Tariff

Description

In 3GPP charging and billing architecture, a Tariff is a structured set of parameters that determine the cost to a subscriber or third party for using network resources. It defines how charges are calculated based on usage of a particular bearer, session, or service. The tariff is applied by the charging system, which collects usage data from network elements and applies the appropriate tariff to generate a Charging Data Record (CDR) or an online charging session. The tariff can include parameters such as rate per unit of data, time-based charges, event-based charges, and discounts or surcharges based on conditions like time of day, location, or quality of service.

The tariff concept is central to the 3GPP charging architecture, which is specified in a series of Technical Specifications (TS) including 32.240 (Charging architecture and principles), 32.250 (Charging in circuit-switched domain), 32.251 (Charging in packet-switched domain), 32.272 (Charging for IMS), 32.273 (Charging for MMS), 32.276 (Charging for MBMS), 32.278 (Charging for ProSe), 32.280 (Charging for EPC), 32.293 (Charging for 5G), 32.296 (Charging for online charging), and 32.825 (Charging for network slicing). Additionally, 29.458 and 29.658 specify the Diameter-based charging interfaces (e.g., Gy, Ro) used to convey tariff information and usage data.

The tariff is typically managed by the Charging Trigger Function (CTF) within network elements, which detects chargeable events and reports them to the Charging Data Function (CDF) or Online Charging Function (OCF). The CDF/OCF applies the tariff to the usage data to produce a CDR or to authorize/deny a session in online charging. The tariff itself is provisioned by the operator into the charging system, often via the Charging Gateway Function (CGF) or a Business Support System (BSS). The tariff can be dynamic, meaning it can change based on conditions, or static, meaning it is fixed for a given service.

In offline charging, the tariff is applied after the session to generate a CDR, which is then processed by the billing system. In online charging, the tariff is applied in real-time to determine whether the subscriber has sufficient credit to continue the session. The tariff may be based on volume (e.g., per megabyte), time (e.g., per minute), events (e.g., per message), or a combination. It can also include rating groups, which are identifiers that group together chargeable events that share the same tariff.

The tariff concept has evolved with network generations. In 2G/3G, tariffs were primarily based on circuit-switched voice and packet-switched data. In 4G, with the introduction of EPC, tariffs became more granular, supporting QoS-based charging and service-specific tariffs. In 5G, the Service Based Architecture (SBA) and network slicing introduce new charging dimensions, such as slice-based tariffs and network slice as a service. The tariff remains a key tool for operators to monetize their networks and for subscribers to understand the cost of services.

Purpose & Motivation

The Tariff concept exists to provide a standardized and flexible way to define the charges for network usage. Before its formalization, charging systems might have used proprietary or ad-hoc methods to calculate costs, leading to inconsistencies and difficulties in interoperability. The Tariff solves this by defining a common set of parameters that can be understood by different network elements and charging systems, enabling accurate and consistent billing across multi-vendor networks. It allows operators to create complex pricing plans that reflect the value of different services and network conditions.

Historically, as networks evolved from voice-centric to data-centric, the need for more sophisticated charging became apparent. Early charging was based on simple time or volume metrics, but with the advent of IP-based services, operators needed to differentiate charges based on service type, quality of service, and content. The Tariff concept was introduced to support this differentiation, allowing operators to define tariffs per bearer, session, or service. This flexibility is essential for implementing tiered pricing, zero-rating, and other business models.

Furthermore, the Tariff supports both offline and online charging, enabling prepaid and postpaid billing. In online charging, the tariff is used in real-time to control access to services based on the subscriber's balance, which is critical for prepaid users. The evolution of the Tariff definition over releases reflects the growing complexity of networks and the need to cover new charging scenarios, such as those introduced by 5G and network slicing.