ETSI TS 138 323 V18.5.0 (2025-04)

5G; NR; Packet Data Convergence Protocol (PDCP) specification (3GPP TS 38.323 version 18.5.0 Release 18)

RTS/TSGR-0238323vi50

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: 03-Apr-2025

Standards Content (Sample)

TECHNICAL SPECIFICATION
5G;
NR;
Packet Data Convergence Protocol (PDCP) specification
(3GPP TS 38.323 version 18.5.0 Release 18)

3GPP TS 38.323 version 18.5.0 Release 18 1 ETSI TS 138 323 V18.5.0 (2025-04)

Reference
RTS/TSGR-0238323vi50
Keywords
5G
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ETSI
3GPP TS 38.323 version 18.5.0 Release 18 2 ETSI TS 138 323 V18.5.0 (2025-04)
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ETSI
3GPP TS 38.323 version 18.5.0 Release 18 3 ETSI TS 138 323 V18.5.0 (2025-04)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 7
2 References . 7
3 Definitions and abbreviations . 8
3.1 Definitions . 8
3.2 Abbreviations . 9
4 General . 10
4.1 Introduction . 10
4.2 Architecture . 10
4.2.1 PDCP structure . 10
4.2.2 PDCP entities . 13
4.3 Services . 14
4.3.1 Services provided to upper layers . 14
4.3.2 Services expected from lower layers . 14
4.4 Functions . 15
5 Procedures . 15
5.1 PDCP entity handling . 15
5.1.1 PDCP entity establishment . 15
5.1.2 PDCP entity re-establishment . 15
5.1.3 PDCP entity release . 17
5.1.4 PDCP entity suspend . 17
5.1.5 PDCP entity reconfiguration . 18
5.2 Data transfer . 18
5.2.1 Transmit operation . 18
5.2.2 Receive operation . 20
5.2.2.1 Actions when a PDCP Data PDU is received from lower layers . 20
5.2.2.2 Actions when a t-Reordering expires . 22
5.2.2.3 Actions when the value of t-Reordering is reconfigured . 22
5.2.3 Sidelink transmit operation . 22
5.2.4 Sidelink receive operation . 22
5.3 SDU discard . 23
5.4 Status reporting . 23
5.4.1 Transmit operation . 23
5.4.2 Receive operation . 24
5.5 Data recovery . 24
5.6 Data volume calculation . 24
5.7 Robust header compression and decompression . 26
5.7.1 Supported header compression protocols and profiles . 26
5.7.2 Configuration of ROHC . 26
5.7.3 Protocol parameters . 26
5.7.4 Header compression using ROHC . 27
5.7.5 Header decompression using ROHC . 27
5.7.6 PDCP Control PDU for interspersed ROHC feedback . 27
5.7.6.1 Transmit Operation . 27
5.7.6.2 Receive Operation . 28
5.8 Ciphering and deciphering . 28
5.9 Integrity protection and verification . 28
5.10 Handling of unknown, unforeseen, and erroneous protocol data . 29
5.11 PDCP duplication . 30
5.11.1 Activation/Deactivation of PDCP duplication . 30
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5.11.2 Duplicate PDU discard . 30
5.12 Ethernet header compression and decompression . 31
5.12.1 Supported header compression protocols . 31
5.12.2 Configuration of EHC . 31
5.12.3 Protocol parameters . 31
5.12.4 Header compression using EHC . 31
