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.
Architecture
In the Network Map
- 4G EPC → PGW (Packet Gateways)
Evolution Lineage
- Succeeded by: SMF (4G→5G), UPF (4G→5G)
- Network evolution overview →
Classification
Release Timeline
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (40 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the PGW function was fundamentally re-architected through Control and User Plane Separation (CUPS), introducing distinct PGW-Control (PGW-C) and PGW-User (PGW-U) functions. This split enabled independent scaling and selection of the user plane, with new GTP-C extensions introduced for controlling the PGW-U via the Sxb reference point. Furthermore, the release formalized procedures like PGW pause of charging and detailed the functional split, allowing a combined PGW/SMF entity to be selected for interworking with 5GS.
- 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 primary new aspect for the PGW was its formal architectural split into separate control plane (PGW-C) and user plane (PGW-U) functions, as defined for Control and User Plane Separation (CUPS). This introduced the new Sxb reference point between the PGW-C and PGW-U. Furthermore, the release specified that the PGW-C is responsible for selecting the PGW-U, impacting procedures like the PGW selection and the Create Session Request message.
- PGW Selection and the Create Session Request message TS 29.274CR1978
In Release 17, enhancements for the PGW function focused on improving resilience and flexibility for the separated PGW-C/SMF control plane, particularly in combined SGW/PGW architectures. Key additions included procedures for the restoration of PDN connections after a PGW-C/SMF change, support for PGW-C/SMF reselection for network slices, and mechanisms like the Alternative PGW-C/SMF FQDN for discovery and change support. These changes also introduced specific handling for ePDG interactions and refined the LI architecture for combined nodes.
- 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
- PGW reselection for 5G Network Slice TS 29.274CR2022
+ 7 more changes
In Release 18, enhancements for the PGW function focused on improving the reliability and clarity of procedures 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 information elements in messages like the Create Session Request/Response. Additionally, the release provided more precise encoding rules for the PGW FQDN IE and defined 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, a new procedure was introduced for the PGW-C (PGW Control Plane function) to perform failure checking when triggered by the P-CSCF. This enhancement, based on the specified functional split where the PGW-C controls the PGW-U, adds a specific interaction mechanism for session management related to IMS signaling.
- P-CSCF triggering SMF/PGW-C failure checking TS 23.380CR0129
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 |
