ETSI TS 138 470 V15.2.

0 (2018-07)

TECHNICAL SPECIFICATION

5G;
NG-RAN;
F1 general aspects and principles
(3GPP TS 38.470 version 15.2.0 Release 15)
 3GPP TS 38.470 version 15.2.0 Release 15 1 ETSI TS 138 470 V15.2.0 (2018-07)

Reference
DTS/TSGR-0338470vf20

Keywords
5G

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3GPP TS 38.470 version 15.2.0 Release 15 2 ETSI TS 138 470 V15.2.0 (2018-07)

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Foreword
This Technical Specification (TS) has been produced by ETSI 3rd Generation Partnership Project (3GPP).

The present document may refer to technical specifications or reports using their 3GPP identities, UMTS identities or
GSM identities. These should be interpreted as being references to the corresponding ETSI deliverables.

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Modal verbs terminology

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3GPP TS 38.470 version 15.2.0 Release 15 3 ETSI TS 138 470 V15.2.0 (2018-07)

Contents
Intellectual Property Rights ................................................................................................................................2
Foreword.............................................................................................................................................................2
Modal verbs terminology....................................................................................................................................2
Foreword.............................................................................................................................................................4
1 Scope ........................................................................................................................................................5
2 References ................................................................................................................................................5
3 Definitions and abbreviations ...................................................................................................................5
3.1 Definitions .......................................................................................................................................................... 5
3.3 Abbreviations ..................................................................................................................................................... 6
4 General aspects .........................................................................................................................................6
4.1 F1 interface general principles ........................................................................................................................... 6
4.2 F1 interface specification objectives .................................................................................................................. 6
4.3 F1 interface capabilities...................................................................................................................................... 7
4.4 F1 interface characteristics ................................................................................................................................. 7
5 Functions of the F1 interface ....................................................................................................................7
5.1 General ............................................................................................................................................................... 7
5.2 F1-C functions .................................................................................................................................................... 7
5.2.1 F1 interface management function................................................................................................................ 7
5.2.2 System Information management function ................................................................................................... 7
5.2.3 F1 UE context management function............................................................................................................ 7
5.2.4 RRC message transfer function .................................................................................................................... 8
5.2.5 Paging function ............................................................................................................................................. 8
5.2.6 Warning messages information transfer function ......................................................................................... 8
5.3 F1-U functions.................................................................................................................................................... 8
5.3.1 Transfer of user data ..................................................................................................................................... 8
5.3.2 Flow control function.................................................................................................................................... 8
6 Procedures of the F1 interface ..................................................................................................................8
6.1 Control plane procedures.................................................................................................................................... 8
6.1.1 Interface Management procedures ................................................................................................................ 8
6.1.2 Context Management procedures ................................................................................................................. 9
6.1.3 RRC Message Transfer procedures .............................................................................................................. 9
6.1.4 System Information procedures .................................................................................................................... 9
6.1.5 Paging procedures ......................................................................................................................................... 9
6.1.6 Resource Coordination procedure................................................................................................................. 9
6.2 User plane procedures ........................................................................................................................................ 9
7 F1 interface protocol structure .................................................................................................................9
7.1 F1 Control Plane Protocol (F1-C) ...................................................................................................................... 9
7.2 F1 User Plane Protocol (F1-U) ......................................................................................................................... 10
8 Other F1 interface specifications ............................................................................................................10
8.1 NG-RAN F1 interface: layer 1 (3GPP TS 38.471) ........................................................................................... 10
8.2 NG-RAN F1 interface: signalling transport (3GPP TS 38.472) ....................................................................... 10
8.3 NG-RAN F1 interface: F1AP specification (3GPP TS 38.473) ....................................................................... 10
8.4 NG-RAN F1 interface: data transport and transport signalling (3GPP TS 38.474).......................................... 11
8.5 NG-RAN F1 interface: user plane protocol (3GPP TS 38.425) ....................................................................... 11

Annex A (informative): Change history ...............................................................................................12

History ..............................................................................................................................................................13

ETSI
3GPP TS 38.470 version 15.2.0 Release 15 4 ETSI TS 138 470 V15.2.0 (2018-07)

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.

