Credit Control

Description

Credit control is a fundamental mechanism in 3GPP online charging systems that enables real-time interaction with a subscriber's account to manage service usage charges. It is defined in 3GPP TS 32.240 and related specifications, and is a key component of the Charging Architecture. The mechanism ensures that services are only provided if sufficient credit is available, thereby preventing revenue loss and enabling prepaid and postpaid services with real-time balance management.

The credit control process involves several steps: first, a check is performed to determine if the subscriber has sufficient credit for the requested service. If credit is available, a reservation is made, allocating a portion of the credit for the anticipated service usage. As the service is consumed, the reserved credit is gradually deducted. Upon service completion, the actual charges are deducted from the account, and any unused reserved credit is refunded. This process is typically executed by the Online Charging System (OCS) in conjunction with network elements such as the PCEF (Policy and Charging Enforcement Function) or the SMF (Session Management Function) in 5G.

The credit control mechanism is standardized across various network domains, including IMS, EPS, and 5G, and supports multiple service types such as data, voice, and messaging. It relies on the Gy reference point for online charging in EPS and the Nchf reference point in 5G, using protocols like Diameter and HTTP/2. The mechanism is extensible to support multiple services and tariff models, including time-based, volume-based, and event-based charging.

Credit control is crucial for operators to offer flexible pricing plans, such as prepaid, postpaid with spending limits, and pay-as-you-go. It also enables real-time fraud prevention and credit risk management. The 3GPP specifications define the credit control application in TS 32.251 (PS domain), TS 32.271 (CS domain), TS 32.272 (IMS), TS 32.276 (MMS), TS 32.277 (LCS), and TS 32.293 (common).

In summary, credit control is a real-time charging mechanism that ensures subscribers are charged accurately and only for the services they consume, while enabling operators to manage credit risk and offer diverse pricing models.

Purpose & Motivation

Credit control exists to enable real-time charging and credit management in telecommunications networks. Before its introduction, charging was primarily offline, meaning that services were provided without immediate verification of the subscriber's ability to pay, leading to potential revenue loss and fraud. Credit control solves this by interacting with the subscriber's account in real-time to authorize and reserve credit before service delivery.

The motivation for credit control came from the need to support prepaid services, where subscribers pay in advance and require immediate deduction of charges as they use services. It also addresses the need for spending limits in postpaid scenarios, allowing operators to control credit risk. The mechanism was standardized in 3GPP Release 8 as part of the evolved charging architecture, building on earlier offline charging systems.

Credit control provides a standardized framework for online charging across different network domains and service types, ensuring interoperability between vendors and enabling operators to offer innovative services with real-time charging. It has evolved over releases to support new services and technologies, such as 5G and network slicing.