5.12.5 Header decompression using EHC . 31
5.12.6 PDCP Control PDU for EHC feedback . 31
5.12.6.1 Transmit Operation . 31
5.12.6.2 Receive Operation . 31
5.12.7 Simultaneous configuration of ROHC and EHC . 32
5.13 Uplink data switching . 32
5.14 Uplink Data compression and decompression . 33
5.14.1 UDC protocol. 33
5.14.2 Configuration of UDC . 33
5.14.3 UDC header . 33
5.14.4 Uplink data compression . 33
5.14.5 PDCP Control PDU for UDC feedback . 33
5.14.6 Pre-defined dictionary . 34
5.14.7 UDC buffer reset procedure . 34
5.14.8 UDC checksum error handling . 34
5.15 Data volume calculation for delay status reporting . 34
5.16 SN gap report . 35
5.16.1 Transmit operation . 35
5.16.2 Receive operation . 35
6 Protocol data units, formats, and parameters . 36
6.1 Protocol data units . 36
6.1.1 Data PDU . 36
6.1.2 Control PDU . 36
6.2 Formats . 37
6.2.1 General . 37
6.2.2 Data PDU . 37
6.2.2.1 Data PDU for SRBs . 37
6.2.2.2 Data PDU for DRBs and MRBs with 12 bits PDCP SN . 37
6.2.2.3 Data PDU for DRBs and MRBs with 18 bits PDCP SN . 38
6.2.2.4 Data PDU for sidelink DRBs for groupcast and broadcast, for the sidelink SRB0 and for the
sidelink SRB4 . 38
6.2.2.5 Data PDU for sidelink SRBs for unicast . 39
6.2.2.6 Data PDU for sidelink DRBs for unicast with 12 bits PDCP SN . 39
6.2.2.7 Data PDU for sidelink DRBs for unicast with 18 bits PDCP SN . 40
6.2.3 Control PDU . 41
6.2.3.1 Control PDU for PDCP status report . 41
6.2.3.2 Control PDU for interspersed ROHC feedback . 42
6.2.3.3 Control PDU for EHC feedback. 42
6.2.3.4 Control PDU for UDC feedback . 42
6.2.3.5 Control PDU for PDCP SN gap report . 42
6.3 Parameters . 43
6.3.1 General . 43
6.3.2 PDCP SN . 43
6.3.3 Data . 43
6.3.4 MAC-I . 44
6.3.5 COUNT . 44
6.3.6 R . 44
6.3.7 D/C. 44
6.3.8 PDU type . 44
6.3.9 FMC . 45
6.3.10 Bitmap . 45
6.3.11 Interspersed ROHC feedback . 45
6.3.12 SDU Type . 45
6.3.13 K ID . 45
NRP-sess
6.3.14 FE. 46
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6.3.15 FDC . 46
6.3.16 Discard Bitmap . 46
7 State variables, constants, and timers . 46
7.1 State variables . 46
7.2 Constants . 47
7.3 Timers . 47
Annex A (normative): Ethernet Header Compression (EHC) protocol . 49
A.1 EHC principle . 49
A.2 EHC packet format and parameters . 50
A.2.1 EHC packet format . 50
A.2.1.1 EHC Full Header packet and EHC Compressed Header packet . 50
A.2.1.2 EHC feedback packet. 51
A.2.2 Parameters . 52
A.2.2.1 F/C . 52
A.2.2.2 CID . 52
Annex B (normative): Uplink Data Compression Protocol . 53
B.1 UDC general description . 53
B.2 UDC packet format and parameters . 53
B.2.1 UDC Header and UDC Data Block format . 53
B.2.2 UDC parameters . 53
B.2.2.1 FU . 53
B.2.2.2 FR . 53
B.2.2.3 Checksum . 54
B.2.3 An example of UDC Checksum calculation . 54
Annex C (informative): Change history . 55
History . 58

