Description
The Offline Charging System (OFCS) is a fundamental component of the 3GPP charging architecture, specifically designed for non-real-time billing scenarios. It operates on the principle of collecting detailed usage information from various network elements after a service has been delivered. The primary data unit is the Charging Data Record (CDR), which is generated by Charging Trigger Functions (CTFs) embedded within network nodes like the SGSN, GGSN, P-GW, or S-CSCF. These CTFs detect chargeable events—such as the start, modification, or end of a data session, voice call, or SMS—and compile the relevant information into a CDR. This record contains fields like the subscriber's identity (e.g., IMSI, MSISDN), session details (start/stop times, duration), service identifiers, and data volume consumed.
The architecture of OFCS is defined by the Charging Data Function (CDF) and the Charging Gateway Function (CGF). The CDF receives the charging events from the CTFs via the Rf reference point, which uses the Diameter base protocol with the Diameter Credit Control Application (DCCA). The CDF validates, formats, and assembles these events into complete, consistent CDRs. These CDRs are then transferred to the CGF via the Ga reference point, typically using protocols like FTP or FTPS. The CGF acts as a gateway, performing functions such as CDR buffering, consolidation, correlation (e.g., linking partial records from different nodes for a single session), and error handling before forwarding the finalized CDRs to the operator's Billing Domain (BD) for long-term storage and invoice generation.
OFCS supports multiple service domains, including Circuit Switched (CS) telephony, Packet Switched (PS) data, and IP Multimedia Subsystem (IMS) services, allowing for converged billing. Its role is strictly offline; it does not interact with online account balances or perform real-time credit authorization. This separation from the Online Charging System (OCS) allows for flexible billing models like monthly subscriptions, volume-based tariffs, and detailed itemized billing. The system's design ensures reliability and non-repudiation of charging data, which is critical for operator revenue assurance and regulatory compliance.
Purpose & Motivation
The OFCS was created to address the fundamental business need for accurate, reliable, and detailed billing of telecommunications services in post-paid subscription models. Prior to standardized offline charging, operators relied on proprietary systems that made interoperability complex and multi-vendor network deployments difficult. The 3GPP standardization of OFCS, beginning in Release 6, provided a unified framework for collecting usage data from all network domains, enabling operators to bill for a wide array of services—voice, data, messaging, and multimedia—from a single, consistent platform.
Its creation was motivated by the limitations of real-time charging for all services. While online charging is necessary for prepaid services, it introduces latency and complexity for services where immediate credit control is not required. OFCS solves this by decoupling the billing process from the service delivery path. This allows the network to deliver services without pausing to check credit, improving user experience and network efficiency for post-paid customers. It also enables the generation of detailed, auditable records essential for customer invoices, business intelligence, fraud detection, and regulatory reporting. The system's evolution has been driven by the need to support new services, higher data volumes, and more complex charging scenarios introduced in later 3GPP releases.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (52 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-6, normative work from Rel-15.
In Release 15, the primary introduction for the Offline Charging System (OFCS) was its integration within the new 5G charging architecture, as part of the broader introduction of 5G in charging mechanisms and a converged charging framework. This included defining its role in the high-level overall charging architecture to support 5G systems. Specific enhancements, such as updates to support the SMSF in the charging architecture for 5GS, were also introduced to extend offline charging capabilities to new 5G network functions.
- 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
- Introduce the 5G charging in clause 3 TS 32.240CR0401
- Charging mode clarifications in Converged Charging System TS 32.240CR0402
+ 4 more changes
In Release 16, the key update for the Offline Charging System (OFCS) was the introduction of the AMF (Access and Mobility Management Function) into the charging architecture. This change integrated the 5G core network's mobility management function into the offline charging framework, enabling the generation of Charging Data Records (CDRs) for its chargeable events. The OFCS then collects and processes these records for delivery to the Billing Domain.
- Introduction of AMF in charging architecture TS 32.240CR0409
In Release 17, the Offline Charging System (OFCS) architecture was enhanced to support new 5G capabilities, including the formal introduction of the 5G DDNMF (Data Delivery Network Management Function) and charging for 5G LAN services. The release also updated the logical ubiquitous charging architecture and provided architectural corrections and clarifications for areas like Network Slice charging and Edge Computing. These updates ensured the offline charging mechanism, which collects charging information without affecting the service in real time, remained aligned with the evolving 5G system.
- 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
+ 7 more changes
In Release 18, the Offline Charging System (OFCS) was enhanced with new architectural support for several 5G services, including charging for TSN (Time-Sensitive Networking) services and 5G Satellite access. The release also expanded B2B (Business-to-Business) charging with updated principles and architectural clarifications, and introduced slice-aware charging for roaming partners. Furthermore, new specific consumers were added to the charging architecture, such as for MMS and the MB-SMF (Multicast/Broadcast SMF).
- 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
+ 10 more changes
In Release 19, the Offline Charging System (OFCS) was extended with new charging principles and architectural support for several emerging services. Key additions include charging support for AIoT (AI and IoT) services, the integration of the Gateway Mobile Location Centre (GMLC) into the 5GS charging architecture, and specific charging frameworks for Unmanned Aircraft Systems (UAS) and disaster roaming scenarios. The release also introduced charging capabilities for MVNOs providing satellite service and clarified aspects of the converged charging refund mechanism.
- Introduction of GMLC in charging architecture for 5GS TS 32.240CR0491
- Rel-19 CR 32.240 Add charging support to AIoT service TS 32.240CR0510
- Rel-19 CR 32.240 CAPIF Logical Charging Architecture TS 32.240CR0511
- Rel-19 CR 32.240 CAPIF Service Charging TS 32.240CR0512
- Add charging principles for UAS TS 32.240CR0517
- Add MVNO charging which provides satellite service TS 32.240CR0518
+ 6 more changes
Explore further
Broader topics and technologies where OFCS plays a role.
Defining Specifications
3GPP specifications that define or reference OFCS, 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 23.125 v1700 | Flow Based Charging Architecture | Rel-7 |
| TS 23.203 vj20 | Policy and charging control architecture | Rel-19 |
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 29.212 vj00 | Gx/Gxx/Sd/St Diameter Protocol | Rel-19 |
| TS 29.215 vj00 | S9 Reference Point Stage 3 Specification | Rel-19 |
| TS 29.219 vj00 | Sy Reference Point Stage 3 Specification | Rel-19 |
| TS 29.817 vc10 | Study on XML-based Rx interface for PCC | Rel-12 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.280 vj00 | Advice of Charge (AoC) Framework | Rel-19 |
| TS 32.820 v1801 | Charging Architecture Study for Evolved 3GPP | Rel-8 |
| TS 32.869 vf00 | Diameter Overload Control for Charging Interfaces | Rel-15 |