Description
The Packet Data Convergence Protocol (PDCP) is a crucial sublayer of the radio protocol stack in 3GPP access technologies, including UMTS (UTRAN), LTE (E-UTRAN), and NR (NG-RAN). It is defined for both the User Plane (UP) and Control Plane (CP). Architecturally, PDCP entities are located in the User Equipment (UE) and in the network node (NodeB/eNodeB/gNB), one per Radio Bearer. Its primary functions are convergence, meaning it adapts higher-layer protocols (typically IP) for efficient transmission over the specific radio interface.
For the User Plane, PDCP performs Robust Header Compression (ROHC) to significantly reduce the size of IP packet headers (e.g., IPv4, IPv6, UDP, RTP), which are large relative to payload for many applications, thereby saving precious air interface bandwidth. It also provides security through ciphering (encryption) of the user data payload to ensure confidentiality. Furthermore, for LTE and NR, PDCP ensures in-sequence delivery and duplicate detection of data packets during handover procedures. It manages the PDCP Sequence Number (SN) and buffers packets to allow lossless handover when the underlying RLC layer is operating in Acknowledged Mode (AM).
For the Control Plane, specifically for RRC and NAS messages, PDCP provides integrity protection and ciphering. Integrity protection guarantees that control messages have not been tampered with during transmission. PDCP performs these security functions using keys derived by the NAS and AS security procedures. The protocol operates by receiving Service Data Units (SDUs) from the higher layers (IP or RRC), attaching a PDCP header containing the sequence number, performing the configured operations (compression, ciphering), and then passing the resulting Protocol Data Unit (PDU) to the RLC layer below. During reception, the process is reversed. Its role is fundamental to achieving efficient, secure, and reliable data delivery in modern cellular networks.
Purpose & Motivation
PDCP was introduced to address the inefficiencies and security shortcomings of transmitting Internet Protocol (IP) packets directly over the radio link in 3G UMTS. In early 3G releases, the protocol stack lacked a dedicated convergence layer, making IP packet transmission over the air resource-intensive due to large, repetitive headers. This was particularly problematic for voice-over-IP (VoIP) and interactive gaming where small payloads are dwarfed by IP/UDP/RTP headers.
The protocol solves several key problems. First, header compression (initially introduced in Rel-4) dramatically improves spectral efficiency and reduces latency for IP-based services. Second, it centralizes ciphering for user data at a layer above RLC, simplifying security architecture and enabling ciphering even when RLC is in Transparent Mode. Third, with the move to a flatter, all-IP architecture in LTE, PDCP's role expanded to include in-order delivery and duplicate removal, which are essential for maintaining data integrity during handovers between eNodeBs, especially for delay-sensitive services. Its creation was motivated by the need to optimize the radio interface for the explosive growth of IP traffic, ensure robust security, and support seamless mobility in increasingly heterogeneous network environments.
Protocol Stack
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (79 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the PDCP function introduced the PDCP duplication feature for increased reliability, along with specific support for this feature over the X2 interface and for CA-based duplication. The release also added a PDCP suspend procedure, clarified the PDCP structure for split and LWA bearers, and introduced new capabilities like notifying and modifying the PDCP SN length.
- Introduction of PDCP duplication TS 38.323CR0009
- Inclusion of Maximum Number of PDCP SDUs per TTI for DL Categories 22-26 TS 36.306CR1736
- Deliver stored PDCP SDUs for UM DRB at PDCP re-establishment TS 36.323CR0241
- CR on supporting of the ROHC for PDCP duplication TS 36.323CR0243
- Correction on PDCP for eV2X TS 36.323CR0249
- Correction on PDCP duplication TS 36.323CR0255
+ 29 more changes
In Release 16, key PDCP enhancements included the introduction of Ethernet Header Compression (EHC) for LTE, enabling a PDCP version change without requiring a handover procedure. The release also introduced corrections and clarifications for PDCP operation in IIoT scenarios, for duplication functionality, and for re-establishment procedures, particularly when using t-Reordering or for suspended AM DRBs. Furthermore, it addressed security in duplicate detection, queuing delay measurements, and the behavior upon RRC resume or re-establishment.
- Introducing EHC in LTE PDCP TS 36.323CR0278
- Allowing PDCP version change without handover TS 36.306CR1754
- LTE PDCP corrections for NR IIOT TS 36.323CR0286
- Correction for PDCP status report TS 36.323CR0287
- CR on LTE PDCP re-establishment when t-Reordering is used TS 36.323CR0290
- CR on LTE PDCP re-establishment for UM DRB when t-Reordering is used TS 36.323CR0291
+ 13 more changes
In Release 17, the primary new feature for PDCP was the introduction of support for User Plane IP (UP IP) in EPC-connected architectures using NR PDCP. This enhancement was accompanied by various corrections and clarifications across several areas, including SL relay, L2 U2N Relay, Multicast/Broadcast Service (MBS), and PDCP Control PDUs for UDC feedback. Other updates addressed procedural aspects for sidelink radio bearers and entity establishment.