ETSI
3GPP TS 38.323 version 18.5.0 Release 18 6 ETSI TS 138 323 V18.5.0 (2025-04)
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
3GPP TS 38.323 version 18.5.0 Release 18 7 ETSI TS 138 323 V18.5.0 (2025-04)
1 Scope
The present document provides the description of the Packet Data Convergence Protocol (PDCP).

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: "NG Radio Access Network; Overall description".
[3] 3GPP TS 38.331: "NR Radio Resource Control (RRC); Protocol Specification".
[4] 3GPP TS 38.321: "NR Medium Access Control (MAC) protocol specification".
[5] 3GPP TS 38.322: "NR Radio Link Control (RLC) protocol specification".
[6] 3GPP TS 33.501: "Security Architecture and Procedures for 5G System ".
[7] IETF RFC 5795: "The RObust Header Compression (ROHC) Framework".
[8] IETF RFC 3095: "RObust Header Compression (ROHC): Framework and four profiles: RTP,
UDP, ESP and uncompressed".
[9] IETF RFC 4815: "RObust Header Compression (ROHC): Corrections and Clarifications to RFC
3095".
[10] IETF RFC 6846: "RObust Header Compression (ROHC): A Profile for TCP/IP (ROHC-TCP)".
[11] IETF RFC 5225: "RObust Header Compression (ROHC) Version 2: Profiles for RTP, UDP, IP,
ESP and UDP Lite".
[12] 3GPP TS 36.321: "Evolved Universal Terrestrial Radio Access (E-UTRA) Medium Access
Control (MAC) protocol specification".
[13] 3GPP TS 23.287: "Architecture enhancements for 5G System (5GS) to support Vehicle-to-
Everything (V2X) services".
[14] 3GPP TS 33.536: "Security Aspect of 3GPP Support for Advanced V2X Services".
[15] IEEE Standard 802.3™-2018: "Ethernet".
[16] 3GPP TS 24.587: "Vehicle-to-Everything (V2X) services in 5G System (5GS), Stage 3".
[17] 3GPP TS 33.401: "3GPP System Architecture Evolution (SAE); Security Architecture".
[18] 3GPP TS 23.304: "Proximity based Services (ProSe) in the 5G System (5GS)".
[19] IETF RFC 1951: "DEFLATE Compressed Data Format Specification version 1.3".
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3GPP TS 38.323 version 18.5.0 Release 18 8 ETSI TS 138 323 V18.5.0 (2025-04)
[20] IETF RFC 3485: "The Session Initiation Protocol (SIP) and Session Description Protocol (SDP)
Static Dictionary for Signaling Compression (SigComp)".
[21] IETF RFC 1979: "PPP Deflate Protocol".
[22] 3GPP TS 38.351: "NR; Sidelink Relay Adaptation Protocol (SRAP) Specification".
[23] 3GPP TS 23.501: "System Architecture for the 5G System; Stage 2".
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].
AM DRB: a data radio bearer which utilizes RLC AM.
AM MRB: an MRB associated with at least one AM RLC bearer for PTP transmission.
Broadcast MRB: a radio bearer configured for MBS broadcast delivery.
DAPS bearer: a bearer whose radio protocols are located in both the source gNB and the target gNB during DAPS
handover to use both source gNB and target gNB resources.
Delay-critical PDCP SDU: if pdu-SetDiscard is not configured, a PDCP SDU for which the remaining time till
discardTimer expiry is less than the remainingTimeThreshold. If pdu-SetDiscard is configured, a PDCP SDU belonging
to a PDU Set of which at least one PDCP SDU has the remaining time till discardTimer expiry less than the
remainingTimeThreshold.
MBS Radio Bearer: a radio bearer that is configured for MBS delivery.
Multicast MRB: a radio bearer configured for MBS multicast delivery.
Multi-path: Mode of operation of a remote UE in RRC_CONNECTED configured with one direct path on which the
UE connects to the gNB using NR Uu and one indirect path on which the UE connects to the same gNB via another UE
using PC5 unicast link or Non-3GPP Connection.
Multi-path Primary Path: In multi-path for a split DRB, the primary path is configured by RRC to be either the direct
path or the indirect path. In multi-path for a split SRB, the primary path is always the direct path.
Multi-path Secondary Path: In multi-path for a split DRB, the path (either direct or indirect) which is not configured
by RRC as the primary path. In multi-path for a split SRB, the secondary path is always the indirect path (SL or N3C).
Multi-path split bearer: In multi-path, a bearer in which one PDCP entity is mapped to one or more (direct) Uu RLC
entities and either one SRAP entity of a SL indirect path or a non-3GPP connection.
N3C indirect path: In multi-path, the indirect path using Non-3GPP Connection between remote UE and relay UE.
Non-split bearer: a bearer whose radio protocols are located in either the MgNB or the SgNB to use MgNB or SgNB
resource, respectively.
NR sidelink communication: AS functionality enabling at least V2X communication as defined in TS 23.287 [13] and
ProSe communication (including ProSe non-Relay, UE-to-Network Relay, and UE-to-UE Relay communication) as
