Description
A Protocol Data Unit (PDU) is a standardized data block used for communication between peer entities within a layered protocol architecture, such as the OSI model or 3GPP protocol stacks. Each PDU is specific to a given layer (e.g., RRC, PDCP, RLC, MAC, NAS, GTP-U) and is composed of two main parts: the Protocol Control Information (PCI), which is the header added by the current layer containing instructions for the peer entity, and the Service Data Unit (SDU), which is the payload received from the layer above. For instance, an IP packet is the SDU for the PDCP layer, which adds its header to create a PDCP PDU. This PDU then becomes the SDU for the RLC layer, which in turn creates an RLC PDU, and so on down the stack.
In the 3GPP architecture, PDUs are central to every interface and procedure. On the radio interface (Uu), key PDUs include RRC PDUs for control signaling (e.g., RRCConnectionSetup), and user plane PDUs processed through the PDCP, RLC, and MAC layers. In the core network, NAS PDUs carry signaling between the UE and the AMF/SMF, while GTP-U PDUs tunnel user data between the gNB and UPF over the N3 interface. The processing of a PDU involves encapsulation at the transmitting side (adding headers/trailers) and decapsulation at the receiving side (stripping them off to retrieve the SDU for the higher layer). This layered processing ensures separation of concerns, modularity, and interoperability.
The role of the PDU is to provide a standardized container that ensures reliable, in-order, and secure delivery of information across the network. Different layers impart different characteristics to their PDUs. The RLC layer, for example, can segment or concatenate SDUs to fit radio resources, creating RLC PDUs. The MAC layer schedules MAC PDUs for transmission via transport blocks. In the core network, the PDU Session is a key concept representing an association for PDU connectivity service, where a PDU Session ID uniquely identifies the session, and user data flows as sequences of PDUs through established tunnels. Thus, the PDU is the atomic unit of data transfer that enables all 3GPP services, from voice calls to high-speed internet access.
Purpose & Motivation
The PDU concept exists to enable structured, layered communication in complex digital networks. Before standardized layered architectures, communication protocols were monolithic and inflexible, making them difficult to develop, debug, and evolve. The introduction of the PDU as part of layered models (like OSI and TCP/IP) solved the problem of managing complexity by dividing communication tasks into discrete layers, each with a specific function and a well-defined interface to adjacent layers. The PDU is the tangible object passed across these interfaces.
Historically, as telecommunications evolved from circuit-switched voice to packet-switched data, the need for a robust, multi-layered data unit became paramount. In 3GPP, starting from GSM and through UMTS, LTE, and now 5G, the PDU framework has provided consistency and backward compatibility. It addresses the limitation of having no common 'data currency' for different protocol functions. For example, the same IP packet (a network layer PDU) can be carried transparently through different radio access technologies (GERAN, UTRAN, E-UTRAN, NG-RAN) because each technology defines how to encapsulate it into its own link-layer PDUs (e.g., LLC PDUs, RLC PDUs).
Ultimately, the PDU is the foundational construct that allows for interoperability, efficient processing (e.g., header compression in PDCP), error correction (in RLC), and multiplexing (in MAC). It enables the network to treat different types of traffic (control vs. user plane) with appropriate reliability and priority. The evolution of PDU structures across releases (e.g., new PDCP headers for security, new RRC PDUs for 5G NR features) reflects the ongoing adaptation of the standards to new services and requirements, while maintaining the core principle of layered communication.
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (223 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, several key enhancements were introduced for the PDU Session function, including the new PDU Session type "IPv4v6" and support for Ethernet and Multi-homed IPv6 PDU Sessions. The release added the DNN as a configurable object in establishment parameters and defined procedures for SMF validation of UE location for LADN PDU Sessions. It also specified handling for non-3GPP access, SSC mode relations, and traffic routing influence for Ethernet-type sessions, while introducing mechanisms like the S-NSSAI back-off timer for session release.
