Description
The PDN Gateway (PGW) is a central node in the 3GPP Evolved Packet Core (EPC) architecture, introduced with LTE in Release 8. It resides at the boundary between the mobile operator's trusted network and external Packet Data Networks (PDNs), such as the public internet, an IMS network, or a corporate intranet. For each User Equipment (UE), at least one PGW is assigned to handle its data sessions, known as PDN connections. The PGW establishes a GTP (GPRS Tunnelling Protocol) tunnel with the Serving Gateway (SGW) for user plane traffic and interacts with control plane entities like the MME and PCRF.
Architecturally, the PGW performs several vital roles. It is the point of IP address allocation for the UE, typically using DHCP or acting as a DHCP server. It enforces policy and charging control rules received from the Policy and Charging Rules Function (PCRF), which dictate how traffic should be treated (e.g., bandwidth limits, QoS marking) and how it should be accounted for billing. The PGW performs deep packet inspection, packet filtering, and lawful interception. It also acts as the mobility anchor for the user plane when the UE moves between different SGWs, ensuring session continuity. For non-3GPP accesses (like Wi-Fi via S2a/b/c interfaces), the PGW serves as a common anchor, enabling seamless mobility between 3GPP and trusted/untrusted non-3GPP networks.
In operation, when a UE attaches to the network, the MME selects a PGW based on the Access Point Name (APN) requested by the UE or subscribed in the HSS. The PGW then establishes a default bearer for that PDN connection, assigning an IP address and applying default QoS and charging characteristics. As applications on the UE generate traffic, the PGW applies the appropriate Traffic Flow Templates (TFTs) to route packets to the correct bearer, enforces QoS policies (setting DSCP markings), and generates charging data records (CDRs) for offline or online charging systems. It is the ultimate router for UE-originated packets heading to the internet and the first point of entry for packets destined for the UE.
Purpose & Motivation
The PGW was created as part of the 'System Architecture Evolution' (SAE) to address limitations of the pre-LTE GPRS core network. In 2G/3G GPRS, the gateway functions were split between the SGSN (control) and the GGSN (gateway). The GGSN was often a bottleneck and complex to scale. The EPC architecture aimed for a flatter, all-IP network with reduced latency and higher throughput to support LTE's advanced radio capabilities. The PGW consolidated and enhanced the gateway functions, separating the control and user planes more clearly and enabling more flexible policy enforcement.
It solves several key problems. First, it provides a stable anchor point for mobility, hiding the UE's movement within the radio access network from the external PDN. The UE's IP address, assigned by the PGW, remains constant even as it changes cells or SGWs. Second, it enables sophisticated, real-time policy control. By integrating with the PCRF, operators can implement service-aware charging and QoS (e.g., prioritizing VoIP traffic, throttling peer-to-peer traffic), which was more cumbersome in earlier architectures. Third, it simplifies integration of multiple access technologies (LTE, 3G, Wi-Fi) by providing a single, consistent IP anchor point. Its creation was motivated by the need for a high-performance, scalable, and policy-rich core network to unlock the potential of mobile broadband and enable new revenue-generating services.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (47 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the PGW function was formally split into separate control (PGW-C) and user plane (PGW-U) functions as part of the Control and User Plane Separation (CUPS) architecture, introducing the new Sxb interface between them. This enabled the PGW-C to select and control one or more PGW-U instances, while maintaining support for combined SGW/PGW deployments and interworking with non-split networks. Specific enhancements included defining the PGW pause of charging procedure and ensuring support for GTP-based interfaces for the separated functions.
- Enable SGW-C & PGW-C selection of UPF to take UE's NR capabilities into account TS 23.214CR0047
- SGW/PGW selection for NR TS 29.244CR0033
- Condition correction for SGW-U/PGW-U selection based on DCNR TS 29.244CR0069
- Selection of SGW-C/PGW-C for Dual Connectivity with NR TS 29.244CR0076
- Correction on the support of PGW Pause of Charging TS 29.244CR0181
- GTP-C Extensions for SGW-U and PGW-U selection with CUPS TS 29.274CR1825
+ 11 more changes
In Release 16, the PGW function was formally split into separate control (PGW-C) and user plane (PGW-U) functions, introducing the new Sxb interface between them. This release provided the detailed functional split, specifying which session management and policy enforcement tasks are performed by each separated entity. Furthermore, it defined procedures for PGW-C selection and its control over the PGW-U, including during the Create Session Request message flow.
