Description
The PGW-C (PDN Gateway Control plane function) is a core network function introduced as part of the Control and User Plane Separation (CUPS) architecture in 3GPP Release 14. It represents the decoupling of the traditional P-GW (Packet Data Network Gateway) into separate control plane (PGW-C) and user plane (PGW-U) entities. This separation allows for independent scaling, deployment, and evolution of the control and user plane functions. The PGW-C is responsible for the intelligence and signaling aspects of the gateway.
Architecturally, the PGW-C interfaces with several other core network functions. It communicates with the Policy and Charging Rules Function (PCRF) via the Gx interface to receive policy and charging control (PCC) rules. It interacts with the Online Charging System (OCS) via the Gy interface for online credit control and with the Offline Charging System (OFCS) via the Gz interface for offline charging data record (CDR) generation. For session management, it connects to the Serving Gateway Control plane function (SGW-C) and the Mobility Management Entity (MME) in the Evolved Packet Core (EPC).
Its primary operational role involves managing Packet Data Network (PDN) connections for User Equipment (UE). When a UE attaches to the network and requests a PDN connection, the PGW-C is responsible for session establishment, modification, and termination. It allocates an IP address to the UE (or delegates this to the PGW-U), enforces QoS policies based on PCC rules from the PCRF, and manages charging based on the user's service data flow. It also handles mobility events, such as handovers between different access technologies (e.g., LTE to Wi-Fi), ensuring session continuity.
The PGW-C works in tandem with the PGW-U via a standardized control protocol, defined in 3GPP specifications such as TS 29.244 (PFCP - Packet Forwarding Control Protocol). The PGW-C uses PFCP to instruct the PGW-U on how to handle the user plane traffic. This includes installing, modifying, or deleting packet detection rules (PDRs), forwarding action rules (FARs), QoS enforcement rules (QERs), and usage reporting rules (URR). This master-slave relationship allows the PGW-C to centrally control multiple, potentially distributed, PGW-U instances, enabling flexible and efficient traffic routing and processing.
Purpose & Motivation
The PGW-C was created to address the limitations of the monolithic P-GW architecture used in earlier 3GPP releases. In traditional EPC, the P-GW was a single network node combining both control and user plane functionalities. This monolithic design posed several challenges, including inefficient scaling (the entire node had to be scaled even if only user plane capacity was needed), limited deployment flexibility (control and user plane functions had to be co-located), and hindered innovation (upgrades to one plane could impact the other).
The primary motivation for its creation was the industry-wide drive towards network function virtualization (NFV) and software-defined networking (SDN), which demand disaggregated, software-based components that can be deployed independently. The Control and User Plane Separation (CUPS) architecture, formalized in Release 14, was the 3GPP's response. By splitting the P-GW into PGW-C and PGW-U, operators gained the ability to scale the control plane (which handles signaling and policy) and the user plane (which handles high-throughput data packets) independently based on traffic patterns. For instance, user plane functions could be deployed at the network edge for low-latency services, while control plane functions could remain centralized for efficient management.
This separation also paved the way for the 5G Core (5GC) network architecture, where the Session Management Function (SMF) and User Plane Function (UPF) are direct conceptual successors to the PGW-C and PGW-U, respectively. The introduction of PGW-C allowed for a smoother evolution from EPC to 5GC, enabling early adoption of cloud-native principles and distributed architectures within the 4G network, thus solving the problems of scalability, flexibility, and cost-efficiency in the face of exponentially growing mobile data traffic.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (98 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-14, normative work from Rel-15.
In Release 15, the PGW-C was formally introduced as the new control plane function resulting from the architectural separation of the traditional PGW, as specified for control and user plane separation of EPC nodes. This release defined its core relationship with the PGW-U via the new Sxb reference point and established the PGW-C's role in session management, policy and charging control, and the selection of the User Plane Function (UPF). New capabilities introduced for the PGW-C, as indicated by the Change Requests, include procedures for load and overload control on the N4 interface (the stage 3 realization of Sxb), user plane inactivity reporting, and handling user plane path failure reports.
- Enable SGW-C & PGW-C selection of UPF to take UE's NR capabilities into account TS 23.214CR0047
- Rate control for MO exception data TS 29.061CR0498
- User plane reporting TS 29.244CR0041
- Load-overload control on N4 TS 29.244CR0053
- Reporting User Plane Inactivity on N4 TS 29.244CR0060
- Condition correction for SGW-U/PGW-U selection based on DCNR TS 29.244CR0069
+ 10 more changes
In Release 16, the PGW-C function was enhanced with new PFCP procedures, including an improved PFCP Association Release Procedure and mechanisms for PFCP session reestablishment after a UP function restart. It also gained support for PFCP messages bundling and for PFCP sessions to be successively controlled by different SMFs within the same set. Furthermore, the release introduced capabilities for User Plane Path Recovery Reports and Additional PFCP Session Report Requests.