- Addition of PDU Session type IPv4v6 TS 23.501CR0181
- Call Control update for PDU sessions TS 31.111CR0683
- Addition of DNN object in PDU session establishment parameters TS 31.111CR0705
- Configuration information the UE may exchange with the SMF during the lifetime of a PDU Session TS 23.501CR0003
- Relation between the SSC mode 3 and the PDU type TS 23.501CR0028
- UE support for Multi-homed IPv6 PDU Session TS 23.501CR0105
+ 42 more changes
In Release 16, key PDU session enhancements introduced Multi-Access (MA) PDU sessions, enabling simultaneous access over 3GPP and non-3GPP networks with features like ATSSS-LL support for Ethernet-type sessions and refined QoS handling for GBR flows. It also added capabilities for establishing redundant PDU sessions for URLLC traffic and clarified procedures for PDU session rate control, PCF selection, and interworking with EPS. Furthermore, the release provided specific corrections and clarifications for SMF and UPF selection, IP address accessibility, and N3/N9 tunnel management for these MA PDU sessions.
- QoS for Multi-Access PDU Session TS 23.501CR0770
- Clarification on MA PDU session TS 23.501CR1033
- Subscription Information Influence on PDU Session Rate Control TS 23.501CR1251
- Handling of Stored Small Data Rate Control Status at Subsequent PDU Session Establishment TS 23.501CR1252
- 23.501 part of PCF selection for PDU sessions with same DNN and S-NSSAI TS 23.501CR1375
- Interworking for MA PDU Session TS 23.501CR1571
+ 56 more changes
In Release 17, key enhancements for the PDU function included the introduction of Multi-Access (MA) PDU sessions with connectivity over E-UTRAN/EPC and non-3GPP access to the 5G Core, support for a restricted PDU Session for remote UE provisioning via the User Plane, and clarifications for handling Ethernet PDU Session types within MA sessions. The release also formalized support for Redundant PDU Sessions for URLLC, introduced the PDU Session Pair ID for use in URSP rules, and specified procedures for Emergency PDU session handling and transfer.
- MA PDU sessions with connectivity over E-UTRAN/EPC and non-3GPP access to 5GC TS 23.501CR2527
- Enabling restricted PDU Session for remote provisioning of UE via User Plane TS 23.501CR2709
- Clarification on UE provides PDU Session Pair ID based on URSP rules TS 23.501CR2736
- KI#3B, Resolving EN for Future PDU Session TS 23.501CR2791
- Support of RSN and PDU Session Pair ID in the URSP Rule TS 29.525CR0181
- PCF checking of redundant PDU session applicability TS 29.525CR0184
+ 14 more changes
In Release 18, key enhancements for the PDU function introduced the concept of a "PDU Set," enabling the handling of multiple related PDUs as a single group for QoS and uplink transmission management. The release also added support for graceful termination of PDU sessions during network slice decommissioning and optimized procedures for managing PDU Session Type changes and temporal validity conditions for groups of UEs. Furthermore, it improved Multi-Access PDU (MA-PDU) Session capabilities, including support for non-3GPP access connected to EPC and determining ATSSS capabilities when the UE supports MPQUIC.
- The support of Home Routed PDU Session supporting Session Breakout in VPLMN (HR-SBO) TS 23.501CR3830
- Change of Network Slice instance for PDU sessions TS 23.501CR3867
- Support non-3GPP access leg of MA-PDU Session with PDN connection in EPC TS 23.501CR3937
- KI#3, NEF exposure for handling PDU Session Type change and managing temporal invalidity/validity condition for a group of UEs TS 23.501CR3964
- Optimizations for the support of time vality policies for a network slice and graceful network slice PDU sessions release. TS 23.501CR4004
- Support of PDU Set based handling TS 23.501CR4046
+ 47 more changes
In Release 19, key enhancements for the PDU function included the introduction of PDU Set-based handling for both 3GPP and non-3GPP accesses, enabling more granular traffic management. This release specifically defined mechanisms for leveraging PDU Set QoS information for DSCP marking over the N3 and N9 transport interfaces and introduced support for identifying PDU Set information for encrypted traffic using protocols like MoQ and connect-UDP. Furthermore, it provided clarifications and new capabilities for Backhaul (BH) PDU Sessions, including NAT functionality in the UPF and support for an Alternative QoS profile with PDU Set QoS and Notification Control.
