ETSI TS 136 321 V19.2.0 (2026-04)

LTE; Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification (3GPP TS 36.321 version 19.2.0 Release 19)

RTS/TSGR-0236321vj20

General Information

• Status: Not Published
• Technical Committee: 3GPP RAN 2 - Radio layer 2 specification and Radio layer 3 RR specification
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 02-Apr-2026

Standards Content (Sample)

TECHNICAL SPECIFICATION
LTE;
Evolved Universal Terrestrial Radio Access (E-UTRA);
Medium Access Control (MAC) protocol specification
(3GPP TS 36.321 version 19.2.0 Release 19)

3GPP TS 36.321 version 19.2.0 Release 19 1 ETSI TS 136 321 V19.2.0 (2026-04)

Reference
RTS/TSGR-0236321vj20
Keywords
LTE
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ETSI
3GPP TS 36.321 version 19.2.0 Release 19 2 ETSI TS 136 321 V19.2.0 (2026-04)
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3GPP TS 36.321 version 19.2.0 Release 19 3 ETSI TS 136 321 V19.2.0 (2026-04)
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 . 12
4 General . 14
4.1 Introduction . 14
4.2 MAC architecture . 14
4.2.1 MAC Entities . 14
4.3 Services . 17
4.3.1 Services provided to upper layers . 17
4.3.2 Services expected from physical layer . 17
4.4 Functions . 17
4.5 Channel structure . 18
4.5.1 Transport Channels . 18
4.5.2 Logical Channels . 18
4.5.3 Mapping of Transport Channels to Logical Channels . 19
4.5.3.1 Uplink mapping . 19
4.5.3.2 Downlink mapping . 19
4.5.3.3 Sidelink mapping . 20
5 MAC procedures . 21
5.1 Random Access procedure . 21
5.1.1 Random Access Procedure initialization . 21
5.1.2 Random Access Resource selection . 24
5.1.3 Random Access Preamble transmission . 26
5.1.4 Random Access Response reception. 27
5.1.5 Contention Resolution . 31
5.1.6 Completion of the Random Access procedure . 33
5.1a CB-Msg3-EDT Procedure . 34
5.1a.1 CB-Msg3-EDT initialization . 34
5.1a.2 CB-Msg3 transmission . 35
5.1a.3 CB-Msg4 reception . 36
5.2 Maintenance of Uplink Time Alignment . 37
5.2a Maintenance of UL Synchronization . 39
5.3 DL-SCH data transfer . 39
5.3.1 DL Assignment reception . 39
5.3.2 HARQ operation . 42
5.3.2.1 HARQ Entity. 42
5.3.2.2 HARQ process . 43
5.3.3 Disassembly and demultiplexing . 44
5.4 UL-SCH data transfer . 44
5.4.1 UL Grant reception . 44
5.4.2 HARQ operation . 48
5.4.2.1 HARQ entity . 48
5.4.2.2 HARQ process . 51
5.4.3 Multiplexing and assembly . 54
5.4.3.1 Logical channel prioritization . 54
5.4.3.2 Multiplexing of MAC Control Elements and MAC SDUs . 56
5.4.4 Scheduling Request. 56
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5.4.5 Buffer Status Reporting . 58
5.4.5a Data Volume and Power Headroom Reporting . 60
5.4.6 Power Headroom Reporting . 60
5.4.7 Preconfigured Uplink Resource . 63
5.4.7.1 Transmission using PUR . 63
5.4.7.2 Maintenance of PUR Uplink Time Alignment . 64
5.4.8 Access Stratum Release Assistance Indication . 65
5.4.9 Timing Advance Reporting . 65
5.4.10 GNSS Validity Duration Reporting . 66
5.5 PCH reception . 66
5.6 BCH reception . 66
5.7 Discontinuous Reception (DRX) . 66
5.7a Discontinuous Reception (DRX) for SC-PTM . 71
5.8 MAC reconfiguration . 72
5.9 MAC Reset . 72
5.10 Semi-Persistent Scheduling . 73
5.10.1 Downlink . 74
5.10.2 Uplink . 74
5.11 Handling of unknown, unforeseen and erroneous protocol data . 75
5.12 MCH reception . 76
5.13 Activation/Deactivation of SCells . 76
5.14 SL-SCH Data transfer . 78
5.14.1 SL-SCH Data transmission . 78
5.14.1.1 SL Grant reception and SCI transmission . 78
5.14.1.2 Sidelink HARQ operation . 84
5.14.1.2.1 Sidelink HARQ Entity . 84
5.14.1.2.2 Sidelink process . 84
5.14.1.3 Multiplexing and assembly . 85
5.14.1.3.1 Logical channel prioritization . 85
5.14.1.3.2 Multiplexing of MAC SDUs . 86
5.14.1.4 Buffer Status Reporting . 86
5.14.1.5 TX carrier (re-)selection for V2X sidelink communication . 88
5.14.2 SL-SCH Data reception . 89
5.14.2.1 SCI reception. 89
5.14.2.2 Sidelink HARQ operation . 90
5.14.2.2.1 Sidelink HARQ Entity . 90
5.14.2.2.2 Sidelink process . 90
5.14.2.3 Disassembly and demultiplexing . 91
