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TECHNICAL SPECIFICATION
5G;
NR;
Radio Link Control (RLC) protocol specification
(3GPP TS 38.322 version 15.4.0 Release 15)
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3GPP TS 38.322 version 15.4.0 Release 15 1 ETSI TS 138 322 V15.4.0 (2019-04)
Reference
RTS/TSGR-0238322vf40
Keywords
5G
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3GPP TS 38.322 version 15.4.0 Release 15 2 ETSI TS 138 322 V15.4.0 (2019-04)
Intellectual Property Rights
Essential patents
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pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
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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 38.322 version 15.4.0 Release 15 3 ETSI TS 138 322 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, symbols and abbreviations . 6
3.1 Definitions . 6
3.2 Abbreviations . 6
4 General . 7
4.1 Introduction . 7
4.2 RLC architecture . 7
4.2.1 RLC entities . 7
4.2.1.1 TM RLC entity . 8
4.2.1.1.1 General . 8
4.2.1.1.2 Transmitting TM RLC entity . 9
4.2.1.1.3 Receiving TM RLC entity . 9
4.2.1.2 UM RLC entity . 9
4.2.1.2.1 General . 9
4.2.1.2.2 Transmitting UM RLC entity . 10
4.2.1.2.3 Receiving UM RLC entity . 10
4.2.1.3 AM RLC entity . 10
4.2.1.3.1 General . 10
4.2.1.3.2 Transmitting side . 11
4.2.1.3.3 Receiving side . 12
4.3 Services . 12
4.3.1 Services provided to upper layers . 12
4.3.2 Services expected from lower layers . 12
4.4 Functions . 12
5 Procedures . 12
5.1 RLC entity handling . 12
5.1.1 RLC entity establishment . 12
5.1.2 RLC entity re-establishment . 13
5.1.3 RLC entity release . 13
5.2 Data transfer procedures . 13
5.2.1 TM data transfer . 13
5.2.1.1 Transmit operations . 13
5.2.1.1.1 General . 13
5.2.1.2 Receive operations . 13
5.2.1.2.1 General . 13
5.2.2 UM data transfer . 13
5.2.2.1 Transmit operations . 13
5.2.2.1.1 General . 13
5.2.2.2 Receive operations . 13
5.2.2.2.1 General . 13
5.2.2.2.2 Actions when an UMD PDU is received from lower layer . 14
5.2.2.2.3 Actions when an UMD PDU is placed in the reception buffer . 14
5.2.2.2.4 Actions when t-Reassembly expires . 15
5.2.3 AM data transfer . 15
5.2.3.1 Transmit operations . 15
5.2.3.1.1 General . 15
5.2.3.2 Receive operations . 16
5.2.3.2.1 General . 16
5.2.3.2.2 Actions when an AMD PDU is received from lower layer . 16
ETSI
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3GPP TS 38.322 version 15.4.0 Release 15 4 ETSI TS 138 322 V15.4.0 (2019-04)
5.2.3.2.3 Actions when an AMD PDU is placed in the reception buffer . 16
5.2.3.2.4 Actions when t-Reassembly expires . 17
5.3 ARQ procedures . 17
5.3.1 General . 17
5.3.2 Retransmission . 17
5.3.3 Polling . 18
5.3.3.1 General . 18
5.3.3.2 Transmission of a AMD PDU . 18
5.3.3.3 Reception of a STATUS report . 19
5.3.3.4 Expiry of t-PollRetransmit . 19
5.3.4 Status reporting . 19
5.4 SDU discard procedures . 20
5.5 Data volume calculation . 21
5.6 Handling of unknown, unforeseen and erroneous protocol data . 21
5.6.1 Reception of PDU with reserved or invalid values . 21
6 Protocol data units, formats and parameters . 21
6.1 Protocol data units . 21
6.1.1 General . 21
6.1.2 RLC data PDU . 21
6.1.3 RLC control PDU . 21
6.2 Formats and parameters . 21
6.2.1 General . 21
6.2.2 Formats . 22
6.2.2.1 General . 22
6.2.2.2 TMD PDU . 22
6.2.2.3 UMD PDU . 22
6.2.2.4 AMD PDU . 23
6.2.2.5 STATUS PDU . 24
6.2.3 Parameters. 26
6.2.3.1 General . 26
6.2.3.2 Data field . 26
6.2.3.3 Sequence Number (SN) field . 26
6.2.3.4 Segmentation Info (SI) field . 26
6.2.3.5 Segment Offset (SO) field . 26
6.2.3.6 Data/Control (D/C) field . 26
6.2.3.7 Polling bit (P) field . 27
6.2.3.8 Reserved (R) field . 27
6.2.3.9 Control PDU Type (CPT) field . 27
6.2.3.10 Acknowledgement SN (ACK_SN) field . 27
6.2.3.11 Extension bit 1 (E1) field . 27
6.2.3.12 Negative Acknowledgement SN (NACK_SN) field . 28
6.2.3.13 Extension bit 2 (E2) field . 28
6.2.3.14 SO start (SOstart) field . 28
6.2.3.15 SO end (SOend) field . 28
6.2.3.16 Extension bit 3 (E3) field . 28
6.2.3.17 NACK range field . 29
7 Variables, constants and timers . 29
7.1 State variables . 29
7.2 Constants . 30
7.3 Timers . 31
7.4 Configurable parameters . 31
Annex A (informative): Change history . 32
History . 33
ETSI
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3GPP TS 38.322 version 15.4.0 Release 15 5 ETSI TS 138 322 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 38.322 version 15.4.0 Release 15 6 ETSI TS 138 322 V15.4.0 (2019-04)
1 Scope
The present document specifies the NR Radio Link Control (RLC) protocol for the UE – NR 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 38.321: "NR MAC protocol specification".
