Description
The Charging Gateway Functionality (CGF) is a core component within the 3GPP charging architecture, specifically defined for offline charging. It operates as an intermediary between the network elements that generate charging events and the billing system (or billing domain). Network elements, such as the SGSN, GGSN, P-GW, or S-GW, generate raw charging data in the form of Charging Data Records (CDRs) or partial CDRs. These elements send this data to the CGF using standardized interfaces, primarily the Ga reference point. The CGF's primary technical role is to act as a concentrator and mediator. It receives these CDRs, performs correlation if multiple partial records belong to a single service session (e.g., correlating SGSN and GGSN records for a single PDP context), and assembles them into complete, validated CDRs. It also buffers records to ensure reliable delivery, handles failures and retransmissions, and forwards the consolidated CDR files to the billing system via the Bx reference point, typically using protocols like FTP or FTPS.
Architecturally, the CGF can be implemented as a standalone network node or integrated with other charging functions. In early 3GPP releases, it was a distinct logical function. Its internal components include interfaces for Ga and Bx, a CDR processing and correlation engine, persistent storage for buffering, and management functions for monitoring its performance and load. The CGF ensures data integrity and sequence, which is vital for accurate billing. It may also perform format conversion, translating the CDRs from the ASN.1-encoded format used over Ga into a format suitable for the billing domain, such as a comma-separated value (CSV) file or a specific proprietary format.
The CGF's operation is crucial for the offline charging paradigm, where charging information is collected after the service is rendered. It provides a single point of collection for the network, simplifying the billing system's integration. By handling reliability and correlation, it shields the billing domain from the complexities and potential instabilities of the real-time network elements. This separation of concerns allows network elements to focus on service delivery while the CGF manages the charging data logistics. In modern networks, especially with the introduction of 5G and the Charging Function (CHF), the principles of the CGF are embodied within the Charging Trigger Function (CTF) and Charging Data Function (CDF) for offline charging, but the CGF as a standalone gateway concept remains foundational for legacy and convergent billing systems.
Purpose & Motivation
The CGF was created to address the growing complexity of billing in mobile packet-switched networks introduced with GPRS and 3G. Prior to its standardization, network operators faced significant challenges in collecting usage data from multiple, distributed network elements (like SGSNs and GGSNs) reliably. These elements could generate vast amounts of charging data, and a direct, point-to-point connection from each element to the billing system was inefficient, unreliable, and difficult to scale. The billing systems were not designed to handle the potential data loss, network congestion, or the need for correlation of records from different nodes. The CGF solved this by introducing a dedicated gateway function.
Its creation was motivated by the need for a standardized, robust, and scalable intermediary. The CGF centralizes the collection point, allowing network elements to send data to a nearby or logically centralized gateway using a lightweight protocol (like GTP' over Ga). This reduces the load and connection complexity on the billing system itself. It solves the problem of data reliability through buffering and retransmission mechanisms, ensuring that no charging data is lost due to temporary network or billing system failures. Furthermore, it addresses the critical issue of correlation. A single user session (like web browsing) often involves multiple network nodes; the CGF correlates the partial CDRs from these nodes into a single, coherent record that accurately represents the entire service usage, which is essential for correct billing.
Historically, the CGF enabled the commercial viability of data services by providing a dependable mechanism to monetize packet data usage. It separated the transport and mediation of charging data from the actual billing logic, allowing both domains (network and business support systems) to evolve independently. This architectural choice future-proofed the charging infrastructure, supporting the explosion of data services from 2.5G through to 4G and forming the conceptual basis for charging in 5G systems.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (399 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the CGF was enhanced to support the new 5G architecture, including the introduction of 5G converged charging and the new Bd reference point for 5G charging. The release also expanded charging support for new functionalities like the SMSF in the 5GS architecture and for secondary RAT usage in offline charging. Furthermore, it introduced new northbound APIs, specifically the NAPS API, for charging management.
- Accessing MTC-IWF functionality via T8 TS 23.682CR0281
- Charging management at SCEF and at T8 for MONTE procedures TS 23.682CR0320
- Introduce the Northbound API charging TS 32.240CR0394
- Introduction of 5G in charging architecture TS 32.240CR0396
- Introduction of 5G converged charging TS 32.240CR0397
- Introduction of 5G in charging mechanisms TS 32.240CR0399
+ 32 more changes
In Release 16, the Charging Gateway Functionality was enhanced with a comprehensive framework for offline-only charging, including its introduction for the SMF, flow-based charging, and QoS flow-based charging. The release also defined specific charging information and procedures for interworking with the EPC and added new charging requirements, principles, and triggers for the I-SMF. Furthermore, it introduced the AMF into the charging architecture and provided detailed message formats for offline charging.
- Introduction of AMF in charging architecture TS 32.240CR0409
- Introduce description of volume based charging for VoLTE in PS TS 32.251CR0514
- Add offline only charging TS 32.255CR0035
- Add offline only charging for SMF TS 32.255CR0036
- Add offline only charging CDR generation TS 32.255CR0038
- Add description of charging information for offline only charging TS 32.255CR0039
+ 52 more changes
In Release 17, the CGF was enhanced to support new 5G service capabilities, specifically introducing charging architectures and requirements for 5G LAN services and Ultra-Reliable Low Latency Communication (URLLC). The release added detailed procedures for URLLC charging, including quota management, usage reporting, and PDU session modification message flows. Furthermore, the charging architecture was expanded to support Edge Computing and Local Breakout scenarios.