5.15 SL-DCH data transfer . 91
5.15.1 SL-DCH data transmission . 91
5.15.1.1 Resource allocation . 91
5.15.1.2 Sidelink HARQ operation . 91
5.15.1.2.1 Sidelink HARQ Entity . 91
5.15.1.2.2 Sidelink process . 92
5.15.2 SL-DCH data reception . 93
5.15.2.1 Sidelink HARQ operation . 93
5.15.2.1.1 Sidelink HARQ Entity . 93
5.15.2.1.2 Sidelink process . 93
5.16 SL-BCH data transfer . 94
5.16.1 SL-BCH data transmission . 94
5.16.2 SL-BCH data reception . 94
5.17 Data inactivity monitoring . 94
5.18 Recommended Bit Rate . 94
5.19 Activation/Deactivation of CSI-RS resources . 95
5.20 Preallocated uplink grant . 95
5.21 SC-PTM Stop Indication . 95
5.22 Entering Dormant SCell state . 96
5.23 Autonomous Uplink . 97
5.24 Activation/Deactivation of PDCP duplication. 98
5.25 Transmission of Downlink Channel Quality Report . 98
5.26 Update of Differential Koffset . 99
5.27 GNSS measurement . 99
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5.28 UL Transmission Extension . 99
6 Protocol Data Units, formats and parameters . 99
6.1 Protocol Data Units . 99
6.1.1 General . 99
6.1.2 MAC PDU (DL-SCH and UL-SCH except transparent MAC and Random Access Response, MCH,
CB-Msg4) . 100
6.1.3 MAC Control Elements . 101
6.1.3.1 Buffer Status Report MAC Control Elements . 101
6.1.3.1a Sidelink BSR MAC Control Elements . 104
6.1.3.2 C-RNTI MAC Control Element . 105
6.1.3.3 DRX Command MAC Control Element . 105
6.1.3.4 UE Contention Resolution Identity MAC Control Element . 106
6.1.3.5 Timing Advance Command MAC Control Element . 106
6.1.3.6 Power Headroom Report MAC Control Element . 106
6.1.3.6a Extended Power Headroom Report MAC Control Elements . 107
6.1.3.6b Dual Connectivity Power Headroom Report MAC Control Element . 110
6.1.3.7 MCH Scheduling Information MAC Control Element . 113
6.1.3.7a Extended MCH Scheduling Information MAC Control Element . 113
6.1.3.8 Activation/Deactivation MAC Control Elements . 114
6.1.3.9 Long DRX Command MAC Control Element . 115
6.1.3.10 Data Volume and Power Headroom Report MAC Control Element . 115
6.1.3.11 SPS confirmation MAC Control Element . 116
6.1.3.12 SC-PTM Stop Indication MAC Control Element . 116
6.1.3.13 Recommended bit rate MAC Control Element . 117
6.1.3.14 Activation/Deactivation of CSI-RS resources MAC Control Element . 118
6.1.3.15 Hibernation MAC Control Elements . 119
6.1.3.16 AUL confirmation MAC Control Element . 120
6.1.3.17 PDCP Duplication Activation/Deactivation MAC Control Element . 121
6.1.3.18 Downlink Channel Quality Report Command MAC Control Element . 121
6.1.3.19 Downlink Channel Quality Report and AS RAI MAC Control Element . 121
6.1.3.20 Timing Advance Report MAC Control Element. 122
6.1.3.21 Differential Koffset MAC Control Element . 122
6.1.3.22 GNSS Measurement Command MAC Control Element . 122
6.1.3.23 GNSS Validity Duration Report MAC Control Element . 123
6.1.3.24 UL Transmission Extension Update MAC Control Element . 123
6.1.4 MAC PDU (transparent MAC) . 123
6.1.5 MAC PDU (Random Access Response) . 124
6.1.6 MAC PDU (SL-SCH) . 126
6.1.7 MAC PDU (CB-Msg4) . 128
6.2 Formats and parameters . 130
6.2.1 MAC header for DL-SCH, UL-SCH and MCH. 130
6.2.2 MAC header for Random Access Response . 133
6.2.3 MAC payload for Random Access Response . 133
6.2.4 MAC header for SL-SCH . 133
6.2.5 MAC header for CB-Msg4 . 135
6.2.6 MAC payload for CB-Msg4 . 135
7 Variables and constants . 136
7.1 RNTI values . 136
7.2 Backoff Parameter values . 137
7.3 PRACH Mask Index values. 139
7.4 Subframe_Offset values . 139
7.5 TTI_BUNDLE_SIZE value. 140
7.6 DELTA_PREAMBLE values . 140
7.7 HARQ RTT Timers . 140
7.8 DL_REPETITION_NUMBER value . 143
7.9 UL_REPETITION_NUMBER value . 143
Annex A (normative): Handling of measurement gaps . 144
Annex B (normative): Contention resolution for RACH access . 145
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Annex C (informative): Intended UE behaviour for DRX Timers . 148
Annex D (normative): List of CRs Containing Early Implementable Features and Corrections . 150
Annex E (informative): Change history . 151
History . 160

