Description
In 3GPP architecture, a Packet Data Network (PDN) is an external network that provides packet-switched data services to a User Equipment (UE). It is essentially an IP network that resides outside the 3GPP operator's domain. Common examples include the public Internet, an Internet Multimedia Subsystem (IMS) network for VoIP and VoLTE, or a private enterprise intranet. The primary function of the 3GPP core network—whether GPRS, EPS (4G), or 5GS (5G)—is to provide secure, policy-controlled connectivity between the UE and one or more PDNs.
The connection to a PDN is established through a Packet Data Protocol (PDP) Context in 3G/4G or a Protocol Data Unit (PDU) Session in 5G. This logical connection is anchored at a gateway node: the Gateway GPRS Support Node (GGSN) in 3G, the Packet Data Network Gateway (PDN-GW or PGW) in 4G EPS, and the User Plane Function (UPF) in 5G. This gateway acts as the point of entry and exit for all user plane traffic between the 3GPP network and the external PDN. It performs critical functions like IP address allocation to the UE (often from the PDN's address space), packet routing and forwarding, policy enforcement, charging, and traffic screening.
Each PDN is identified by an Access Point Name (APN), a textual label that the UE includes in its connection request. The APN is used by the network to determine the correct gateway and the specific external network to connect to. A single UE can have multiple simultaneous connections to different PDNs (e.g., one for internet, one for IMS), each with its own IP address and set of QoS characteristics. The PDN concept abstracts the details of the external network, allowing the 3GPP core to provide a consistent set of mobility, security, and policy functions regardless of whether the destination is the public internet or a specialized service network.
The role of the PDN has evolved with network generations. In 5G, the concept is generalized, but the principle remains. The 5G core network provides 'PDU Connectivity Services' to 'Data Networks' (DNs), which are the 5G equivalent of PDNs. The Service Continuity between EPS and 5GS relies heavily on maintaining PDN connectivity/PDU Sessions during inter-system handovers. The security boundary between the operator's trusted core and the external PDN is rigorously enforced at the gateway, using firewalling, Network Address Translation (NAT), and tunneling protocols like GTP or IPsec.
Purpose & Motivation
The concept of a Packet Data Network (PDN) was introduced to formalize and standardize how mobile networks provide access to external IP-based data services. In early cellular networks, data services were circuit-switched and limited. The shift to packet-switched data required a model where the mobile network acted as an access network to the broader internet and other IP networks. The PDN concept created a clear architectural separation between the operator's mobility management domain and the vast array of external service networks.
It solved the problem of how to route IP packets to and from a mobile subscriber whose point of attachment to the radio network changes constantly. The PDN Gateway (like GGSN/PGW) serves as a fixed anchor point in the IP topology, hiding the subscriber's mobility from the external PDN. This allows the UE to maintain a stable IP address and ongoing sessions even while moving across base stations. Without this anchor-and-tunnel model to a defined PDN, mobile IP data services would be impractical.
Historically, the PDN model enabled the commercial success of mobile internet. It provided the framework for billing (different rates for different PDNs via APNs), service differentiation (prioritizing IMS traffic over best-effort internet), and secure enterprise access (via private APNs). The evolution from 3G to 5G has seen the PDN concept become more flexible (supporting non-IP traffic in 5G) and integrated with network slicing, where a slice may provide dedicated connectivity to a specific type of PDN (e.g., an industrial IoT network). It remains a foundational abstraction for all mobile data services.
In the Network Map
- 4G EPC → PDN (External)
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (67 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, several enhancements were introduced for PDN connectivity procedures. These included the ability for a UE to attach without establishing a PDN connection, with support for Service Gap Control and allowing mobile-originated signalling in this state. The release also specified handling for non-IP type PDN connections using the default APN, introduced corrections for APN Rate Control during PDN connection release, and defined procedures for maintaining the UE's registered state without an active PDN connection.
- WLCP sublayer states for multiple bearer PDN connectivity TS 24.244CR0044
- Handling of PDN Connectivity Reject (cause #66) during an attach procedure TS 24.301CR3024
- Service Gap Control, attach without PDN connection for supporting UEs TS 24.301CR3036
- Correction on coding of PDN connection ID Information Element TS 24.244CR0056
- Keep PTI during UE initiated PDN disconnect procedure TS 24.301CR3008
- Service Gap control, attach without PDN connection and allow MO signalling TS 24.301CR3147
+ 6 more changes
In Release 16, enhancements for the PDN function included the introduction of Ethernet PDN connections in EPS and specific procedures for PDN connectivity status monitoring. It also defined the establishment of emergency PDN connections after WUS negotiation and clarified that no PDN connection is transferred during a 5G SRVCC handover procedure. Furthermore, it addressed procedures for PDN connectivity rejection with back-off timers and the support for PS data off for PDN connections established in N1 mode.
- PDN connectivity procedure for RLOS attached UEs TS 24.301CR3163
- Ethernet PDN connection TS 24.301CR3173
- PDU session ID usage when the UE is a 5G-RG and requests establishment of a PDN connection as a user-plane resource of a MA PDU session TS 24.301CR3326
- PDN connectivity status monitoring TS 29.122CR0087
- Feature applicability for PDN connectivity status TS 29.122CR0163
- PS data off for the PDN connection established in N1 mode TS 24.301CR3212
+ 7 more changes
In Release 17, enhancements to the PDN function focused on improving reliability, interworking, and session management. Key introductions included mechanisms for the restoration of PDN connections after gateway failures or changes, improved handling for interworking with 5GS, and support for local deactivation of user plane resources in multi-access sessions. The release also clarified procedures for emergency services and added capabilities like associating an S-NSSAI with a PDN connection after handover.