- Rate control for 5G CIoT TS 29.561CR0005
- Clarification of TEID allocation by gateway user plane TS 23.214CR0074
- Correct small data rate control status TS 29.561CR0017
- Resolve editor note for PLMN rate control TS 29.561CR0024
- Enhancement to the PFCP Association Release Procedure TS 29.244CR0240
- User Plane Forwarding with Control Plane CIoT 5GS Optimisation TS 29.244CR0247
+ 30 more changes
In Release 17, the PGW-C saw enhancements primarily focused on the N4mb interface and PFCP protocol, introducing capabilities like User Plane Inactivity Detection and Reporting, Transport Level Marking for PFCP sessions, and control of Start/Stop Usage Measurement. It also included specific corrections and updates for scenarios involving a combined SMF+PGW-C, PFCP session restoration after a UPF restart, and the handling of PFCP Node Reports. These updates refined the control and reporting mechanisms between the control plane and its associated user plane functions.
- PFCP Node related messages supported over N4mb TS 29.244CR0606
- User Plane (In)Activity Detection and Reporting over N4mb TS 29.244CR0608
- Transport Level Marking information for PFCP sessions over N4mb TS 29.244CR0622
- Corrections to LI for combined SMF+PGW-C TS 33.127CR0170
- 5GS User Plane Node TS 29.244CR0558
- Updates for Bridge/User plane Node ID configuration TS 29.244CR0585
+ 14 more changes
In Release 18, the PGW-C saw updates primarily focused on refining the Packet Forwarding Control Protocol (PFCP) interface with the user plane. Specific enhancements included extensions for handling High Reliability - Single Bidirectional Origin (HR-SBO) PDU sessions, the introduction of Transport Layer (TL) Containers in PFCP Session Modification/Deletion procedures, and the creation of a new Buffering Action Rule (BAR) within the PFCP Session Modification Request. Furthermore, procedures were updated for user plane inactivity detection and timer management, as well as for PFCP error handling and session deletion during SMF handovers.
- Generalization of QoS monitoring control description TS 29.244CR0723
- User plane inactivity detection update TS 29.244CR0731
- PFCP extensions for HR-SBO PDU sessions TS 29.244CR0750
- TL-Containers in PFCP Session Modification/Deletion Request/Response TS 29.244CR0767
- Updates on SMF+PGW-C interworking with DHCP TS 29.561CR0144
- Support NEF playing the role of an MBS AF/AS for user plane MBS group message data delivery TS 29.561CR0149
+ 13 more changes
In Release 19, key enhancements for the PGW-C function focused on improving the reliability and management of the PFCP interface with the user plane. Specifically, new procedures were introduced to exclude certain PFCP sessions from restoration during an SMF failure and to enable the restoration of sessions at an alternative SMF, thereby increasing system resilience. Additionally, the release provided clarifications and corrections for existing mechanisms, such as the User Plane Inactivity Timer and header handling control rules.
- PFCP sessions excluded from the restoration upon a SMF failure with SMF set being deployed TS 29.244CR0895
- Modification of Header Handling Control Rules TS 29.244CR0935
- Providing alternative SMF(s) per PFCP Session TS 29.244CR0911
- GTP-U Path QoS Control Information TS 29.244CR0887
- Restore PFCP Sessions at an alternative SMF TS 29.244CR0914
- User Plane Inactivity Timer clarification TS 29.244CR0971
+ 1 more changes
Explore further
Broader topics and technologies where PGW-C plays a role.
Defining Specifications
3GPP specifications that define or reference PGW-C, 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 28.708 vj00 | EPC NRM Integration Reference Point Information Service | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.244 vj40 | PFCP Specification for Control/User Plane Separation | Rel-19 |
| TS 29.561 vj30 | 5G Interworking with External Data Networks | Rel-19 |
| TS 29.844 ve00 | Control and User Plane Separation for EPC Nodes | Rel-14 |
| TS 32.867 vf10 | Management Impacts of EPC CUPS | Rel-15 |
| TS 33.127 vj50 | Lawful Interception Architecture and Functions | Rel-19 |