Description
The Event Charging Function (ECF) is a fundamental logical entity within the 3GPP Online Charging System (OCS) architecture, as defined in the TS 32.2xx series specifications. It operates in real-time, performing immediate rating and charging for network resource usage as service events occur. The ECF is responsible for processing 'charging events' triggered by network functions like the MSC, SGSN, GGSN, P-CSCF, or AS. A charging event represents a discrete unit of service consumption, such as the establishment of a voice call, the sending of an SMS, a data session activation, or the delivery of a content download. The ECF's primary role is to determine the monetary or non-monetary cost of such an event and to authorize it based on the user's account balance in the OCS.
The ECF interacts with other OCS components through the standardized Ro reference point (Diameter protocol). When a network element (acting as a Charging Trigger Function, CTF) detects a billable event, it sends a Credit Control Request (CCR) to the ECF. The ECF then engages with the Account Balance Management Function (ABMF) to check the subscriber's account balance and with the Rating Function (RF) to determine the cost of the requested service unit. Based on this information, the ECF makes an authorization decision. If credit is available, it reserves an appropriate amount from the balance and responds with a Credit Control Answer (CCA) granting a quota of units (e.g., seconds of call time, volume of data in bytes, number of messages). The network element then allows the service to proceed and consumes this quota. Upon quota exhaustion or service termination, a new CCR is sent, and the ECF deducts the used amount from the account and may grant a new quota. This process ensures real-time balance control.
Architecturally, the ECF can be deployed in different models. In the 'Event-Based Charging' model, it handles immediate, discrete events like SMS or MMS. It also plays a key role in 'Session-Based Charging' through its integration with the Session Charging Function (SCF), where it may handle specific events within a longer session. The ECF is central to enabling prepaid services, real-time spending limit controls (e.g., for data bundles), and convergent charging where services from multiple domains (voice, data, messaging) draw from a single balance. Its operation is critical for operators to prevent revenue leakage, offer flexible tariff plans, and provide subscribers with immediate feedback on their credit consumption.
Purpose & Motivation
The ECF was created to address the fundamental business requirement for real-time, or 'online', charging and prepaid services in mobile networks. Traditional 'offline' charging (based on CDRs) introduced a delay between service usage and billing, which was unsuitable for prepaid subscribers who need immediate deduction from their account balance to prevent debt. Prior to standardized OCS architectures, vendors implemented proprietary prepaid solutions that were tightly coupled with specific network switches, limiting flexibility and interoperability.
The standardization of the ECF within the 3GPP OCS framework, starting in Release 5, solved these problems by decoupling the charging logic from the network elements. It established a clear, open interface (Ro) for all network functions to request credit authorization in a consistent manner. This allowed for the creation of a centralized, real-time charging platform that could serve multiple services (circuit-switched, packet-switched, IMS) from a single subscriber balance. The ECF enabled operators to launch sophisticated prepaid offerings, implement real-time spending controls for postpaid users, and rapidly introduce new services with complex event-based tariffs. It was a key enabler for the prepaid business model that drove massive mobile adoption globally and remains essential for modern convergent charging.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (34 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-5, normative work from Rel-15.
In Release 15, the Event Charging Function (ECF) was enhanced through improvements to charging correlation and parameter handling. Specifically, the release introduced enhanced UE location description for IMS charging over WLAN and resolved issues regarding the Access Network Charging Identifier. These changes provided more precise charging information for network-initiated events and sessions involving application servers.
In Release 16, key enhancements for the Event Charging Function (ECF) included the formal introduction of a service-based charging interface for IMS and mechanisms for improved CHF selection. The updates also refined the general description of IMS charging and the procedures for charging triggers, such as clarifying how charging function addresses are provisioned and handled between network entities like the S-CSCF and Application Servers.
In Release 17, the Event Charging Function (ECF) was enhanced through the introduction of a converged charging architecture specifically for the IMS, integrating online and offline charging. Key updates included the formalization of the Charging Server role as a SIP Application Server performing the ECF function and clarifications on transporting charging parameters like ICID and charging function addresses to Application Servers via third-party REGISTER requests. The release also added details on CDR handling and the selection of charging services within this new IMS converged charging framework.
- Adding data description for IMS converged charging TS 32.260CR0405
- Add service based architecture for offline charging TS 32.260CR0407
- Add IMS offline only charging information TS 32.260CR0410
- Update of converged charging trigger tables using IMS node TS 32.260CR0412
- Addition of converged charging IMS information TS 32.260CR0413
- Clarify Charging service selection TS 32.260CR0415
+ 9 more changes
In Release 18, the Event Charging Function (ECF) was enhanced to support duration-based charging for the IMS data channel, introducing a new charging principle and a specific termination process for these sessions. This release also added capabilities for IMS Charging Diagnostics to improve charging system observability. These updates specifically extended the online charging interactions between the S-CSCF, Application Servers, and the Charging Server that acts as the ECF.
In Release 19, the Event Charging Function (ECF) was enhanced to support duration-based charging for the standalone IMS Data Channel (DC). Furthermore, specific charging principles and information were defined for new services, including IMS DC application download charging, UE-satellite-UE communication, and Avatar communication, necessitating updates to the associated charging architecture and message flows.
- Rel-19 CR 32.260 Support duration-based charging for standalone IMS data channel TS 32.260CR0438
- Rel-19 CR 32.260 Charging architecture for IMS DC application download charging charging TS 32.260CR0439
- Rel-19 CR 32.260 Charging principle for IMS DC application download charging TS 32.260CR0440
- Rel-19 CR 32.260 Charging information for IMS DC application download charging TS 32.260CR0441
- Add charging principle for UE-satellite-UE communication TS 32.260CR0443
- Add charging trigger and charging information for UE-satellite-UE communication TS 32.260CR0444
+ 3 more changes
Explore further
Broader topics and technologies where ECF plays a role.
Defining Specifications
3GPP specifications that define or reference ECF, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.218 vj00 | IMS Call Model Specification | Rel-19 |
| TS 23.815 v1500 | IMS Charging Implications | Rel-5 |
| TR 23.979 vj00 | PoC over 3GPP Systems Architectural Requirements | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 32.260 vj10 | IMS Charging Management | Rel-19 |
| TS 32.273 vj00 | MBMS Charging Management | Rel-19 |