- PDN connections associated with the EPS bearer identities for which paging is restricted TS 24.301CR3548
- PDN connection release in case of standalone P-GW for interworking TS 24.301CR3580
- Considering PDN connection establishment rejected due to NSAC TS 24.301CR3601
- Local deactivation of UP resource for an MA PDU session with PDN leg - 24301 Part TS 24.301CR3657
- ECS address for PDN connection TS 24.301CR3685
- Restoration of PDN connections served by a combined SGW/PGW in a Set TS 29.274CR2029
+ 11 more changes
In Release 18, enhancements to the PDN function focused on supporting new service-specific connections and improving restoration and provisioning procedures. Key introductions included support for SDNAEPC capability indication during PDN connectivity, the inclusion of a DN-specific identity in the PDN CONNECTIVITY REQUEST message, and explicit procedures for USS UAV Authorization/Authentication during connection establishment. The release also provided significant clarifications and corrections for PDN connection restoration after a PGW-C/SMF change and for the handling of UE policy container provisioning.
- Indicating the capability of supporting SDNAEPC during the PDN connectivity procedure TS 24.301CR3851
- Rejecting PDN connectivity procedure due to SDNAEPC is not supported by the UE TS 24.301CR3852
- Include DN-specific identity in PDN CONNECTIVITY REQUEST TS 24.301CR3861
- Network slice admission control notification update for UE with atleast one PDU session/PDN connection TS 29.122CR0732
- Correction to condition to trigger TAU for local release of PDN connection TS 24.301CR3769
- Clarification of abnormal case in UE requested PDN connectivity procedure TS 24.301CR3888
+ 11 more changes
In Release 19, enhancements to the PDN function introduced procedures for PDN Connection Restoration Indication, including its inclusion during EPS to 5GS mobility. The release also specified new UE and network behaviors for emergency services, such as MME actions when a disaster condition ends and mechanisms for delayed Emergency PDN setup. Furthermore, it added capabilities for provisioning network slice information (S-NSSAI) via the PDN CONNECTIVITY REQUEST and for detecting duplicate PDN sessions with static IP allocation.
- Provisioning an S-NSSAI via the PDN CONNECTIVITY REQUEST message TS 24.301CR3655
- MME behaviour when the disaster condition has ended and the UE maintains a PDN connection for emergency bearer services TS 24.301CR4572
- PDN Connection Restoration Indication TS 29.274CR2111
- Including Pending PDN Connection Restoration Indication during EPS to 5GS mobility TS 29.274CR2112
- Delayed EMC PDN setup with pending SR TS 24.301CR4256
- Restricting access technology of E-UTRAN cell serving the UE without loss of PDN connections while the UE is in connected mode TS 24.301CR4297
+ 2 more changes
Explore further
Broader topics and technologies where PDN plays a role.
Defining Specifications
3GPP specifications that define or reference PDN, 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 23.110 vj00 | Access Stratum Services Specification | Rel-19 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TR 23.758 vh00 | Study on Edge Application Architecture | Rel-17 |
| TR 23.976 vj00 | Push Service Requirements Analysis | Rel-19 |
| TS 24.161 vj00 | Network-Based IP Flow Mobility (NBIFOM) | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.244 vj00 | Wireless LAN Control Plane Protocol | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.801 v810 | CT1 SAE NAS Aspects for EPC | Rel-8 |
| TR 26.938 vj00 | DASH Deployment Guidelines for 3GPP Networks | Rel-19 |
| TS 27.060 vj00 | TE-MT Interworking for Packet Domain | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.122 vj40 | T8 Reference Point for Northbound APIs | Rel-19 |
| TS 29.161 vc00 | 3GPP-WLAN Interworking Requirements | Rel-12 |
| TS 29.201 vj00 | RESTful Rx Interface for AF-PC Communication | Rel-19 |
| TS 29.273 vj10 | AAA Protocols for Non-3GPP Access in EPS & 5GS NSWO | Rel-19 |
| TS 29.274 vj50 | GTPv2-C Control Plane Protocol Specification | Rel-19 |
| TS 29.276 vj00 | EPS S101/S121/S103 Interfaces Stage 3 | Rel-19 |
| TS 29.279 vj00 | MIPv4 Mobility Protocol over S2a | Rel-19 |
| TS 29.817 vc10 | Study on XML-based Rx interface for PCC | Rel-12 |
| TS 31.111 vj30 | USIM Application Toolkit (USAT) Specification | Rel-19 |
| TS 31.829 vd00 | ISIM Conformance Requirements Technical Report | Rel-13 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | 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 |
| TS 32.295 vj00 | 3GPP Charging: CDR Transfer via GTP' Protocol | Rel-19 |
| TS 33.107 vj00 | Lawful Interception Architecture & Functions | Rel-19 |
| TS 33.108 vj00 | LI Handover Interface Specification | Rel-19 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 33.863 ve20 | Security for Battery-Efficient IoT Device to Enterprise | Rel-14 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
