ETSI TS 138 401 V17.10.0 (2024-09)

5G; NG-RAN; Architecture description (3GPP TS 38.401 version 17.10.0 Release 17)

RTS/TSGR-0338401vha0

General Information

• Status: Not Published
• Technical Committee: 3GPP RAN 3 - lub specification, lur specification, lu specification and UTRAN & O&M
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 26-Sep-2024

Standards Content (Sample)

TECHNICAL SPECIFICATION
5G;
NG-RAN;
Architecture description
(3GPP TS 38.401 version 17.10.0 Release 17)

3GPP TS 38.401 version 17.10.0 Release 17 1 ETSI TS 138 401 V17.10.0 (2024-09)

Reference
RTS/TSGR-0338401vha0
Keywords
5G
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ETSI
3GPP TS 38.401 version 17.10.0 Release 17 2 ETSI TS 138 401 V17.10.0 (2024-09)
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ETSI
3GPP TS 38.401 version 17.10.0 Release 17 3 ETSI TS 138 401 V17.10.0 (2024-09)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 7
1 Scope . 8
2 References . 8
3 Definitions and abbreviations . 9
3.1 Definitions . 9
3.2 Abbreviations . 11
4 General principles . 12
5 General architecture . 12
5.1 General . 12
5.2 User plane . 13
5.3 Control plane . 13
6 NG-RAN architecture. 14
6.1 Overview . 14
6.1.1 Overall Architecture of NG-RAN . 14
6.1.2 Overall architecture for separation of gNB-CU-CP and gNB-CU-UP . 15
6.1.3 Overall Architecture of IAB . 16
6.1.4 Protocol stacks of IAB . 17
6.1.5 Overall Architecture of NR MBS . 19
6.1.6 Protocol stacks of L2 UE-to-Network Relay . 19
6.2 NG-RAN identifiers . 20
6.2.1 Principle of handling Application Protocol Identities . 20
6.2.2 gNB-DU ID . 22
6.2.3 ng-eNB-DU ID . 22
6.2.4 gNB-CU-UP ID . 23
6.2.5 RAN UE ID . 23
6.3 Transport addresses . 23
6.4 UE associations in NG-RAN Node . 23
6.5 MBS Session associations in NG-RAN Node . 24
7 NG-RAN functions description . . 25
7.0 General . 25
7.1 NG-RAN sharing . 26
7.2 Remote Interference Management . 26
7.3 Cross-Link Interference Management . 26
7.4 Support for Non-Public Networks . 26
7.5 RACH Optimisation Function . 26
7.6 Positioning . 26
7.7 Support for NR MBS . 26
7.7.1 Support of dynamic PTP and PTM switching. 26
7.8 PCI Optimisation Function . 27
7.9 Support for CCO . 27
7.9.1 General . 27
7.9.2 OAM requirements . 27
7.9.3 Dynamic coverage configuration changes . 27
7.10 Support of RAN visible QoE measurement. 27
8 Overall procedures in gNB-CU/gNB-DU Architecture . 27
8.1 UE Initial Access . 27
8.2 Intra-gNB-CU Mobility . 29
8.2.1 Intra-NR Mobility . 29
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8.2.1.1 Inter-gNB-DU Mobility . 29
8.2.1.2 Intra-gNB-DU handover . 30
8.2.1.3 Inter-gNB-DU Conditional Handover or Conditional PSCell Change . 31
8.2.2 EN-DC Mobility . 32
8.2.2.1 Inter-gNB-DU Mobility using MCG SRB . 32
8.2.2.2 Inter-gNB-DU Mobility using SCG SRB (SRB3) . 34
8.2.2.3 Inter-gNB-DU Conditional PSCell Change using MCG SRB without MN negotiation . 34
8.2.3 Intra-CU topology adaptation procedure . 36
