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TECHNICAL SPECIFICATION
5G;
NG-RAN;
NR user plane protocol
(3GPP TS 38.425 version 15.4.0 Release 15)
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3GPP TS 38.425 version 15.4.0 Release 15 1 ETSI TS 138 425 V15.4.0 (2019-04)
Reference
RTS/TSGR-0338425vf40
Keywords
5G
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3GPP TS 38.425 version 15.4.0 Release 15 2 ETSI TS 138 425 V15.4.0 (2019-04)
Intellectual Property Rights
Essential patents
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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.
The cross reference between GSM, UMTS, 3GPP and ETSI identities can be found under
.
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
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3GPP TS 38.425 version 15.4.0 Release 15 3 ETSI TS 138 425 V15.4.0 (2019-04)
Contents
Intellectual Property Rights . 2
Foreword . 2
Modal verbs terminology . 2
Foreword . 5
1 Scope . 6
2 References . 6
3 Definitions and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 6
4 General . 7
4.1 General aspects . 7
5 NR user plane protocol . 7
5.1 General . 7
5.2 NR user plane protocol layer services . 7
5.3 Services expected from the Transport Network Layer . 8
5.4 Elementary procedures . 9
5.4.1 Transfer of Downlink User Data . 9
5.4.1.1 Successful operation. 9
5.4.1.2 Unsuccessful operation . 9
5.4.2 Downlink Data Delivery Status . 10
5.4.2.1 Successful operation. 10
5.4.2.2 Unsuccessful operation . 11
5.4.3 Transfer of Assistance Information . 11
5.4.3.1 Successful operation. 11
5.5 Elements for the NR user plane protocol . 12
5.5.1 General . 12
5.5.2 Frame format for the NR user plane protocol . 13
5.5.2.1 DL USER DATA (PDU Type 0) . 13
5.5.2.2 DL DATA DELIVERY STATUS (PDU Type 1) . 13
5.5.2.3 ASSISTANCE INFORMATION DATA (PDU Type 2) . 14
5.5.3 Coding of information elements in frames . 15
5.5.3.1 PDU Type . 15
5.5.3.2 Spare . 15
5.5.3.3 Report polling . 15
5.5.3.4 NR-U Sequence Number . 16
5.5.3.5 Desired buffer size for the data radio bearer . 16
5.5.3.6 Desired Data Rate . 16
5.5.3.7 DL Flush . 16
5.5.3.8 DL discard NR PDCP PDU SN . 16
5.5.3.9 DL Discard Blocks . 16
5.5.3.10 DL discard NR PDCP PDU SN start . 16
5.5.3.11 DL discard Number of blocks . 16
5.5.3.12 Discarded Block size . 17
5.5.3.13 Lost Packet Report . 17
5.5.3.14 Final Frame Indication . 17
5.5.3.15 Number of lost NR-U Sequence Number ranges reported . 17
5.5.3.16 Start of lost NR-U Sequence Number range . 17
5.5.3.17 End of lost NR-U Sequence Number range . 17
5.5.3.18 Highest Delivered NR PDCP SN Ind . 17
5.5.3.19 Highest successfully delivered NR PDCP Sequence Number . 17
5.5.3.20 Highest Transmitted NR PDCP SN Ind . 18
5.5.3.21 Highest transmitted NR PDCP Sequence Number . 18
5.5.3.22 Cause Report . 18
5.5.3.23 Cause Value . 18
ETSI
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3GPP TS 38.425 version 15.4.0 Release 15 4 ETSI TS 138 425 V15.4.0 (2019-04)
5.5.3.24 Padding . 18
5.5.3.28 Void. 18
5.5.3.29 Retransmission flag . 18
5.5.3.30 Delivered Retransmitted NR PDCP SN Ind . 18
5.5.3.31 Retransmitted NR PDCP SN Ind . 19
5.5.3.32 Successfully delivered retransmitted NR PDCP Sequence Number . 19
5.5.3.33 Retransmitted NR PDCP Sequence Number . 19
5.5.3.34 Data Rate Indication . 19
5.5.3.35 PDCP Duplication Indication . 19
5.5.3.36 PDCP Duplication Activation Suggestion . 19
5.5.3.37 Number of Assistance Information Field . 19
5.5.3.38 Assistance Information Type . 20
5.5.3.39 Radio Quality Assistance Information . 20
5.5.3.40 Assistance Information Report Polling Flag . 20
5.5.3.41 Report Delivered . 20
5.5.3.42 DL report NR PDCP PDU SN . 20
5.5.3.43 User data existence flag . 20
5.5.3.44 Number of octets for Radio Quality Assistance Information Field . 20
5.5.3.45 Assistance Information Indication . 21
5.5.4 Timers . 21
5.6 Handling of unknown, unforeseen and erroneous protocol data . 21
Annex A (informative): Example of using future Extension . 22
A.1 Example of using Future Extension field . 22
A.1.1 New IE Flags . 22
Annex B (informative): Change history . 23
History . 24
ETSI
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3GPP TS 38.425 version 15.4.0 Release 15 5 ETSI TS 138 425 V15.4.0 (2019-04)
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
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3GPP TS 38.425 version 15.4.0 Release 15 6 ETSI TS 138 425 V15.4.0 (2019-04)
1 Scope
The present document specifies the NR user plane protocol functions used within NG-RAN and, for EN-DC, within E-
UTRAN. NR user plane protocol functions may reside in nodes terminating either the X2-U (for EN-DC) or the Xn-U
or the F1-U 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 29.281: "General Packet Radio System (GPRS) Tunnelling Protocol User Plane
(GTPv1-U)".