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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.
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3GPP TS 36.321 version 19.2.0 Release 19 8 ETSI TS 136 321 V19.2.0 (2026-04)
1 Scope
The present document specifies the E-UTRA MAC protocol.
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 36.213: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer
Procedures".
[3] 3GPP TS 36.322: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control
(RLC) protocol specification".
[4] 3GPP TS 36.323: "Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data
Convergence Protocol (PDCP) Specification".
[5] 3GPP TS 36.212: "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and
channel coding".
[6] 3GPP TS 36.214: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer;
Measurements".
[7] 3GPP TS 36.211: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and
Modulation".
[8] 3GPP TS 36.331: "Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource
Control (RRC); Protocol specification".
[9] 3GPP TS 36.133: "Evolved Universal Terrestrial Radio Access (E-UTRA); Requirements for
support of radio resource management".
[10] 3GPP TS 36.101: "Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE)
radio transmission and reception".
[11] 3GPP TS 36.216: "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer for
relaying operation".
[12] 3GPP TS 36.306: "Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE)
radio access capabilities".
[13] 3GPP TS 23.303: "Proximity-based services (ProSe); Stage 2".
[14] 3GPP TS 23.285: "Architecture enhancements for V2X services".
[15] 3GPP TS 24.386: "User Equipment (UE) to V2X control function; protocol aspects; Stage 3".
[16] 3GPP TS 26.114: "IP Multimedia Subsystem (IMS); Multimedia telephony; Media handling and
interaction".
[17] 3GPP TS 38.323: "NR; Packet Data Convergence Protocol (PDCP) specification".
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[18] 3GPP TS 38.213: "NR; Physical Layer Procedures for control".
[19] 3GPP TS 38.133: "NR; Requirements for support of radio resource management".
[20] 3GPP TS 36.300: "Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal
Terrestrial Radio Access (E-UTRAN); Overall description; Stage 2".
[21] 3GPP TS 38.101-3: "NR; User Equipment (UE) radio transmission and reception; Part 3: Range 1
and Range 2 Interworking operation with other radios".
[22] 3GPP TS 38.306: "NR; User Equipment (UE) radio access capabilities".
[23] 3GPP TS 23.287: "Architecture enhancements for 5G System (5GS) to support Vehicle-to-
Everything (V2X) services ".
[24] 3GPP TS 38.321: "NR; Medium Access Control (MAC) protocol specification".
[25] 3GPP TS 38.331: "NR; Radio Resource Control (RRC); Protocol specification".
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].
Active Time: Time related to DRX operation, as defined in clause 5.7, during which the MAC entity monitors the
PDCCH.
CB-Msg3: Contention based message transmitted on UL-SCH as part of a CB-Msg3-EDT procedure.
CB-Msg3-EDT: A procedure which allows EDT from RRC_IDLE using contention based UL-SCH without random
access preamble transmission nor random access response reception.
CB-Msg3ResponseTimer: Specifies the number of consecutive subframe(s) during which the MAC entity shall monitor
the PDCCH after CB-Msg3(s) are transmitted.
CB-Msg4: The response message to one or more CB-Msg3s.
CB-RNTI: The contention based RNTI used on PDCCH when CB-Msg4s are transmitted.
DRX Cycle: Specifies the periodic repetition of the On Duration followed by a possible period of inactivity (see figure
3.1-1 below).
Figure 3.1-1: DRX Cycle
drx-InactivityTimer: Except for NB-IoT UEs, BL UEs or UEs in enhanced coverage, it specifies the number of
consecutive PDCCH-subframe(s) after the subframe in which a PDCCH indicates an initial UL, DL or SL user data
transmission for this MAC entity. For NB-IoT UEs, it specifies the number of consecutive PDCCH-subframe(s), after
the subframe in which the HARQ RTT timer or UL HARQ RTT timer expires, or after PDCCH indicates a new UL or
DL transmission for one TB when the UE is configured with multiple HARQ processes. For NB-IoT UEs in a non-
terrestrial network, it specifies the number of consecutive PDCCH-subframe(s) after the subframe as specified in clause
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5.7. For BL UEs or UEs in enhanced coverage, it specifies the number of consecutive PDCCH-subframe(s) following