8.2.3.1 Intra-CU topology adaptation procedure in SA. 36
8.2.3.2 Intra-CU topology adaptation procedure in NSA using MCG SRB. 39
8.2.3.3 Intra-CU topology adaptation procedure in NSA using SCG SRB (SRB3) . 41
8.2.4 Intra-CU topological redundancy procedure . 41
8.2.5 Intra-CU Backhaul RLF recovery for IAB-nodes in SA mode . 44
8.3 Mechanism of centralized retransmission of lost PDUs . 45
8.3.1 Centralized Retransmission in Intra gNB-CU Cases . 45
8.4 Multi-Connectivity operation . 46
8.4.1 Secondary Node Addition . 46
8.4.1.1 EN-DC . 46
8.4.2 Secondary Node Release (MN/SN initiated) . 47
8.4.2.1 EN-DC . 47
8.4.3 SCG suspend/resume in RRC_INACTIVE . 48
8.4.4 SCG Deactivation and Activation . 49
8.4.4.1 SN Addition with SCG Activation or Deactivation . 50
8.4.4.2 MN initiated SN Modification with SCG Activation or Deactivation . 51
8.4.4.3 SN initiated SN Modification with SCG Activation or Deactivation . 52
8.5 F1 Startup and cells activation . 52
8.6 RRC state transition. 54
8.6.1 RRC connected to RRC inactive. 54
8.6.2 RRC inactive to other states . 54
8.7 RRC connection reestablishment . 56
8.8 Multiple TNLAs for F1-C . 58
8.9 Overall procedures involving E1 and F1 . 59
8.9.1 UE Initial Access . 59
8.9.2 Bearer context setup over F1-U . 60
8.9.3 Bearer context release over F1-U . 61
8.9.3.1 gNB-CU-CP initiated bearer context release . 61
8.9.3.2 gNB-CU-UP initiated bearer context release . 62
8.9.4 Inter-gNB handover involving gNB-CU-UP change . 63
8.9.5 Change of gNB-CU-UP . 65
8.9.6 RRC State transition . 66
8.9.6.1 RRC Connected to RRC Inactive . 66
8.9.6.2 RRC Inactive to other states . 67
8.9.7 Trace activation/deactivation over F1 and E1 . 69
8.9.8 BH RLC channel establishment procedure . 69
8.9.9 Traffic Mapping . 71
8.9.9.1 Traffic Mapping from IP-layer to Layer-2 . 71
8.9.9.2 BH RLC Channel Mapping on BAP Layer . 71
8.9.10 IAB-node release . 71
8.9.10.1 IAB-node orderly release . 72
8.9.10.2 IAB-node disorderly release. 72
8.9.11 IAB-node OAM . 72
8.9.12 Handling of IAB-MTs in INACTIVE State . 72
8.9.13 IP Address Allocation for IAB-nodes . 72
8.9.14 (void) . 73
8.9.15 (void) . 73
8.9.16 (void) . 73
8.9.17 IAB-node authorization . 73
8.9.17.1 IAB-node in NSA . 73
8.9.17.2 IAB-node with single IAB-donor in SA. 74
8.9.17.2.1 IAB-node is single-connected . 74
8.9.17.2.2 IAB-node is NR dual-connected . 74
8.9.17.3 IAB-node is served by two IAB-donors in SA . 74
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8.10 Multiple TNLAs for E1 . 74
8.11 Support of Network Sharing with multiple cell-ID broadcast . 76
8.11.1 General . 76
8.11.2 Initial Registration – separate PLMN signalling . 76
8.11.3 RRC Connection Reestablishment – separate PLMN signalling . 77
8.11.4 Support of shared signalling transport . 78
8.12 IAB-node Integration Procedure . 78
8.12.1 Standalone IAB integration . 78
8.12.2 NSA IAB Integration procedure . 79
8.13 Overall procedures for MDT . 81