[3] 3GPP TS 37.340: "NR; Multi-connectivity; Overall description; Stage-2".
[4] 3GPP TS 36.321: "Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access
Control (MAC) protocol specification".
[5] 3GPP TS 38.321: "NR; Medium Access Control (MAC) protocol specification".
[6] 3GPP TS 36.322: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control
(RLC) protocol specification".
[7] 3GPP TS 38.322: "NR; Radio Link Control (RLC) 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].
Corresponding node: a node interacting with a node hosting NR PDCP for flow control.
Master node: as defined in TS 37.340 [3].
Secondary node: as defined in TS 37.340 [3].
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].
EN-DC E-UTRA-NR Dual Connectivity
MR-DC Multi-RAT Dual Connectivity
ETSI
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3GPP TS 38.425 version 15.4.0 Release 15 7 ETSI TS 138 425 V15.4.0 (2019-04)
4 General
4.1 General aspects
The NR user plane protocol is located in the User Plane of the Radio Network layer over either the Xn or the X2 or the
F1 interface.
The NR user plane protocol is used to convey control information related to the user data flow management of data
radio bearers.
Each NR user plane protocol instance is associated to one data radio bearer only. There is one NR user plane instance
per GTP tunnel. When a GTP tunnel is set up, a new NR user plane instance is set up.
If configured, NR user plane protocol instances exist at the Master node and the Secondary node in the context of DC or
at nodes hosting F1-U protocol terminations. The NR user plane protocol supports direct communication between NR
user plane protocol entities, regardless of whether they terminate the same or different user plane interfaces.
NOTE: User data radio bearers may be setup for data forwarding purposes during Xn HO or during DC related
mobility without requiring the execution of any additional data radio bearer related user plane protocol
functions related to an NR user plane protocol instance.
On each data radio bearer, the NR user plane protocol operates with RLC AM or RLC UM.
In this version of the present document, NR user plane protocol data is conveyed by GTP-U protocol means, more
specifically, by means of the "NR RAN Container" GTP-U extension header as defined in TS 29.281 [2].
5 NR user plane protocol
5.1 General
The NR user plane protocol layer is using services of the transport network layer in order to allow flow control of user
data packets transferred from the node hosting NR PDCP to the corresponding node.
5.2 NR user plane protocol layer services
The following functions are provided by the NR user plane protocol:
- Provision of NR user plane specific sequence number information for user data transferred from the node hosting
NR PDCP to the corresponding node for a specific data radio bearer.
- Information of successful in sequence delivery of NR PDCP PDUs to the UE from the corresponding node for
user data associated with a specific data radio bearer.
- Information of NR PDCP PDUs that were not delivered to the UE or not transmitted to the lower layers.
- Information of NR PDCP PDUs transmitted to the lower layers for user data associated with a specific data radio
bearer.
- Information of downlink NR PDCP PDUs to be discarded for user data associated with a specific data radio
bearer;
- Information of the currently desired buffer size at the corresponding node for transmitting to the UE user data
associated with a specific data radio bearer.
- Information of the currently desired data rate in bytes at the corresponding node for transmitting to the UE user
data associated with a specific data radio bearer;
- Information of successful in sequence delivery of NR PDCP PDUs to the UE from the corresponding node for
retransmission user data associate with a specific data radio bearer;
- Information of NR PDCP PDUs transmitted to the lower layers for retransmission user data associated with a
specific data radio bearer.
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3GPP TS 38.425 version 15.4.0 Release 15 8 ETSI TS 138 425 V15.4.0 (2019-04)
- Information of the specific events at the corresponding node.
- Information on Radio Link Quality from the corresponding node for user data associated with a specific data
radio bearer.
5.3 Services expected from the Transport Network Layer
The NR user plane protocol layer expects the following services from the Transport Network Layer:
- Transfer of user data.
ETSI
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3GPP TS 38.425 version 15.4.0 Release 15 9 ETSI TS 138 425 V15.4.0 (2019-04)
5.4 Elementary procedures
5.4.1 Transfer of Downlink User Data
5.4.1.1 Successful operation
The purpose of the Transfer of Downlink User Data procedure is to provide NR-U specific sequence number
information at the transfer of user data carrying a DL NR PDCP PDU from the node hosting the NR PDCP entity to the
corresponding node.