- Support PDU Set information identification based on MoQ for encrypted XRM traffic TS 23.501CR5632
- PDU Set Information Identification for end-to-end encrypted traffic using connect-UDP - architecture part TS 23.501CR5728
- MWAB BH PDU session clarification TS 23.501CR5828
- Leveraging PDU Set QoS information for DSCP marking over N3/N9 in the transport network TS 23.501CR5407
- PDU Set handling in non-3GPP accesses TS 23.501CR5608
- NAT functionality in the UPF of BH PDU Session TS 23.501CR5650
+ 31 more changes
In Release 20, the key new developments for the PDU function included the introduction of support for an Ethernet type of BH PDU Session for MWAB. Additionally, corrections were made to the Energy Consumption calculation methodology for scenarios involving redundant transmission or a PDU Session with multiple PDU Session Anchors. The release also addressed errors in the specifications for PDU Set based handling and PDU Set based QoS handling.
Explore further
Broader topics and technologies where PDU plays a role.
Defining Specifications
3GPP specifications that define or reference PDU, 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 22.060 vj00 | GPRS Stage 1 Service Description | Rel-19 |
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.107 vj00 | UMTS QoS Framework | Rel-19 |
| TS 23.140 v1600 | MMS Non-Realtime Service Definition | Rel-6 |
| TS 23.207 vj00 | End-to-End QoS Framework for GPRS | Rel-19 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.380 vj10 | IMS Restoration Procedures | Rel-19 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TR 23.745 vh00 | Study on App Layer Support for Factories of the Future in 5G | Rel-17 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TR 23.976 vj00 | Push Service Requirements Analysis | Rel-19 |
| TS 24.065 v1310 | GPRS Subnetwork Dependent Convergence Protocol | Rel-4 |
| TS 24.193 vj50 | ATSSS Procedures Specification | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.302 vj00 | Access to EPC via non-3GPP networks; Stage 3 | Rel-19 |
| TS 24.502 vj20 | 5G Core Access via Non-3GPP Networks; Stage 3 | Rel-19 |
| TS 25.221 vj00 | UTRA TDD Physical Layer Specification | Rel-19 |
| TS 25.301 vj00 | UE-UTRAN Radio Interface Protocol Architecture | Rel-19 |
| TS 25.302 vj00 | UTRA Physical Layer Services | Rel-19 |
| TS 25.321 vj00 | MAC Protocol Specification for UTRAN | Rel-19 |
| TS 25.322 vj00 | RLC Protocol Specification | Rel-19 |
| TS 25.323 vj00 | Packet Data Convergence Protocol (PDCP) Specification | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.402 vj00 | UTRAN Synchronisation Mechanisms | Rel-19 |
| TS 25.413 vj00 | Radio Access Network Application Part (RANAP) | Rel-19 |
| TS 25.414 vj00 | UTRAN Iu Interface User Plane Transport Protocols | Rel-19 |
| TS 25.415 vj00 | Iu Interface User Plane Protocol | Rel-19 |
| TS 25.419 vj00 | Service Area Broadcast Protocol (SABP) | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 25.427 vj00 | UTRAN Iub/Iur User Plane Protocols | Rel-19 |
| TS 25.468 vj00 | RANAP User Adaption (RUA) protocol specification | Rel-19 |
| TS 25.469 vj00 | HNBAP Specification for HNB to HNB-GW Interface | Rel-19 |
| TS 25.470 vj00 | PCAP User Adaption (PUA) protocol specification | Rel-19 |
| TS 25.471 vj00 | RNSAP User Adaptation (RNA) for Iurh | 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 26.110 vj00 | 3G-324M Multimedia Codecs for Circuit Switched Networks | Rel-19 |
| TS 26.143 vj00 | 5G Messaging Media Types and Codecs | Rel-19 |
| TS 26.501 vj30 | 5G Media Streaming (5GMS) Architecture | Rel-19 |
| TS 26.502 vj30 | 5G Multicast-Broadcast User Services Architecture | Rel-19 |
| TS 26.506 vj20 | Real-Time Media Communication Architecture for 5G | Rel-19 |
| TS 26.802 vj20 | Multicast Enhancements for 5G Media Streaming | Rel-19 |