In Release 17, key enhancements for the PGW function focused on improving reliability and flexibility for its Control Plane (PGW-C) component, particularly in deployments using a combined SGW/PGW architecture or during node changes. New procedures were introduced, such as the restoration of PDN connections for a combined SGW/PGW set and support for PGW-C/SMF change, including mechanisms like using an Alternative PGW-C/SMF FQDN for discovery. These updates also included specific support for PGW reselection for 5G Network Slices and corrections to interfaces like Sxa and Sxb within the separated control and user plane architecture.
- Restoration of PDN connections served by a combined SGW/PGW in a Set TS 29.274CR2029
- New SGW IP Address when moving PDN connections for a combined SGW/PGW/SMF set TS 29.274CR2042
- ePDG support of Restoration of PDN connections after a PGW-C/SMF change TS 29.274CR2049
- Correction to LI Architecture for the SGW/PGW TS 33.127CR0132
- Corrections to LI for combined SMF+PGW-C TS 33.127CR0170
- Correction to HSS-based and PCRF-based P-CSCF restoration TS 23.380CR0117
+ 8 more changes
In Release 18, enhancements for the PGW function focused on improving reliability and clarity during PGW-C/SMF changes and restarts. Specific updates included clarifications and corrections for the restoration of PDN connections after a PGW-CSMF change, support for the PGW-C/SMF Set feature over the S11 interface, and refinements to messages like the PGW Restart Notification Acknowledge and Create Session Request/Response. These changes also covered encoding details for the PGW FQDN IE and the inclusion of the PGW Node Name in the Create Session Response message.
- PGW Change Info TS 29.274CR2057
- Clarification on the PGW Restart Notification Acknowledge message TS 29.274CR2107
- Encoding of PGW FQDN IE TS 29.274CR2072
- PGW-C TEID in Update Bearer Response during PGW triggered PDN connection restoration TS 29.274CR2076
- Corrections to Restoration of PDN connections after a PGW-CSMF change TS 29.274CR2078
- Support of PGW-C/SMF Set feature over S11 TS 29.274CR2094
+ 2 more changes
In Release 19, key enhancements for the PGW function introduced a PCRF/PCF-based restoration solution for EPC/5GC Network Function failure, specifically enabling IMS restoration procedures after a PCRF/PCF failure. This included new support conditions for these IMS restoration processes and allowed the P-CSCF to trigger SMF/PGW-C failure checking. The release also provided clarifications on the enhanced H.248 MOD request for the existing PCRF/PCF bypass procedure.
- Add the PCRF/PCF-based restoration solution for EPC/5GC NF failure TS 23.380CR0128
- P-CSCF triggering SMF/PGW-C failure checking TS 23.380CR0129
- IMS restoration procedure after PCRF/PCF failure TS 23.380CR0130
- Add new condition to support IMS restoration procedures after PCRF/PCF failure TS 29.244CR0996
- Add the PCRF/PCF-based restoration solution for EPC/5GC NF failure TS 23.380CR0133
- Clarification on enhanced H.248 MOD request for PCRF/PCF bypass procedure TS 23.380CR0139
Explore further
Broader topics and technologies where PGW plays a role.
Defining Specifications
3GPP specifications that define or reference PGW, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.214 vj00 | Control and User Plane Separation for EPC | Rel-19 |
| TS 23.380 vj10 | IMS Restoration Procedures | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.799 ve00 | Study on Next Generation System Architecture | Rel-14 |
| TS 23.857 vb00 | EPC Node Failure & Restoration Study | Rel-11 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | 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 29.281 vj20 | GTPv1-U Protocol Specification | Rel-19 |
| TS 29.303 vj10 | DNS Procedures for Evolved Packet System | Rel-19 |
| TS 32.867 vf10 | Management Impacts of EPC CUPS | Rel-15 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | Rel-19 |