defined in TS 23.304 [18], between two or more nearby UEs, using NR technology but not traversing any network
node.
NR sidelink discovery: AS functionality enabling ProSe non-Relay Discovery, ProSe UE-to-Network Relay discovery,
and ProSe UE-to-UE Relay discovery for Proximity based Services as defined in TS 23.304 [18] between two or more
nearby UEs, using NR technology but not traversing any network node.
NR sidelink transmission: any NR Sidelink-based transmission, including both transmission for NR sidelink discovery
and transmission for NR sidelink communication.
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PDCP data volume: the amount of data available for transmission in a PDCP entity.
PDU Set: one or more PDUs carrying the payload of one unit of information generated at the application level (e.g.
frame(s) or video slice(s) etc. for XR services), as defined in TS 23.501 [23]. A PDU in the PDU Set corresponds to a
PDCP SDU.
SL indirect path: In multi-path, the indirect path on which the L2 U2N Remote UE connects to the network via a L2
U2N Relay UE.
Split bearer: in dual connectivity, a bearer whose radio protocols are located in both the MgNB and the SgNB to use
both MgNB and SgNB resources.
Split secondary RLC entity: in dual connectivity, the RLC entity other than the primary RLC entity which is
responsible for split bearer operation. If the PDCP entity is associated with two RLC entities, the split secondary RLC
entity is the RLC entity other than the primary RLC entity. If the PDCP entity is associated with more than two RLC
entities, the split secondary RLC entity is configured by upper layers. In multi-path, the split secondary RLC entity is
the RLC entity on the direct path which is responsible for split bearer operation when the MP primary path is the
indirect path. When the PDCP entity on the direct path is associated with one RLC entity, the split secondary RLC
entity is that RLC entity. When the PDCP entity is associated with more than one RLC entity, the split secondary RLC
entity is configured by upper layers.
UM DRB: a data radio bearer which utilizes RLC UM.
UM MRB: an MRB associated with only RLC UM.
U2N Relay UE: A UE that provides functionality to support connectivity to the network for U2N Remote UE(s).
U2N Remote UE: A UE that communicates with the network via a U2N Relay UE.
U2U Relay UE: A UE that provides functionality to support connectivity between two U2U Remote UEs
U2U Remote UE: A UE that communicates with another UE via a U2U Relay UE
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
ARP Address Resolution Protocol
CID Context Identifier
DAPS Dual Active Protocol Stack
DRB Data Radio Bearer carrying user plane data
EHC Ethernet Header Compression
FIFO First In First Out
gNB NR Node B
HFN Hyper Frame Number
IETF Internet Engineering Task Force
IP Internet Protocol
MAC Medium Access Control
MAC-I Message Authentication Code for Integrity
MBS Multicast/Broadcast Services
MP Multi-path
MRB MBS Radio Bearer
MTCH MBS Traffic Channel
N3C Non-3GPP Connection
PDCP Packet Data Convergence Protocol
PDU Protocol Data Unit
PSI PDU Set Importance
RB Radio Bearer
RFC Request For Comments
RLC Radio Link Control
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ROHC RObust Header Compression
RRC Radio Resource Control
RTP Real Time Protocol
SAP Service Access Point
SCCH Sidelink Control Channel
SDU Service Data Unit
SLRB Sidelink Radio Bearer carrying NR sidelink communication or NR sidelink discovery
SN Sequence Number
SRAP Sidelink Relay Adaptation Protocol
SRB Signalling Radio Bearer carrying control plane data
STCH Sidelink Traffic Channel
TCP Transmission Control Protocol
UDC Uplink Data Compression
UDP User Datagram Protocol
UE User Equipment
UM Unacknowledged Mode
U2N UE-to-Network
X-MAC Computed MAC-I
4 General
4.1 Introduction
The present document describes the functionality of the PDCP.
4.2 Architecture
4.2.1 PDCP structure
Figure 4.2.1-1 represents one possible structure for the PDCP sublayer for non-relay scenario. Figure 4.2.1-2 represents
one possible structure for the PDCP sublayer used in L2 U2N relay case, L2 U2U relay case, and for the indirect path in
the case of multi-path with SL indirect path. Figure 4.2.1-3 represents one possible structure for the PDCP sublayer
used for the indirect path in the case of multi-path with N3C indirect path. These structures should not restrict
implementation. The figures are based on the radio interface protocol architecture defined in TS 38.300 [2].
NOTE: The structure and interface of non-3GPP connection for the case of multi-path with N3C indirect path is
out of the scope of this specification.
ETSI
3GPP TS 38.323 version 18.5.0 Release 18 11 ETSI TS 138 323 V18.5.0 (2025-04)