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 36.300CR1353
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 36.331CR4763
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.323CR0085
- Introducing support of UP IP for EPC connected architectures using NR PDCP TS 38.331CR2904
- Correction on PDCP Control PDU for UDC feedback TS 36.323CR0304
- Stage-2 correction on the UL PDCP packet average delay TS 37.320CR0126
+ 10 more changes
In Release 18, the PDCP function introduced support for NR sidelink PDCP duplication and a new PDCP Sequence Number gap reporting procedure. The release also included corrections and clarifications for the Delay Critical Indication from PDCP to RLC, the configuration of PDCP duplication for split SRB in NR-DC, and the PDCP configuration for multicast MRB.
- Introduction of NR sidelink PDCP duplication in TS 38.323 TS 38.323CR0126
- PDCP SN gap reporting TS 38.323CR0139
- Correction for Delay Critical Indication from PDCP to RLC TS 38.323CR0144
- PDCP SN Gap report Corrections TS 38.323CR0147
- Correction on pdcp-DuplicationSRB for NR-DC TS 38.306CR1303
- Correction to PDCP configuration for multicast MRB TS 38.331CR4651
In Release 19, the primary enhancements for PDCP focused on supporting Extended Reality (XR) traffic. The changes introduced specific XR-related enhancements to the PDCP specification and included subsequent corrections to these new features. Additionally, corrections were made to the PDCP configuration parameters for Signaling Radio Bearers 4 and 5 (SRB4 and SRB5).
Explore further
Broader topics and technologies where PDCP plays a role.
Defining Specifications
3GPP specifications that define or reference PDCP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 23.725 vg20 | Study on URLLC Architecture Enhancements | Rel-16 |
| TS 25.301 vj00 | UE-UTRAN Radio Interface Protocol Architecture | Rel-19 |
| TS 25.323 vj00 | Packet Data Convergence Protocol (PDCP) Specification | Rel-19 |
| TS 25.324 vj00 | Broadcast/Multicast Control Protocol | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TR 25.912 vj00 | Evolved UTRA and UTRAN Technical Report | Rel-19 |
| TR 25.931 vj00 | UTRAN Signalling Procedures Examples | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.935 vj00 | Speech Codec Performance for Packet Switched Multimedia | Rel-19 |
| TR 26.937 vj00 | 3GPP PSS Characterization | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TR 28.837 vi00 | Technical Report on Trace/MDT Management | Rel-18 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 33.401 vj10 | EPS Security Architecture | Rel-19 |
| TS 33.821 v900 | LTE/SAE Security Threat Analysis and Countermeasures | Rel-9 |
| TS 33.825 vg01 | Security for 5G URLLC Services | Rel-16 |
| TS 33.835 vg10 | Study on authentication and key management for apps | Rel-16 |
| TS 33.836 vg10 | Security Study for Advanced V2X Services | Rel-16 |
| TS 33.843 vf10 | Security Study for ProSe UE-to-Network Relay | Rel-15 |
| TR 33.938 vj10 | 3GPP Cryptographic Inventory for 5G | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.302 vj00 | E-UTRA Physical Layer Services | Rel-19 |
| TS 36.306 vj00 | E-UTRA UE Radio Access Capability Parameters | Rel-19 |
| TS 36.323 vj00 | PDCP Protocol Specification | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.360 vj00 | LTE-WLAN Aggregation Adaptation Protocol | Rel-19 |
| TS 36.361 vj00 | LWIP Encapsulation Protocol Specification | Rel-19 |
| TS 36.413 vj10 | S1 Application Protocol (S1AP) | Rel-19 |
| TS 36.423 vj10 | X2 Application Protocol (X2AP) Specification | Rel-19 |
| TS 36.424 vj00 | X2 Interface User Plane Transport Protocols | Rel-19 |
| TS 36.463 vj00 | XwAP Protocol Specification | Rel-19 |
| TS 36.938 v900 | E-UTRAN to 3GPP2/Mobile WiMAX Mobility | Rel-9 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TS 38.306 vj00 | NR UE Radio Access Capability Parameters | Rel-19 |
| TS 38.323 vj00 | Packet Data Convergence Protocol (PDCP) | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.415 vj10 | PDU Session User Plane Protocol | Rel-19 |
| TS 38.424 vj00 | Xn Interface User Plane Transport Protocol | Rel-19 |
| TS 43.051 vj00 | GERAN Stage 2 Service Description | Rel-19 |
| TS 44.060 vj00 | GERAN RLC/MAC Protocol Specification | Rel-19 |
| TS 44.160 vg00 | GERAN Iu Mode RLC/MAC Protocol Specification | Rel-16 |
