access.
For the purposes of the present document, the following terms and definitions given in 3GPP TS 23.501 [2] apply:
5G Access Network
5G Core Network
5G QoS flow
5G QoS identifier
5G System
PDU Session
For the purposes of the present document, the following terms and definitions given in 3GPP TS 23.003 [8] apply:
NAI
For the purposes of the present document, the following terms and definitions given in 3GPP TS 33.501 [5] apply:
SUPI
SUCI
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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].
5GCN 5G Core Network
5GS 5G System
5G-AN 5G Access Network
5QI 5G QoS Identifier
AMF Access and Mobility Management Function
ANDS Access Network Discovery and Selection
ANDSP Access Network Discovery and Selection Policy
AUSF Authentication Server Function
CP Control Plane
DL Downlink
DNS Domain Name System
DSCP Differentiated Services Code Point
ePDG Evolved Packet Data Gateway
ESP Encapsulating Security Payload
FQDN Fully Qualified Domain Name
H-PCF A PCF in the HPLMN
IP Internet Protocol
IPsec Internet Protocol Security
N3AN Non-3GPP Access Network
N3IWF Non-3GPP InterWorking Function
NAI Network Access Identifier
NAS Non Access Stratum
PCF Policy control Function
PDU Protocol Data Unit
QFI QoS Flow Identifier
RQI Reflective QoS Indicator
SA Security Association
SPI Security Parameters Index
SUPI Subscription Permanent Identifier
SUCI Subscription Concealed Identifier
TCP Transmission Control Protocol
UL Uplink
UP User Plane
UPF User Plane Function
V-PCF A PCF in the VPLMN
WLANSP WLAN Selection Policy
4 General
4.1 Overview
The 5G core network supports the connectivity of the UE via non-3GPP access networks. In this release of
specification, only untrusted non-3GPP access is supported.
4.2 Untrusted access
For an untrusted non-3GPP access network, the communication between the UE and the 5GCN is not trusted to be
secure.
For an untrusted non-3GPP access network, to secure communication between the UE and the 5GCN, a UE establishes
secure connection to the 5G core network over untrusted non-3GPP access via the N3IWF. The UE performs
registration to the 5G core network during the IKEv2 SA establishment procedure as specified in 3GPP TS 24.501 [4]
and IETF RFC 7296 [6]. After the registration, the UE supports NAS signalling with 5GCN using the N1 reference
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point as specified in 3GPP TS 24.501 [4]. The N3IWF interfaces the 5GCN CP function via the N2 interface to the
AMF and the 5GCN UP functions via N3 interface to the UPF as described in 3GPP TS 23.501 [2].
4.3 Identities
4.3.1 User identities
When the UE accesses the 5GCN over non-3GPP access networks, the same permanent identities for 3GPP access are
used to identify the subscriber for non-3GPP access authentication, authorization and accounting services.
The Subscription Permanent Identifier (SUPI) is defined in 3GPP TS 33.501 [5]. The SUPI can contain either an IMSI
or a network specific identifier as specified in 3GPP TS 23.501 [2]. A SUPI containing an IMSI is defined in
3GPP TS 23.003 [8]. A SUPI containing a network specific identifier always takes the form of a NAI as defined in
3GPP TS 23.003 [8].
The Subscription Concealed Identifier (SUCI) is a privacy preserving identifier containing the concealed SUPI as
specified in 3GPP TS 33.501 [5]. SUCI is calculated from SUPI. When the SUPI contains an IMSI, the corresponding
SUCI is derived as specified in 3GPP TS 23.003 [8]. When the SUPI contains a network specific identifier, the
corresponding SUCI in NAI format is derived as specified in 3GPP TS 23.003 [8].
User identification in non-3GPP accesses can require additional identities that are out of the scope of 3GPP.
4.3.2 FQDN for N3IWF Selection
An N3IWF FQDN is either provisioned by the home operator or constructed by the UE in either the Operator Identifier
FQDN format or the Tracking Area Identity FQDN format as specified in 3GPP TS 23.003 [8],
The N3IWF FQDN is used as input to the DNS mechanism for N3IWF selection.
4.4 Quality of service support
4.4.1 General
When the UE accesses the 3GPP 5G System (5GS) via non-3GPP access networks, the same QoS flow based 5G QoS
model and principles are followed as described in 3GPP TS 23.501 [2]. For PDU sessions that were established over
non-3GPP access, the QoS flow remains to be the finest granularity of QoS differentiation in the PDU Session.
4.4.2 QoS differentiation in untrusted non-3GPP access
4.4.2.1 General
For untrusted non-3GPP access, the N3IWF is the access network node that provides QoS signalling to support QoS
differentiation and mapping of QoS flows to non-3GPP access resources.
4.4.2.2 QoS signalling
A QoS flow is controlled by the SMF and can be preconfigured, or established via the UE requested PDU Session
establishment via untrusted non-3GPP access procedure, the UE or network requested PDU session modification via
untrusted non-3GPP access procedure. (see 3GPP TS 23.502 [3]),
During PDU session establishment, based on local policies, pre-configuration and the QoS profiles received, the
N3IWF determines the number of IPsec child SAs to establish and the QoS profiles associated with each IPsec child
SA. The N3IWF then initiates IPsec SA creation procedure to establish Child SAs associating to the QoS flows of the
PDU session.
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4.4.2.3 QoS differentiation in user plane
For uplink, the UE associates an uplink user data packet with a QFI as specified in 3GPP TS 24.501 [4]. The UE shall
then encapsulate the uplink user data packet and the QFI associated with the uplink user data packet in the GRE header
and select IPsec child SA based on PDU session and QFI associated with the
...