Description
The Offline Charging Function (OCF) is a fundamental element within the 3GPP Charging System, specifically designed for offline (post-paid) charging scenarios. It operates on the principle of collecting resource usage information after the network resources have been consumed. The OCF resides within the Charging Trigger Function (CTF), which is embedded in various network elements like the SGSN, GGSN, MSC, or IMS entities. When a service is rendered, the CTF detects charging-relevant events and generates Charging Data (CD). This data is then sent via the Rf reference point to the Charging Data Function (CDF). The CDF, a key sub-component of the OCF architecture, is responsible for assembling the received charging events into coherent, session-based Charging Data Records (CDRs). These CDRs are formatted according to 3GPP specifications and contain detailed information such as subscriber identity, service used, data volume, duration, timestamps, and serving network element. The CDF then forwards the completed CDRs via the Ga reference point to the Charging Gateway Function (CGF). The CGF acts as a gateway, performing tasks like CDR buffering, validation, consolidation, and correlation before ultimately transferring the records to the network operator's Billing Domain (BD) for further processing and invoice generation. The entire OCF process is governed by the offline charging architecture defined in 3GPP TS 32.240, ensuring a standardized, reliable, and auditable flow of charging information from network usage to financial settlement. Its role is passive from the service control perspective, as it does not influence the service delivery in real-time but is crucial for the commercial and operational backend.
Purpose & Motivation
The OCF was created to provide a standardized, reliable, and scalable mechanism for operators to charge customers for network and service usage after the fact (post-paid billing). Prior to standardized offline charging, operators relied on proprietary systems within each network element to log usage, leading to inconsistencies, integration challenges, and difficulties in creating unified customer invoices. The 3GPP-defined OCF architecture solves these problems by establishing a clear separation between the network elements that generate charging events and the centralized functions that process them into billable records. It addresses the critical business need for revenue assurance by ensuring that all chargeable events are captured, accurately recorded, and delivered to the billing system. The creation of the OCF in Release 99 was motivated by the transition to packet-switched services (GPRS) and the increasing complexity of service offerings, which required a more robust and flexible charging framework than what was available for legacy circuit-switched voice. It provides the foundation for itemized billing, billing dispute resolution, and financial reporting.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (224 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
In Release 15, the OCF was fundamentally integrated into the new 5G charging architecture, supporting new capabilities like converged charging and enhancements for network functions such as the SMSF and eFMSS. Key updates included clarifications for roaming, charging identifiers, and the handling of multiple PRAs (Policy and Charging Rules Function Attributes) within offline charging. The release also introduced new standardized charging interfaces, specifically the northbound API and the Bd reference point, to support these expanded 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
+ 15 more changes
In Release 16, the Offline Charging Function (OCF) was significantly enhanced by formally introducing and detailing "offline only charging" as a distinct mechanism across multiple network functions. This included defining specific procedures for offline only charging for the SMF, for flow-based and QoS flow-based charging, and for CHF selection, alongside the addition of detailed message formats and CDR generation rules for this mode. The release also expanded the architecture by introducing the AMF into the charging framework and added charging requirements and principles for the I-SMF.
- 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
+ 36 more changes
In Release 17, the Offline Charging Function (OCF) was enhanced to support new 5G services and architectures. Specifically, the charging architecture was expanded to include 5G LAN services, Edge Computing, and URLLC, introducing new charging requirements, principles, and message flows for these features. Furthermore, the architecture now formally incorporates the 5G DDNMF and addresses charging for 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
+ 54 more changes
In Release 18, the OCF was enhanced to support offline charging for new services including 5G Multicast/Broadcast Services (5MBS), Time-Sensitive Networking (TSN) services, and 5G satellite access. It also introduced new charging principles for Business-to-Business (B2B) scenarios and expanded capabilities for slice-aware charging when dealing with roaming partners. Furthermore, the release added charging support for the MB-SMF within the 5GS architecture and introduced volume-based charging principles for the IMS data channel.
- 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
+ 60 more changes
In Release 19, the OCF was extended with new offline charging principles and information support for emerging services, specifically for AIoT (AI and IoT), CAPIF service exposure, and Unmanned Aircraft Systems (UAS). The release also introduced significant enhancements for satellite connectivity, including charging for store-and-forward operations, MVNO satellite service provision, and dedicated satellite roaming scenarios. Furthermore, new volume-based charging principles were defined for the standalone IMS Data Channel and for application download and usage.
- 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
+ 25 more changes
In Release 20, the Offline Charging Function (OCF) was enhanced to support new charging information elements for multi-modality services and to address the charging impacts from enhanced QoS handling in XRM. The release also included corrections and clarifications to existing procedures, specifically for QoS flow-based charging and for PDU Session ID handling during EPS-5GS interworking scenarios involving V-SMF charging.
- 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 OCF plays a role.
Defining Specifications
3GPP specifications that define or reference OCF, 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 23.057 vj00 | Mobile Execution Environment (MExE) Specification | Rel-19 |
| TS 23.125 v1700 | Flow Based Charging Architecture | Rel-7 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 32.240 vj40 | Charging Management Architecture & Principles | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 32.255 vk10 | Telecom Management; Charging for 5G Data Connectivity | Rel-20 |
| TS 32.272 vj00 | Charging for Push-to-Talk over Cellular (PoC) | Rel-19 |
| TS 32.278 vj00 | Monitoring Events Offline Charging Specification | Rel-19 |
| TS 32.293 vj00 | Proxy Function in Domestic Service Provider | 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 32.808 v1800 | Common User Profile Storage Framework | Rel-8 |
| TS 32.850 ve00 | IMS Charging Correlation Methods Study | Rel-14 |