Add-on Charge

Description

The add-on charge is a charging concept in 3GPP specifications that allows an additional charge to be applied to a subscriber's session or service, on top of the existing tariff. It is defined in TS 29.458 (Policy and Charging Control (PCC) over Sd reference point), TS 29.658 (Policy and Charging Control (PCC) over Sy reference point), and TS 32.280 (Charging management; Advice of Charge (AoC) service). The add-on charge provides a mechanism to apply supplementary charges for specific events or services without altering the base tariff structure. It can be metered in non-monetary units, such as meter pulses used in legacy telephony, or in monetary units, such as currency amounts. This flexibility allows operators to implement various charging models, from traditional pulse-based billing to modern currency-based billing.

In the context of the Policy and Charging Control (PCC) architecture, the add-on charge is typically used in conjunction with the Advice of Charge (AoC) service. The AoC service provides real-time charging information to the user, and the add-on charge can be used to indicate additional costs that are not part of the base tariff. For example, when a user initiates a premium service or roams into a different network, an add-on charge may be applied to reflect the extra cost. The add-on charge is communicated from the charging system to the network element responsible for generating charging information, such as the PCEF or the TDF, which then includes it in the charging records or notifies the user via AoC.

The add-on charge can be applied in both online and offline charging scenarios. In online charging, the add-on charge is reserved and deducted from the user's account in real-time, ensuring that the user is aware of the additional cost before consuming the service. In offline charging, the add-on charge is recorded in Call Detail Records (CDRs) for post-processing and billing. The add-on charge may be triggered by various events, such as the activation of a specific service, the usage of a particular application, or the occurrence of a network event like handover to a different charging zone. The charging system determines the appropriate add-on charge based on the tariff and the event, and then instructs the network to apply it.

Key components of the add-on charge include the charge amount, the unit of measurement (monetary or non-monetary), and the conditions under which it applies. The charge amount can be a fixed value or a rate per unit (e.g., per minute, per megabyte). The unit of measurement determines how the charge is expressed; for example, a meter pulse might represent a fixed increment of cost, while a currency amount is a direct monetary value. The conditions for applying the add-on charge are typically defined in the subscriber's tariff plan or in policy rules. The add-on charge is often used in conjunction with other charging mechanisms, such as the base tariff and discounts, to compute the final charge for a session.

The add-on charge concept has evolved over time. In early releases (Rel-8 to Rel-10), it was defined as a 'single additional charge which does not change the current tariff.' This definition was limited to a single charge and did not specify the metering units. In Release 11, the definition was expanded to clarify that the add-on charge is an additional charge on top of the current tariff and can be metered in non-monetary or monetary units. This change provided more flexibility and clarity for operators implementing diverse charging models. The definition has remained stable since Rel-11, with only minor editorial changes, indicating its maturity and continued relevance in both 4G and 5G networks.

Purpose & Motivation

The add-on charge was created to provide a flexible mechanism for applying supplementary charges to a subscriber's session or service without modifying the base tariff. In traditional charging systems, any additional cost would require a change to the tariff structure, which was cumbersome and inflexible. The add-on charge allows operators to apply temporary or event-based charges, such as a surcharge for premium content, roaming, or peak-hour usage, on top of the existing tariff. This enables more dynamic and granular charging, which is essential for monetizing new services and managing network resources.

Historically, the add-on charge was introduced in 3GPP Release 8 as part of the charging management framework. The initial definition was limited to a single additional charge that did not change the current tariff, which restricted its applicability. As networks evolved and charging models became more sophisticated, the definition was expanded in Release 11 to include metering in non-monetary and monetary units. This change allowed operators to implement a wider range of charging scenarios, from legacy pulse-based billing to modern currency-based billing. The add-on charge thus addresses the need for a standardized, flexible way to apply supplementary charges across different network technologies and charging systems.

The add-on charge also supports the Advice of Charge (AoC) service, which informs users of the cost of a service in real-time. By providing a clear indication of additional charges, the add-on charge helps operators comply with regulatory requirements for transparent charging and enhances the user experience by avoiding bill shock. In summary, the add-on charge exists to enable flexible, transparent, and dynamic charging for supplementary services, solving the limitations of static tariff structures and supporting innovative business models.