8.13.0 General . 81
8.13.1 Signalling based MDT activation . 81
8.13.2 Management based MDT activation . 81
8.13.2.1 General . 81
8.13.2.2 Management based MDT Activation in gNB-CU-CP . 82
8.13.2.3 Management based MDT Activation in gNB-DU . 82
8.13.2.4 Management based MDT Activation in gNB-CU-UP . 83
8.13.2.5 User consent propagation in EN-DC . 84
8.13.2.6 User consent propagation in MR-DC with 5GC . 85
8.13.2.7 Management based trace activation in MR-DC with 5GC . 86
8.13.3 Alignment of MDT and QoE Measurements . 87
8.13.4 MDT reporting . 87
8.14 Self-optimisation . 87
8.14.1 Overall procedures for MRO . 87
8.14.1.1 Signalling of RLF information from gNB-CU to gNB-DU . 88
8.14.1.2 Signalling of RACH information from gNB-CU to gNB-DU . 88
8.15 Overall procedures for NR MBS . 89
8.15.1 General . 89
8.15.1.1 Broadcast MBS Session Setup . 89
8.15.1.2 Multicast MBS Session Context Establishment . 90
8.15.1.3 Multicast MRB type re-configuration with F1-U ptp-retransmission tunnel establishment . 92
8.15.2 Mobility procedure for Multicast . 93
8.15.2.1 Inter-gNB-CU Mobility between MBS Supporting nodes . 93
8.16 Overall procedures for CPAC . 94
8.16.1 MN initiated Conditional PSCell Addition . 94
8.16.2 MN initiated conditional SN Change . 95
8.16.3 SN initiated conditional inter-SN Change . 95
8.17 IAB Inter-CU Topology Management . 95
8.17.1 IAB Inter-donor-DU Re-routing . 95
8.17.2 IAB Inter-CU Topology Redundancy . 96
8.17.2.1 IAB Inter-CU topological redundancy procedure . 96
8.17.3 IAB Inter-CU Topology Adaptation . 98
8.17.3.1 IAB inter-CU topology adaptation procedure . 98
8.17.3.2 IAB inter-CU topology adaptation procedure with descendant IAB-node. 101
8.17.4 IAB Inter-CU Backhaul RLF recovery for single connected IAB-node . 103
8.18 Overall procedure for Small Data Transmission during RRC Inactive . 106
8.18.1 RACH based SDT . 106
8.18.2 CG based SDT . 107
8.18.3 RA-SDT or non-SDT with CG-SDT configuration . 108
8.19 Overall procedures for L2 UE-to-Network Relay . 109
8.19.1 Remote UE initial access . 109
8.19.2 Remote UE RRC Reestablishment . 112
8.19.3 Remote UE RRC Inactive to other states . 114
8.19.4 Service Continuity for L2 U2N relay . 116
8.19.4.1 Inter-gNB-DU switch from direct to indirect path . 116
8.19.4.2 Intra-gNB-DU switch from direct to indirect path . 118
8.20 Void . 119
9 Synchronization . 119
9.1 gNB Synchronization . 119
10 NG-RAN interfaces . 120
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10.1 NG interface . 120
10.2 Xn interface . 120
10.3 F1 interface . 120
10.4 E1 interface . 120
10.5 Antenna interface - general principles . 120
11 Overall procedures in NG-RAN Architecure . 121
11.1 Multiple TNLAs for Xn-C . 121
Annex A (informative): Deployment scenarios of gNB/en-gNB . 122
Annex B: NG-RAN Architecture for Radio Access Network Sharing with
multiple cell ID broadcast (informative) . 123
Annex C (informative): Change History . 124
History . 126