ETSI
3GPP TS 38.470 version 15.2.0 Release 15 5 ETSI TS 138 470 V15.2.0 (2018-07)

1 Scope
The present document is an introduction to the 3GPP TS 38.47x series of technical specifications that define the F1
interface. The F1 interface provides means for interconnecting a gNB-CU and a gNB-DU of a gNB within an NG-RAN,
or for interconnecting a gNB-CU and a gNB-DU of an en-gNB within an E-UTRAN.

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 38.401: "NG-RAN; Architecture Description".

[3] 3GPP TS 38.471: "NG-RAN; F1 layer 1".

[4] 3GPP TS 38.472: "NG-RAN; F1 signalling transport".

[5] 3GPP TS 38.473: "NG-RAN; F1 Application Protocol (FnAP)".

[6] 3GPP TS 38.474: "NG-RAN; F1 data transport".

[7] 3GPP TS 38.425: "NG-RAN; Xn interface user plane protocol".

[8] 3GPP TS 38.300: "NR; Overall description; Stage-2".

[9] 3GPP TS 37.340: "NR; Multi-connectivity; Overall description; Stage-2".

[10] 3GPP TS 38.321: "NR; Medium Access Control (MAC) protocol specification".

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].

en-gNB: as defined in TS 37.340 [9]

gNB-CU: as defined in TS 38.401 [2]

gNB-DU: as defined in TS 38.401 [2]

gNB: as defined in TS 38.300 [8]

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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].

DRB Data Radio Bearers

F1-U F1 User plane interface
F1-C F1 Control plane interface
F1AP F1 Application Protocol
GTP-U GPRS Tunnelling Protocol
IP Internet Protocol
NR-MIB NR-Master Information Block
O&M Operation and Maintenance
PA Paging Area
PF Paging Frame
PO Paging Occasion
QoS Quality of Service
RRC Radio Resource Control
SCTP Stream Control Transmission Protocol
SRB Signalling Radio Bearers
SIB1 System Information Block 1
TNL Transport Network Layer

4 General aspects
This clause captures the F1 interface principles and characteristics.

4.1 F1 interface general principles

The general principles for the specification of the F1 interface are as follows:

- the F1 interface is open;

- the F1 interface supports the exchange of signalling information between the endpoints, in addition the interface
supports data transmission to the respective endpoints;

- from a logical standpoint, the F1 is a point-to-point interface between the endpoints.

NOTE: A point-to-point logical interface should be feasible even in the absence of a physical direct connection
between the endpoints.

- the F1 interface supports control plane and user plane separation;

- the F1 interface separates Radio Network Layer and Transport Network Layer;

- the F1 interface enables exchange of UE associated information and non-UE associated information;

- the F1 interface is designed in a future proof way to fulfil different new requirements, support new services and
new functions;

- one gNB-CU and a set of gNB-DUs are visible to other logical nodes as a gNB or an en-gNB where the gNB
terminates the Xn and the NG interfaces, and the en-gNB terminates the X2 and the S1-U interfaces;

- the gNB-CU may be separated in control plane (CP) and user plane (UP).

4.2 F1 interface specification objectives

The F1 interface specifications facilitate the following:

- inter-connection of a gNB-CU and a gNB-DU supplied by different manufacturers.

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4.3 F1 interface capabilities

4.4 F1 interface characteristics

5 Functions of the F1 interface

5.1 General
The following clauses describe the functions supported over F1-C and F1-U.

5.2 F1-C functions

5.2.1 F1 interface management function
The error indication function is used by the gNB-DU or gNB-CU to indicate to the gNB-CU or gNB-DU that an error
has occurred.

The reset function is used to initialize the peer entity after node setup and after a failure event occurred. This procedure
can be used by both the gNB-DU and the gNB-CU.

The F1 setup function allows to exchange application level data needed for the gNB-DU and gNB-CU to interoperate
correctly on the F1 interface. The F1 setup is initiated by the gNB-DU.

The gNB-CU Configuration Update and gNB-DU Configuration Update functions allow to update application level
configuration data needed between gNB-CU and gNB-DU to interoperate correctly over the F1 interface, and may
activate or deactivate cells.

The F1 setup and gNB-DU Configuration Update functions allow to inform the S-NSSAI(s) supported by the gNB-DU.

The F1 resource coordination function is used to transfer information about frequency resource sharing between gNB-
CU and gNB-DU.

5.2.2 System Information management function

Scheduling of system broadcast information is carried out in the gNB-DU. The gNB-DU is responsible for transmitting
the system information according to the scheduling parameters available.