Figure 4.2.1-1: PDCP layer, structure view (normal)

Figure 4.2.1-2: PDCP layer, structure view (L2 U2N relay), L2 U2U relay and SL indirect path in multi-
path
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Remote UE
Radio Bearers
PDCP-SAP
PDCP-SAP
... PDCP
C-SAP
sublayer
PDCP entity PDCP entity
PDCP - PDU
Non-3GPP-SAP
Non-3GPP connection
Figure 4.2.1-3: PDCP layer, structure view (N3C indirect path in multi-path)
The PDCP sublayer is configured by upper layers TS 38.331 [3]. The PDCP sublayer is used for RBs mapped on
DCCH, DTCH, MTCH, SCCH, and STCH type of logical channels. The PDCP sublayer is not used for any other type
of logical channels.
Each RB (except for SRB0 for Uu interface) is associated with one PDCP entity. Each PDCP entity is associated with
one, two, three, four, six, or eight RLC entities depending on the RB characteristic (e.g. uni-directional/bi-directional or
split/non-split) or RLC mode:
- For split bearers, each PDCP entity is associated with two UM RLC entities (for same direction), four UM RLC
entities (two for each direction), or two AM RLC entities;
- For RBs configured with PDCP duplication, each PDCP entity is associated with N UM RLC entities (for same
direction), 2 × N UM RLC entities (N for each direction), or N AM RLC entities, where 2 <= N <= 4;
- For DAPS bearers, each PDCP entity is associated with two UM RLC entities (for same direction, one for source
and one for target cell), four UM RLC entities (two for each direction on source cell and target cell), or two AM
RLC entities (one for source cell and one for target cell);
- For UM MRBs, each PDCP entity is associated with one UM RLC entity (for MTCH or for downlink DTCH),
two UM RLC entities (one for MTCH and one for downlink DTCH, or one for downlink DTCH and one for
uplink DTCH), or three UM RLC entities (one for MTCH, one for downlink DTCH, and one for uplink DTCH);
- For AM MRBs, each PDCP entity is associated with one AM RLC entity (for downlink DTCH and uplink
DTCH), or one UM RLC entity (for MTCH) and one AM RLC entity (for downlink DTCH and uplink DTCH);
- For MP split bearers with SL indirect path, each PDCP entity is associated with one or more Uu RLC entities
and one SRAP entity;
- For MP split bearers with N3C indirect path, each PDCP entity is associated with one or more Uu RLC entities
and the N3C;
- Otherwise, each PDCP entity is associated with one UM RLC entity, two UM RLC entities (one for each
direction), or one AM RLC entity.
For the case of L2 U2N relay, L2 U2U relay and SL indirect path of multi-path, all PDCP entities are associated with
one SRAP entity. For the case of N3C indirect path for multi-path, all PDCP entities of the MP remote UE are
associated with the N3C.
ETSI
Packets not
associated to a
PDCP SDU
Packets not
associated to a
PDCP SDU
3GPP TS 38.323 version 18.5.0 Release 18 13 ETSI TS 138 323 V18.5.0 (2025-04)
4.2.2 PDCP entities
The PDCP entities are located in the PDCP sublayer. Several PDCP entities may be defined for a UE. Each PDCP
entity is carrying the data of one radio bearer. A PDCP entity is associated either to the control plane or the user plane
depending on which radio bearer it is carrying data for.
Figure 4.2.2-1 represents the functional view of the PDCP entity for the PDCP sublayer; it should not restrict
implementation. The figure is based on the radio interface protocol architecture defined in TS 38.300 [2].
For split bearers, MP split bearers, and DAPS bearers, routing is performed in the transmitting PDCP entity.
A PDCP entity associated with DRB can be configured by upper layers TS 38.331 [3] to use header compression or
uplink data compression (UDC). A PDCP entity associated with MRB can be configured by upper layers TS 38.331 [3]
to use header compression. In this version of the specification, the robust header compression protocol (ROHC), the
Ethernet header compression protocol (EHC) and UDC are supported. Each header compression protocol is
independently configured for a DRB/MRB.
UE/NG-RAN/UE A NG-RAN/UE/UE B
Transmitting Receiving
P
...