Charging Tariff Information

Description

Charging Tariff Information (CRGT) is a critical data element defined within the 3GPP specifications for online charging. It functions as a container or information element that conveys the specific pricing rules and conditions applicable to a network resource usage event, such as voice calls, data sessions, or SMS messages. The CRGT is transported within Diameter-based charging protocols, primarily between network functions like the Policy and Charging Rules Function (PCRF) or the Application Function (AF) and the Online Charging System (OCS). Its structure is designed to be extensible, carrying attributes like tariff times (e.g., peak/off-peak rates), tariff currencies, rate elements (cost per unit), and conditions for tariff switching.

Architecturally, CRGT operates within the 3GPP Policy and Charging Control (PCC) framework. When a user initiates a service, the network triggers a charging request. The relevant network function (e.g., PCRF via the Gx interface or AF via the Rx interface) may include or reference CRGT within the Diameter Credit-Control-Request (CCR) message sent to the OCS. The OCS, which maintains subscriber balances and rating functions, parses the CRGT to apply the correct tariff. This allows the OCS to calculate the monetary cost or the number of service units to be deducted from the user's account before granting quota for the service. The OCS then responds with a Credit-Control-Answer (CCA) containing the granted quota, influenced by the tariff evaluation.

The key components of CRGT are its attribute-value pairs (AVPs) as defined in the Diameter base protocol and 3GPP extensions. These AVPs can specify the tariff information in detail, including the Tariff-Time-Change AVP (indicating when a tariff change occurs), the Tariff-Change-Usage AVP (defining the usage threshold for a tariff change), and currency codes. This granularity supports complex billing models like tiered pricing, time-of-day discounts, and volume-based rates. Its role is to decouple tariff logic from the core charging transaction, allowing operators to update pricing schemes in the OCS or PCRF without altering the protocol between network elements, thereby enhancing operational flexibility.

In practice, CRGT enables real-time, session-aware charging. For example, during a data session, the PCRF may inform the OCS that the first 100MB is charged at one rate (tariff 1) and any subsequent usage at a different rate (tariff 2), with the CRGT carrying these conditions. The OCS uses this to monitor usage against the thresholds and switch tariffs dynamically. This mechanism is fundamental for implementing fair usage policies, promotional offers, and sophisticated service plans. It ensures that charging is accurate, transparent, and adaptable to competitive market demands, forming the backbone of monetization in mobile networks.

Purpose & Motivation

CRGT was introduced to address the limitations of earlier, simpler charging mechanisms that could not support the dynamic and complex tariff structures required by modern mobile services. Prior to its standardization, charging often relied on static, pre-configured rates within network elements, making it difficult to implement real-time, context-aware pricing. This was inadequate for the rise of prepaid services, where immediate balance checks and flexible rating are crucial. The creation of CRGT within the 3GPP Online Charging System (OCS) architecture, starting in Release 8, provided a standardized, interoperable way to communicate detailed tariff information across network interfaces, solving the problem of rigid, monolithic billing systems.

Historically, as networks evolved from circuit-switched voice to packet-switched data and IMS-based multimedia services, the need for granular, session-based charging grew. Operators wanted to offer diverse plans—such as time-based discounts, volume tiers, and service-specific rates—without overhauling their entire charging infrastructure for each new offer. CRGT, as part of the Diameter-based Gy and Sy reference points (specified in 29.458 and 29.658), enabled this by separating tariff definition from the charging transaction flow. This allowed the OCS to become a centralized, intelligent rating engine, while network elements could simply relay tariff identifiers or parameters via CRGT, reducing complexity and enabling rapid service deployment.

The technology solves key operational challenges: it ensures billing accuracy by providing explicit tariff details in real-time, supports regulatory requirements for transparent charging, and facilitates innovation in service monetization. By standardizing CRGT, 3GPP ensured that different vendors' OCS, PCRF, and AF components could interoperate seamlessly, fostering a competitive ecosystem. This was motivated by the industry's shift towards all-IP networks and the demand for personalized, flexible consumer and enterprise billing models, which legacy systems could not efficiently handle.

Key Features

• Standardized Diameter AVPs for encoding tariff parameters
• Support for time-based tariff switching (e.g., peak/off-peak rates)
• Enablement of volume-based or usage-tiered pricing models
• Decoupling of tariff logic from core charging protocols for flexibility
• Real-time tariff application within Online Charging System (OCS) decisions
• Interoperability across network functions via 3GPP-defined interfaces

Evolution Across Releases

Defining Specifications