The gNB-DU is responsible for the encoding of NR-MIB. In case broadcast of SIB1 and other SI messages is needed,
the gNB-DU is responsible for the encoding of SIB1 and the gNB-CU is responsible for the encoding of other SI
messages.

5.2.3 F1 UE context management function

The F1 UE context management function supports the establishment and modification of the necessary overall UE
context.

The establishment of the F1 UE context is initiated by the gNB-CU and accepted or rejected by the gNB-DU based on
admission control criteria (e.g., resource not available).

The modification of the F1 UE context can be initiated by either gNB-CU or gNB-DU. The receiving node can accept
or reject the modification. The F1 UE context management function also supports the release of the context previously
established in the gNB-DU. The release of the context is triggered by the gNB-CU either directly or following a request
received from the gNB-DU. The gNB-CU request the gNB-DU to release the UE Context when the UE enters
RRC_IDLE or RRC_INACTIVE.
This function can be also used to manage DRBs and SRBs, i.e., establishing, modifying and releasing DRB and SRB
resources. The establishment and modification of DRB resources are triggered by the gNB-CU and accepted/rejected by
the gNB-DU based on resource reservation information and QoS information to be provided to the gNB-DU. For each
DRB to be setup or modified, the S-NSSAI may be provided by gNB-CU to the gNB-DU in the UE Context Setup
procedure and the UE Context Modification procedure.

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The mapping between QoS flows and radio bearers is performed by gNB-CU and the granularity of bearer related
management over F1 is radio bearer level. For NG-RAN, the gNB-CU provides an aggregated DRB QoS profile and
QoS flow profile to the gNB-DU, and the gNB-DU either accepts the request or rejects it with appropriate cause value.
To support packet duplication for intra-gNB-DU CA as described in TS 38.300 [8], one data radio bearer should be
configured with two GTP-U tunnels between gNB-CU and a gNB-DU.

With this function, gNB-CU requests the gNB-DU to setup or change of the SpCell (as defined in TS 38.321[10]) for
the UE, and the gNB-DU either accepts or rejects the request with appropriate cause value.

With this function, the gNB-CU requests the setup of the SCell(s) at the gNB-DU side, and the gNB-DU accepts all,
some or none of the SCell(s) and replies to the gNB-CU. The gNB-CU requests the removal of the SCell(s) for the UE.

5.2.4 RRC message transfer function

This function allows to transfer RRC messages between gNB-CU and gNB-DU. RRC messages are transferred over F1-
C. The gNB-CU is responsible for the encoding of the dedicated RRC message with assistance information provided by
gNB-DU.

5.2.5 Paging function

The gNB-DU is responsible for transmitting the paging information according to the scheduling parameters provided.

The gNB-CU provides paging information to enable the gNB-DU to calculate the exact PO and PF. The gNB-CU
determines the PA. The gNB-DU consolidates all the paging records for a particular PO, PF and PA, and encodes the
final RRC message and broadcasts the paging message on the respective PO, PF in the PA.

5.2.6 Warning messages information transfer function

This function allows to cooperate with the warning message transmission procedures over NG interface. The gNB-CU
is responsible for encoding the warning related SI message and sending it together with other warning related
information for the gNB-DU to broadcast over the radio interface.

5.3 F1-U functions

5.3.1 Transfer of user data
This function allows to transfer of user data between gNB-CU and gNB-DU.

5.3.2 Flow control function

This function allows to control the downlink user data flow to the gNB-DU. The detailed protocol is specified in
TS 38.425 [7].

6 Procedures of the F1 interface

6.1 Control plane procedures
6.1.1 Interface Management procedures
The F1 Interface management procedures are listed below:

- Reset procedure

- Error Indication procedure

- F1 Setup procedure

- gNB-DU Configuration Update procedure

- gNB-CU Configuration Update procedure

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3GPP TS 38.470 version 15.2.0 Release 15 9 ETSI TS 138 470 V15.2.0 (2018-07)

6.1.2 Context Management procedures

The F1 Context management procedures are listed below:

- UE Context setup procedure

- UE Context Release Request (gNB-DU initiated) procedure

- UE Context Release (gNB-CU initiated) procedure

- UE Context Modification (gNB-CU initiated) procedure

- UE Context Modification Required (gNB-DU initiated) procedure

- UE Inactivity Notification Procedure

6.1.3 RRC Message Transfer procedures

The F1 RRC message transfer procedures are listed below:

- Initial UL RRC Message Transfer procedure

- UL RRC Message Transfer procedure

- DL RRC Message Transfer procedure

6.1.4 System Information procedures

The F1 System information procedures are listed below:

- System Information Delivery Command procedure

6.1.5 Paging procedures

The F1 Paging procedures are listed below:

- Paging procedure

6.1.6 Resource Coordination procedure

The F1 Resource Coordination procedure is listed below:

- gNB-DU Resource Coordination procedure

6.2 User plane procedures

7 F1 interface protocol structure

7.1 F1 Control Plane Protocol (F1-C)
Figure 7.1-1 shows the protocol structure for F1-C. The TNL is based on IP transport, comprising the SCTP on top of
IP. The application layer signalling protocol is referred to as F1AP (F1 Application Protocol).

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Control Plane
Radio
Network F1AP
Layer

SCTP

Transport IP
Network
Layer Data link layer

Physical layer

Figure 7.1-1: Interface protocol structure for F1-C

7.2 F1 User Plane Protocol (F1-U)

Figure 7.2-1 shows the protocol structure for F1-U. The TNL is based on IP transport, comprising the UDP and GTP-U
on top of IP.

User Plane
Radio
Network
Layer

GTP-U

UDP

Transport IP
Network
Layer Data link layer

Physical layer

Figure 7.2-1: Interface protocol structure for F1-U

8 Other F1 interface specifications

This clause contains the description of the other related 3GPP specifications.

8.1 NG-RAN F1 interface: layer 1 (3GPP TS 38.471)

3GPP TS 38.471 [3] specifies the physical layer technologies that may be used to support the F1 interface.

8.2 NG-RAN F1 interface: signalling transport (3GPP

TS 38.472)
3GPP TS 38.472 [4] specifies the signalling bearers for the F1AP for the F1-C interface.

8.3 NG-RAN F1 interface: F1AP specification (3GPP

TS 38.473)
3GPP TS 38.473 [5] specifies the F1AP protocol for radio network control plane signalling over the F1 interface.

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8.4 NG-RAN F1 interface: data transport and transport

signalling (3GPP TS 38.474)
3GPP TS 38.474 [6] specifies the transport bearers for the user plane of the F1-U interface.

8.5 NG-RAN F1 interface: user plane protocol (3GPP

TS 38.425)
3GPP TS 38.425 [7] specifies the user plane protocol being used over the F1-U interface.

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3GPP TS 38.470 version 15.2.0 Release 15 12 ETSI TS 138 470 V15.2.0 (2018-07)

Annex A (informative):
Change history
Change history
Date Meeting TDoc CR Rev Cat Subject/Comment New
version
2017-06 R3 NR#2 R3-172492 - - - First version 0.1.0
2017-07 R3 NR#2 R3-172639 - - - Incorporated agreed TPs from R3 NR#2 Adhoc 0.2.0
2017-08 R3#97 R3-173450 - - - Incorporated agreed TPs from R3#97 0.3.0
2017-10 R3#97b R3-174244 - - - Incorporated agreed TPs from R3#97b 0.4.0
2017-10 R3#97b R3-174259 Merged text from TS 38.401 v040 0.4.1
2017-12 R3#98 R3-175060 Incorporated agreed TPs from R3#98 0.5.0
2017-12 RAN#78 RP-172286 Submitted for approval to RAN 1.0.0
2018-01 RP-78 TS approved by RAN plenary 15.0.0
2018-03 RP-79 RP-180468 0002 - F UE Context Management Procedure Related with EN-DC Operation 15.1.0
- Stage 2
2018-03 RP-79 RP-180468 0006 - B Correction of packet duplication 15.1.0
2018-03 RP-79 RP-180468 0007 1 B SCell management 15.1.0
2018-06 RP-80 RP-181237 0003 6 B Introduction of SA NR (38.470 Baseline CR covering RAN3 15.2.0
agreements)
2018-06 RP-80 RP-181238 0008 3 F Adding new F1 procedure for UE Inactivity Notification 15.2.0
2018-06 RP-80 RP-181237 0010 - B Introduction of LTE-NR coexistence function 15.2.0

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3GPP TS 38.470 version 15.2.0 Release 15 13 ETSI TS 138 470 V15.2.0 (2018-07)

History
Document history
V15.2.0 July 2018 Publication

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