An NR user plane protocol instance making use of the Transfer of Downlink User Data procedure is associated to a
single data radio bearer only.
The node hosting the NR PDCP entity shall assign consecutive NR-U sequence numbers to each transferred NR-U
packet. A retransmitted NR PDCP PDU shall be assigned a new NR-U sequence number.
The node hosting the NR PDCP entity indicates to the corresponding node whether this NR-U packet is a
retransmission of NR PDCP PDU.
The node hosting the NR PDCP entity can indicate to the corresponding node to either discard all NR PDCP PDUs up
to and including a defined DL discard NR PDCP PDU SN or discard one or a number of blocks of downlink NR PDCP
PDUs.
If the Assistance Information Report Polling Flag is equal to 1, the corresponding node shall, if supported, send the
ASSISTANCE INFORMATION DATA to the node hosting the NR PDCP entity.
The corresponding node shall detect whether an NR-U packet was lost and memorise the respective sequence number
after it has declared the respective NR-U packet as being "lost".
The corresponding node shall transfer the remaining NR PDCP PDUs towards the UE and memorise the highest NR
PDCP PDU sequence number of the NR PDCP PDU that was successfully delivered (as defined in TS 36.322 [6] and
TS 38.322 [7]) in sequence towards the UE (in case RLC AM is used) and the highest NR PDCP PDU sequence
number of the NR PDCP PDU that was transmitted to the lower layers.
The corresponding node shall send the DL DATA DELIVERY STATUS if the Report Polling Flag is set to 1 or when
the NR PDCP PDU with the indicated DL report NR PDCP PDU SN has been successfully delivered, unless a situation
of overload at the corresponding node is encountered. The DL DATA DELIVERY STATUS sent as a response to a
specific DL report NR PDCP PDU SN shall be sent only when all PDCP PDU SNs up to this DL report NR PDCP PDU
have been successfully delivered in-sequence.
NOTE: The Transfer of Downlink User Data procedure and the associated feedback of lost NR-U packets assist
the node hosting the NR PDCP entity in avoiding NR PDCP HFN de-synchronisation. If a deployment
decides to not use the Transfer of Downlink User Data procedure, NR PDCP HFN synchronization
should be ensured by other means.
If the User data existence flag is set to 1, the corresponding node assumes that the node hosting the NR PDCP entity has
some user data for the concerned data radio bearer. The corresponding node decides whether and when to use DRX for
the UE (i.e. the corresponding node may indicate the UE to use DRX even if the flag is set to 1 and the received DL
USER DATA frame contains no user data).
node hosting corresponding
NR PDCP node
DL USER DATA
Figure 5.4.1.1-1: Successful Transfer of Downlink User Data
5.4.1.2 Unsuccessful operation
Void.
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3GPP TS 38.425 version 15.4.0 Release 15 10 ETSI TS 138 425 V15.4.0 (2019-04)
5.4.2 Downlink Data Delivery Status
5.4.2.1 Successful operation
The purpose of the Downlink Data Delivery Status procedure is to provide feedback from the corresponding node to the
node hosting the NR PDCP entity to allow the node hosting the NR PDCP entity to control the downlink user data flow
via the corresponding node for the respective data radio bearer. The corresponding node may also transfer uplink user
data for the concerned data radio bearer to the node hosting the NR PDCP entity together with a DL DATA
DELIVERY STATUS frame within the same GTP-U PDU.
The Downlink Data Delivery Status procedure is also used to provide feedback from the corresponding node to the
node hosting the NR PDCP entity to allow the node hosting the NR PDCP entity to control the successful delivery of
DL control data to the corresponding node.
When the corresponding node decides to trigger the feedback for Downlink Data Delivery procedure it shall report as
specified in section 5.2:
a) in case of RLC AM, the highest NR PDCP PDU sequence number successfully delivered in sequence to the UE
among those NR PDCP PDUs received from the node hosting the NR PDCP entity i.e. excludes those
retransmission NR PDCP PDUs;
b) the desired buffer size in bytes for the concerned data radio bearer;
c) optionally, the desired data rate in bytes associated with a specific data radio bearer configured for the UE;
d) the NR-U packets that were declared as being "lost" by the corresponding node and have not yet been reported to
the node hosting the NR PDCP entity within the DL DATA DELIVERY STATUS frame;
e) if retransmission NR PDCP PDUs have been delivered, the NR PDCP PDU sequence number associated with
the highest NR-U sequence number among the retransmission NR PDCP PDUs successfully delivered to the UE
in sequence of NR-U sequence number;
f) if retransmission NR PDCP PDUs have been transmitted to the lower layers
...