[4] 3GPP TS 38.323: "NR PDCP specification".
[5] 3GPP TS 38.331: "NR RRC Protocol specification"
3 Definitions, symbols 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].
Data field element: An RLC SDU or an RLC SDU segment that is mapped to the Data field.
RLC data volume: The amount of data available for transmission in an RLC entity.
RLC SDU segment: A segment of an RLC SDU.
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in 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
TR 21.905 [1].
AM Acknowledged Mode
AMD AM Data
ARQ Automatic Repeat request
gNB NR Node B
PDU Protocol Data Unit
RLC Radio Link Control
SDU Service Data Unit
SN Sequence Number
TB Transport Block
TM Transparent Mode
TMD TM Data
UE User Equipment
UM Unacknowledged Mode
UMD UM Data
ETSI
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3GPP TS 38.322 version 15.4.0 Release 15 7 ETSI TS 138 322 V15.4.0 (2019-04)
4 General
4.1 Introduction
The objective is to describe the RLC architecture and the RLC entities from a functional point of view.
4.2 RLC architecture
4.2.1 RLC entities
The description in this sub clause is a model and does not specify or restrict implementations.
RRC is generally in control of the RLC configuration.
Functions of the RLC sub layer are performed by RLC entities. For an RLC entity configured at the gNB, there is a peer
RLC entity configured at the UE and vice versa.
An RLC entity receives/delivers RLC SDUs from/to upper layer and sends/receives RLC PDUs to/from its peer RLC
entity via lower layers.
An RLC PDU can either be an RLC data PDU or an RLC control PDU. If an RLC entity receives RLC SDUs from
upper layer, it receives them through a single RLC channel between RLC and upper layer, and after forming RLC data
PDUs from the received RLC SDUs, the RLC entity submits the RLC data PDUs to lower layer through a single logical
channel. If an RLC entity receives RLC data PDUs from lower layer, it receives them through a single logical channel,
and after forming RLC SDUs from the received RLC data PDUs, the RLC entity delivers the RLC SDUs to upper layer
through a single RLC channel between RLC and upper layer. If an RLC entity submits/receives RLC control PDUs
to/from lower layer, it submits/receives them through the same logical channel it submits/receives the RLC data PDUs
through.
An RLC entity can be configured to perform data transfer in one of the following three modes: Transparent Mode (TM),
Unacknowledged Mode (UM) or Acknowledged Mode (AM). Consequently, an RLC entity is categorized as a TM
RLC entity, an UM RLC entity or an AM RLC entity depending on the mode of data transfer that the RLC entity is
configured to provide.
A TM RLC entity is configured either as a transmitting TM RLC entity or a receiving TM RLC entity. The transmitting
TM RLC entity receives RLC SDUs from upper layer and sends RLC PDUs to its peer receiving TM RLC entity via
lower layers. The receiving TM RLC entity delivers RLC SDUs to upper layer and receives RLC PDUs from its peer
transmitting TM RLC entity via lower layers.
An UM RLC entity is configured either as a transmitting UM RLC entity or a receiving UM RLC entity. The
transmitting UM RLC entity receives RLC SDUs from upper layer and sends RLC PDUs to its peer receiving UM RLC
entity via lower layers. The receiving UM RLC entity delivers RLC SDUs to upper layer and receives RLC PDUs from
its peer transmitting UM RLC entity via lower layers.
An AM RLC entity consists of a transmitting side and a receiving side. The transmitting side of an AM RLC entity
receives RLC SDUs from upper layer and sends RLC PDUs to its peer AM RLC entity via lower layers. The receiving
side of an AM RLC entity delivers RLC SDUs to upper layer and receives RLC PDUs from its peer AM RLC entity via
lower layers.
Figure 4.2.1-1 illustrates the overview model of the RLC sub layer.
ETSI
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3GPP TS 38.322 version 15.4.0 Release 15 8 ETSI TS 138 322 V15.4.0 (2019-04)
upper layer
RLC channel
transmitting receiving transmitting receiving
AM RLC entity
gNB
TM RLC entity TM RLC entity UM RLC entity UM RLC entity
logical
channel
lower layers
radio interface
lower layers
logical
channel
receiving transmitting receiving transmitting
AM RLC entity
UE
TM RLC entity TM RLC entity UM RLC entity UM RLC entity
RLC channel
upper layer
Figure 4.2.1-1: Overview model of the RLC sub layer
RLC SDUs of variable sizes which are byte aligned (i.e. multiple of 8 bits) are supported for all RLC entity types (i.e.
TM, UM and AM RLC entity).
Each RLC SDU is used to construct an RLC PDU without waiting for notification from the lower layer (i.e., by MAC)
of a transmission opportunity. In the case of UM and AM RLC entities, an RLC SDU may be segmented and
transported using two or more RLC PDUs based on the notification(s) from the lower layer.
RLC PDUs are submitted to lower layer only when a transmission opportunity has been notified by lower layer (i.e. by
MAC).
NOTE: The UE should aim to prevent excessive non-consecutive RLC PDUs in a MAC PDU when the UE is
requested to generate more than one MAC PDU.
Description of different RLC entity types are provided below.
4.2.1.1 TM RLC entity
4.2.1.1.1 General
A TM RLC entity can be configured to submit/receive RLC PDUs through the following logical channels:
- BCCH, DL/UL CCCH, and PCCH
ETSI
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