5 F1 Interface user plane protocol
38.4743GPPF1 data transportNG-RANRelease 17TS
5.1 General
The transport layer for data streams over F1 is an IP based Transport. The following figure shows the transport protocol stacks over F1.
Figure 5.1: Transport network layer for data streams over F1
The GTP-U (TS 29.281 [2]) protocol over UDP over IP shall be supported as the transport for data streams on the F1 interface. The data link layer is as specified in clause 4.
The transport bearer is identified by the GTP-U TEID (TS 29.281 [2]) and the IP address (source TEID, destination TEID, source IP address, destination IP address).
5.2 GTP-U
The GTP-U (TS 29.281 [2]) protocol shall be used over the F1 interface between gNB-DU and gNB-CU.
5.3 UDP/IP
The path protocol used shall be UDP (IETF RFC 768 [3]).
The UDP port number for GTP-U shall be as defined in TS 29.281 [2].
The gNB-DU and the gNB-CU shall support fragmentation and assembly of GTP packets at the IP layer.
The gNB-DU and the gNB-CU shall support Ipv6 (IETF RFC 8200 [5]) and/or Ipv4 (IETF RFC 791 [6]).
There may be one or several IP addresses in the gNB-DU and in the gNB-CU. The packet processing function in the gNB-CU shall send downstream packets of a given bearer to the gNB-DU IP address (received in F1AP) associated to that particular bearer. The packet processing function in the gNB-DU shall send upstream packets of a given bearer to the gNB-CU IP address (received in F1AP) associated to that particular bearer.
The Transport Layer Address signalled in F1AP messages is a bit string of:
a) 32 bits in case of Ipv4 address according to IETF RFC 791 [6]; or
b) 128 bits in case of Ipv6 address according to IETF RFC 8200 [5]; or
c) 160 bits if both Ipv4 and Ipv6 addresses are signalled, in which case the Ipv4 address is contained in the first 32 bits.
5.4 Diffserv code point marking
IP Differentiated Services code point marking (IETF RFC 2474 [4]) shall be supported. Except the downlink F1-U to the IAB node, the mapping between traffic categories and Diffserv code points shall be configurable by O&M based on 5G QoS Identifier (5QI) , the Priority Level (if explicitly signalled), and other NG-RAN traffic parameters (e.g. ARP). Traffic categories are implementation-specific and may be determined from the application parameters. In the IAB system, the Diffserv code points used for the downlink F1-U shall be configurable by the CU-CP based on the O&M-configured mapping between traffic categories and Diffserv code points.
Annex A (informative):
Change history
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Change history |
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Date |
Meeting |
Tdoc |
CR |
Rev |
Cat |
Subject/Comment |
New version |
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2017-6 |
RAN3 NR ad hoc |
The first version, includes technical content endorsed in previous meetings |
0.1.0 |
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2017-9 |
RAN3#97bis |
R3-173796 |
Rapporteur’s update, minor correction |
0.2.0 |
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2017-10 |
RAN3#97bis |
R3-174248 |
TS 38.474 v0.3.0 covering agreements of RAN3 #97bis |
0.3.0 |
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2017-12 |
RAN3#98 |
R3-175075 |
Baseline pCR to TS 38.474 covering agreements of RAN3#98 |
0.4.0 |
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2017-12 |
RAN#78 |
RP-172671 |
First submission to RAN for approval |
1.0.0 |
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2018-01 |
RP-78 |
TS approved by RAN plenary |
15.0.0 |
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2018-06 |
RP-80 |
RP-181238 |
0002 |
F |
Rapporteur’s correction to TS 38.474 |
15.1.0 |
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2018-09 |
RP-81 |
RP-181920 |
0004 |
– |
F |
Updated reference to IPv6 |
15.2.0 |
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2019-09 |
RP-85 |
RP-192166 |
0006 |
1 |
F |
Correction of DSCP Derivation |
15.3.0 |
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2020-07 |
RP-88-e |
RP-201077 |
0007 |
4 |
B |
Support for IAB |
16.0.0 |
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2020-12 |
RP-90-e |
RP-202310 |
0008 |
1 |
F |
Correction in F1-U on DSCP Derivation in IAB-donor node |
16.1.0 |
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2022-03 |
SA#95-e |
Promotion to Release 17 without technical change |
17.0.0 |
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