the subframe containing the last repetition of the PDCCH reception that indicates an initial UL or DL user data
transmission for this MAC entity.
drx-RetransmissionTimer: Specifies the maximum number of consecutive PDCCH-subframe(s) until a DL
retransmission is received.
drx-RetransmissionTimerShortTTI: Specifies the maximum number of consecutive TTI(s) until a DL retransmission is
received for HARQ processes scheduled using short TTI.
drxShortCycleTimer: Specifies the number of consecutive subframe(s) the MAC entity shall follow the Short DRX
cycle.
drxStartOffset: Specifies the subframe where the DRX Cycle starts.
drx-ULRetransmissionTimer: Specifies the maximum number of consecutive PDCCH-subframe(s) until a grant for UL
retransmission or the HARQ feedback is received.
drx-ULRetransmissionTimeShortTTI: Specifies the maximum number of consecutive TTI(s) until a grant for UL
retransmission is received for HARQ processes scheduled using short TTI.
Early Data Transmission: Allows one uplink data transmission optionally followed by one downlink data transmission
during the random access procedure as specified in TS 36.300 [20]. The S1 connection is established or resumed upon
reception of the uplink data and may be released or suspended along with the transmission of the downlink data. Early
data transmission refers to both CP-EDT and UP-EDT.
HARQ information: HARQ information for DL-SCH or for UL-SCH transmissions consists of New Data Indicator
(NDI), Transport Block (TB) size. For DL-SCH transmissions and for asynchronous UL HARQ and for autonomous
UL HARQ, the HARQ information also includes HARQ process ID, except for UEs in NB-IoT configured with a single
HARQ process for which this information is not present. For UL-SCH transmission the HARQ information also
includes Redundancy Version (RV). In case of spatial multiplexing on DL-SCH the HARQ information comprises a set
of NDI and TB size for each transport block. HARQ information for SL-SCH and SL-DCH transmissions consists of
TB size only.
HARQ RTT Timer: This parameter specifies the minimum amount of subframe(s) before a DL assignment for HARQ
retransmission is expected by the MAC entity.
IoT NTN TDD: A mode of operation that allows use of NB-IoT FDD channels in TDD fashion, as defined in TS
36.300 [20].
mac-ContentionResolutionTimer: Specifies the number of consecutive subframe(s) during which the MAC entity shall
monitor the PDCCH after Msg3 is transmitted.
Msg3: Message transmitted on UL-SCH containing a C-RNTI MAC CE or a CCCH SDU optionally multiplexed with
DTCH for the UP-EDT, submitted from upper layer and associated with the UE Contention Resolution Identity, as part
of a random access procedure.
NB-IoT: NB-IoT allows access to network services via E-UTRA with a channel bandwidth limited to 200 kHz.
NB-IoT UE: A UE that uses NB-IoT.
NR sidelink communication: AS functionality enabling at least V2X Communication as defined in TS 23.287 [23],
between two or more nearby UEs, using NR technology but not traversing any network node.
Non-terrestrial networks: An E-UTRAN consisting of eNBs, which provide non-terrestrial LTE access to UEs by
means of an NTN payload embarked on a space-borne NTN vehicle and an NTN Gateway.
onDurationTimer: Specifies the number of consecutive PDCCH-subframe(s) at the beginning of a DRX Cycle.
PDCCH: Refers to the PDCCH (see TS 36.211 [7]), EPDCCH (in subframes when configured), MPDCCH (see TS
36.213 [2]), for an RN with R-PDCCH configured and not suspended, to the R-PDCCH, for NB-IoT to the NPDCCH or
for short TTI to SPDCCH.
PDCCH period (pp): Refers to the interval between the start of two consecutive PDCCH occasions and depends on the
currently used PDCCH search space, as specified in TS 36.213 [2]. A PDCCH occasion is the start of a search space
and is defined by subframe k0 as specified in clause 16.6 of TS 36.213 [2]. The calculation of number of PDCCH-
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subframes for the timer configured in units of a PDCCH period is done by multiplying the number of PDCCH periods
with npdcch-NumRepetitions-RA when the UE uses the common search space or by npdcch-NumRepetitions when the
UE uses the UE specific search space. When counting a timer whose length is calculated in PDCCH-subframes, the UE
shall include PDCCH-subframes that wi
...