| TR 26.803 vh00 | 5G Media Streaming Extensions for Edge Processing | Rel-17 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TR 26.806 vi00 | Technical Report on Smartly Tethering AR Glasses | Rel-18 |
| TS 26.854 vj00 | Study on Haptics in 5G Media Services | Rel-19 |
| TR 26.902 vj00 | Video Codec Performance for 3GPP Packet Services | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.928 vj00 | Study on eXtended Reality (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 |
| TR 26.941 vj01 | 5G Media Slicing Extensions | Rel-19 |
| TR 26.942 vj00 | Study on Media Energy Consumption Exposure & Evaluation | Rel-19 |
| TR 26.998 vj00 | 5G AR/MR Glasses Integration Study | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TS 28.062 vj00 | Tandem Free Operation (TFO) Service Description | Rel-19 |
| TS 28.203 vi10 | Charging management | Rel-18 |
| TS 28.204 vi11 | Charging management | Rel-18 |
| TR 28.833 vi01 | Technical Report on 5G LAN-type Service Management | Rel-18 |
| TR 28.840 vi10 | Technical Report | Rel-18 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.078 vj00 | CAMEL Phase 4 CAP Specification | Rel-19 |
| TS 29.171 vj00 | LCS Application Protocol (LCS-AP) Specification | Rel-19 |
| TS 29.274 vj50 | GTPv2-C Control Plane Protocol Specification | Rel-19 |
| TS 29.277 vj00 | S102 Interface Protocol Specification | Rel-19 |
| TS 29.278 vj00 | CAMEL Application Part (CAP) for IMS Phase 4 | Rel-19 |
| TS 29.281 vj20 | GTPv1-U Protocol Specification | Rel-19 |
| TS 29.414 vj00 | Nb Interface Bearer Transport & Control Protocols | Rel-19 |
| TS 29.415 vj00 | Nb User Plane Protocol Specification | Rel-19 |
| TS 29.525 vj40 | 5G UE Policy Control Service Stage 3 | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TR 32.847 vi00 | Technical Report | Rel-18 |
| TS 32.899 vf10 | 5G Charging Architecture Study | Rel-15 |
| TS 33.105 vj00 | 3G Security: Cryptographic Algorithm Requirements | Rel-19 |
| TR 33.739 vi10 | Study on security enhancement of support for | Rel-18 |
| TS 33.749 vj00 | Study on security aspects of edge computing enhancement | Rel-19 |
| TS 33.825 vg01 | Security for 5G URLLC Services | Rel-16 |
| TS 33.836 vg10 | Security Study for Advanced V2X Services | Rel-16 |
| TS 33.885 ve10 | Security Study for V2X Services | Rel-14 |
| 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 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 36.322 vj00 | E-UTRA Radio Link Control Protocol Specification | Rel-19 |
| TS 36.323 vj00 | PDCP Protocol Specification | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.355 vj00 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 36.360 vj00 | LTE-WLAN Aggregation Adaptation Protocol | Rel-19 |
| TS 36.361 vj00 | LWIP Encapsulation Protocol Specification | Rel-19 |
| TS 36.424 vj00 | X2 Interface User Plane Transport Protocols | Rel-19 |
| TS 36.938 v900 | E-UTRAN to 3GPP2/Mobile WiMAX Mobility | Rel-9 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.322 vj00 | NR Radio Link Control (RLC) Protocol | 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 38.424 vj00 | Xn Interface User Plane Transport Protocol | Rel-19 |
| TR 38.835 vi01 | Technical Report on XR Enhancements for NR | Rel-18 |
| TS 43.051 vj00 | GERAN Stage 2 Service Description | Rel-19 |
| TS 43.064 vj00 | GPRS Radio Interface Lower-Layer Functions | Rel-19 |
| TS 43.318 vj00 | Generic Access Network (GAN) Stage 2 | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TR 43.902 vj00 | GAN Enhancements Feasibility Study | Rel-19 |
| TS 44.060 vj00 | GERAN RLC/MAC Protocol Specification | Rel-19 |
| TS 44.065 vj00 | GPRS SNDCP Specification | Rel-19 |
| TS 44.160 vg00 | GERAN Iu Mode RLC/MAC Protocol Specification | Rel-16 |
| TS 44.318 vj00 | Generic Access Network (GAN) Interface Procedures | Rel-19 |
| TR 45.902 vj00 | Flexible Layer One (FLO) for GERAN | Rel-19 |
| TS 48.016 vj00 | Gb Interface Network Service Specification | Rel-19 |