- Add PGW in logical ubiquitous charging architecture- service based interface TS 32.240CR0413
- Introduction of 5G DDNMF in charging architecture for 5GS TS 32.240CR0429
- Addition of the 5G LAN service charging TS 32.240CR0434
- Charging architecture for Local Breakout TS 32.240CR0439
- Addition of the architecture for 5G LAN charging TS 32.240CR0442
- Enhance charging architecture for Edge Computing TS 32.240CR0443
+ 96 more changes
In Release 18, the CGF was enhanced with new charging support for several key 5G services and architectures. Specifically, it added charging functionality for 5G Multicast/Broadcast Services (5MBS), Time-Sensitive Networking (TSN) services, and 5G satellite access. The release also introduced slice-aware charging for roaming partners and expanded business-to-business (B2B) charging principles and architecture.
- Adding New Consumer for MMS in Charging Architecture TS 32.240CR0446
- Slice-aware charging for Roaming partners TS 32.240CR0467
- Add MB-SMF in charging architecture for 5GS TS 32.240CR0470
- Add charging support for TSN service TS 32.240CR0473
- Add annex for B2B charging TS 32.240CR0474
- Update B2B charging principles TS 32.240CR0475
+ 105 more changes
In Release 19, the CGF saw significant enhancements for new satellite and network sharing scenarios. Key additions included charging support for UE-Satellite-UE communication in IMS, store-and-forward satellite operations for SMS and UP CIoT, and specific architectures for MOCN and MVNOs providing satellite service. The release also introduced charging for AIoT services, disaster roaming, UAS principles, and volume-based charging for the standalone IMS data channel.
- Support of UE-Satellite-UE communication in IMS - Functionality TS 23.228CR1428
- Addition of mobility functionality for Support of UE-Satellite-UE communication in IMS TS 23.228CR1561
- Clean-up of functionality at call setup for Support of UE-Satellite-UE communication in IMS TS 23.228CR1562
- Rel-19 CR 28.201 Add charging architecture for MOCN TS 28.201CR0017
- Rel-19 CR 28.201 Add charging requirement for MOCN TS 28.201CR0018
- Rel-19 CR 28.201 Addition of charging information for MOCN TS 28.201CR0023
+ 80 more changes
In Release 20, the Charging Gateway Functionality was updated to support new charging aspects for multi-modality services and to address the charging impacts from enhanced QoS handling in XRM. The release also included corrections to the descriptions for QoS flow based charging and to the handling of the PDU Session ID for V-SMF charging in EPS-5GS interworking scenarios.
- Add informatin elements to support charging aspects of multi-modality service TS 32.255CR0606
- Rel-20 TS 32.255 Add information elements to address charging impacts from enhanced QoS handling in XRM TS 32.255CR0616
- Rel-20 CR 32.255 Correct some descriptions on QoS flow Based Charging TS 32.255CR0619
- Rel-20 CR 32.255 Correction on PDU Session ID Handling for V-SMF Charging in EPS–5GS Interworking TS 32.255CR0622
Explore further
Broader topics and technologies where CGF plays a role.
Defining Specifications
3GPP specifications that define or reference CGF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.060 vj00 | GPRS Service Description Stage 2 | Rel-19 |
| TS 23.125 v1700 | Flow Based Charging Architecture | Rel-7 |
| TS 23.228 vj50 | IMS Stage-2 Service Description | Rel-19 |
| TS 23.682 vj30 | 3GPP TS 23682: MTC Architecture Enhancements | Rel-19 |
| TS 23.815 v1500 | IMS Charging Implications | Rel-5 |
| TR 23.923 v1300 | Mobile IP+ Feasibility Study for UMTS/GPRS | Rel-4 |
| TS 28.201 vj20 | 5G Network Slice Performance Analytics Charging | Rel-19 |
| TS 28.203 vi10 | Charging management | Rel-18 |
| TS 28.204 vi11 | Charging management | Rel-18 |
| TS 28.702 vj00 | Core Network NRM IRP Information Service | Rel-19 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.250 vj00 | Circuit Switched Offline Charging | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.253 vj00 | Charging for Control Plane Data Transfer | Rel-19 |
| TS 32.254 vj21 | Charging for Northbound APIs | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.256 vj40 | 5G Connection & Mobility Charging Spec | Rel-19 |
| TS 32.260 vj10 | IMS Charging Management | Rel-19 |
| TS 32.270 vj00 | MMS Charging Management Specification | Rel-19 |
| TS 32.271 vj20 | 3GPP LCS Charging Management Spec | Rel-19 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.273 vj00 | MBMS Charging Management | Rel-19 |
| TS 32.277 vj20 | Charging Management for Proximity Services (ProSe) | Rel-19 |
| TS 32.278 vj00 | Monitoring Events Offline Charging Specification | Rel-19 |
| TS 32.279 vj00 | 5G MBS Session Converged Charging | Rel-19 |
| TS 32.280 vj00 | Advice of Charge (AoC) Framework | Rel-19 |
| TS 32.293 vj00 | Proxy Function in Domestic Service Provider | Rel-19 |
| TS 32.295 vj00 | 3GPP Charging: CDR Transfer via GTP' Protocol | Rel-19 |
| TS 32.296 vj00 | Online Charging System (OCS) Architecture | Rel-19 |
| TS 32.297 vj00 | Charging Data Record File Transfer | Rel-19 |
| TS 32.298 vj30 | Charging Data Record (CDR) Parameter Specification | Rel-19 |
| TS 32.632 vb00 | Core Network Resources IRP: Network Resource Model | Rel-11 |
| TS 32.732 vb00 | IMS Network Resource Model IRP: Information Service | Rel-11 |
| TS 32.808 v1800 | Common User Profile Storage Framework | Rel-8 |
| TS 32.825 va00 | Study on Rc Reference Point for ABMF | Rel-10 |