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3GPP TS 38.401 version 17.10.0 Release 17 7 ETSI TS 138 401 V17.10.0 (2024-09)
Foreword
rd
This Technical Specification has been produced by the 3 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.
ETSI
3GPP TS 38.401 version 17.10.0 Release 17 8 ETSI TS 138 401 V17.10.0 (2024-09)
1 Scope
The present document describes the overall architecture of the NG-RAN, including interfaces NG, Xn and F1 interfaces
and their interaction with the radio interface.
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 38.300: "NR; Overall description; Stage-2".
[3] 3GPP TS 23.501: "System Architecture for the 5G System".
[4] 3GPP TS 38.473: "NG-RAN; F1 application protocol (F1AP)".
[5] 3GPP TS 38.414: "NG-RAN; NG data transport".
[6] 3GPP TS 38.424: "NG-RAN; Xn data transport".
[7] 3GPP TS 38.474: "NG-RAN; F1 data transport".
[8] ITU-T Recommendation G.823 (2000-03): "The control of jitter and wander within digital
networks which are based on the 2048 kbit/s hierarchy".
[9] ITU-T Recommendation G.824 (2000-03): "The control of jitter and wander within digital
networks which are based on the 1544 kbit/s hierarchy".
[10] ITU-T Recommendation G.825 (2001-08): "The control of jitter and wander within digital
networks which are based on the synchronous digital hierarchy (SDH)".
[11] ITU-T Recommendation G.8261/Y.1361 (2008-04): "Timing and Synchronization aspects in
Packet networks".
[12] 3GPP TS 37.340: "NR; Multi-connectivity; Overall description; Stage-2".
[13] 3GPP TS 33.501: "Security Architecture and Procedures for 5G System".
[14] 3GPP TS 38.410: "NG-RAN; NG general aspect and principles".
[15] 3GPP TS 38.420: "NG-RAN; Xn general aspects and principles"
[16] 3GPP TS 38.470: "NG-RAN; F1 general aspects and principles".
[17] 3GPP TS 38.460: "NG-RAN; E1 general aspects and principles".
[18] 3GPP TS 33.210: "3G security; Network Domain Security (NDS); IP Network Layer Security".
[19] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA), Evolved Universal
Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2".
[20] 3GPP TS 32.422: "Trace control and configuration management".
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3GPP TS 38.401 version 17.10.0 Release 17 9 ETSI TS 138 401 V17.10.0 (2024-09)
[21] 3GPP TS 37.470: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and NG-
RAN; W1 general aspects and principles; Stage-2".
[22] 3GPP TS 38.340: "NR; Backhaul Adaptation Protocol (BAP) specification".
[23] 3GPP TS 38.331: "NR; Radio Resource Control (RRC) protocol specification".
[24] 3GPP TS 38.425: "NG-RAN; NR user plane Protocol".
[25] 3GPP TS 38.305: "NG Radio Access Network (NG-RAN); Stage 2 functional specification of
User Equipment (UE) positioning in NG-RAN".
[26] 3GPP TS 38.472: "NG-RAN; F1 signalling transport".
[27] 3GPP TS 23.247: " Architectural enhancements for 5G multicast-broadcast services; Stage 2".
[28] 3GPP TS 36.401: "Evolved Universal Terrestrial Radio Access Network (E-UTRAN);
Architecture Description".
[29] IETF RFC 4555 (2006-06): "RFC IKEv2 Mobility and Multihoming Protocol (MOBIKE)".
[30] 3GPP TS 38.321 “NR; Medium Access Control (MAC) protocol specification”.
[31] 3GPP TS 37.320: "Radio measurement collection for Minimization of Drive Tests (MDT); Overall
description; Stage 2".
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].
Associated QoS Flow: as defined in TS 23.247 [27].
Associated QoS flow information: Information encompassing: QoS flow QoS parameters for associated QoS flows
and mapping information between mapped (unicast) QoS flows and associated QoS flows. The respective information
is included in a way that non-supporting RAN nodes would not establish respective RAN resources irrespective the
multicast session state.
Boundary IAB-node: an IAB-node with one RRC interface terminating at a different IAB-donor-CU than the F1
interface. This definition applies to partial migration, inter-donor redundancy and inter-donor RLF recovery.
Conditional Handover: as defined in TS 38.300 [2].
Conditional PSCell Addition: as defined in TS 37.340 [12].
Conditional PSCell Change: as defined in TS 37.340 [12].
DAPS Handover: as defined in TS 38.300 [2].
eNB-CP: as defined in TS 36.401 [28].
eNB-UP: as defined in TS 36.401 [28].
en-gNB: as defined in TS 37.340 [12].
Early Data Forwarding: as defined in TS 38.300 [2].
F1-terminating IAB-donor of boundary IAB-node: Refers to the IAB-donor that terminates F1 for the boundary
IAB-node.
gNB: as defined in TS 38.300 [2].
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3GPP TS 38.401 version 17.10.0 Release 17 10 ETSI TS 138 401 V17.10.0 (2024-09)
gNB Central Unit (gNB-CU): a logical node hosting RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP
protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface
connected with the gNB-DU.
gNB Distributed Unit (gNB-DU): a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and its
operation is partly controlled by gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only
one gNB-DU. The gNB-DU terminates the F1 interface connected with the gNB-CU. For DC operation, the MgNB-DU
designates the gNB-DU of an en-gNB or a gNB acting as master node, and the SgNB-DU designates the gNB-DU of an
en-gNB or a gNB acting as secondary node.
gNB-CU-Control Plane (gNB-CU-CP): a logical node hosting the RRC and the control plane part of the PDCP
protocol of the gNB-CU for an en-gNB or a gNB. The gNB-CU-CP terminates the E1 interface connected with the
gNB-CU-UP and the F1-C interface connected with the gNB-DU. For DC operation, the MgNB-CU-CP designates the
gNB-CU-CP of the gNB-CU for an en-gNB or a gNB acting as master node, and the SgNB-CU-CP designates the gNB-
CU-CP of the gNB-CU for an en-gNB or a gNB acting as secondary node.
gNB-CU-User Plane (gNB-CU-UP): a logical node hosting the user plane part of the PDCP protocol of the gNB-CU
for an en-gNB, and the user plane part of the PDCP protocol and the SDAP protocol of the gNB-CU for a gNB. The
gNB-CU-UP terminates the E1 interface connected with the gNB-CU-CP and the F1-U interface connected with the
gNB-DU. For DC operation, the MgNB-CU-UP designates the gNB-CU-UP of the gNB-CU for an en-gNB or a gNB
acting as master node, and the the SgNB-CU-UP designates the gNB-CU-UP of the gNB-CU for an en-gNB or a gNB
acting as secondary node.
IAB-node: as defined in TS 38.300 [2].
IAB-donor: as defined in TS 38.300 [2].
IAB-donor-CU: the gNB-CU of an IAB-donor, terminating the F1 interface towards IAB-nodes and IAB-donor-DU.
IAB-donor-DU: the gNB-DU of an IAB-donor, hosting the IAB BAP sublayer (as defined in TS 38.340 [22]),
providing wireless backhaul to IAB-nodes.
IAB-DU: as defined in TS 38.300 [2].
IAB-MT: as defined in TS 38.300 [2].
IAB Topology: as defined in TS 38.300 [2].
Mapped QoS flows: Unicast QoS flows requested to be established, i.e. included in the legacy QoS flow lists in a way,
that non-support RAN nodes would attempt to establish unicast QoS flows and supporting RAN nodes can identify
them as mapped QoS flows based on the associated QoS information.
Master node: as defined in TS 37.340 [12].
Master gNB: see TS 37.340 [12].
MBS session resource: This term is used for specification of NG, Xn, F1 and E1 interfaces. It denotes NG-RAN
interface and radio resources provided to support an MBS Session.
ng-eNB: as defined in TS 38.300 [2].
ng-eNB Central Unit (ng-eNB-CU): as defined in TS 37.470 [21].
ng-eNB Distributed Unit (ng-eNB-DU): as defined in TS 37.470 [21].
ng-eNB-CU-Control Plane (ng-eNB-CU-CP): a logical node hosting the RRC and the control plane part of the PDCP
protocol of the ng-eNB-CU for an ng-eNB. The ng-eNB-CU-CP terminates the E1 interface connected with the ng-
eNB-CU-UP and the W1-C interface connected with the ng-eNB-DU.
ng-eNB-CU-User Plane (ng-eNB-CU-UP): a logical node hosting the user plane part of the PDCP protocol and the
SDAP
...