Billing

Description

Billing in 3GPP is a critical business and operational function that transforms charging data collected from the network into bills that subscribers must pay. It is part of the overall charging and billing architecture, which includes charging functions that generate Charging Data Records (CDRs) and billing functions that process these CDRs into invoices. The billing function is located in the billing domain, which is separate from the Core Network (CS domain, PS domain, or IMS) and is typically managed by the operator's Business Support Systems (BSS). The 3GPP specifications for billing are found in the 32.xxx series (e.g., 32.240, 32.250, 32.251, 32.260, 32.270, etc.) and in 22.115, 22.127, 22.924, 23.815, and 21.905.

The billing process begins with charging, where the network elements (e.g., SMF, UPF, AMF, PCF in 5G) collect usage data and generate CDRs. These CDRs contain detailed information about the service usage, such as data volume, duration, QoS, location, and time. The CDRs are then transferred to the charging system, which may be an offline charging system (for post-paid) or an online charging system (for pre-paid). The billing function receives these CDRs (or aggregated charging data) and applies rating and pricing rules to calculate the charges. Rating involves determining the price per unit of usage based on the subscriber's tariff plan, time of day, location, and other factors. The billing function then aggregates the charges over a billing period and generates an invoice.

For pre-paid subscribers, billing involves real-time deduction from an account balance. The online charging system interacts with the network to authorize and charge the usage in real-time, ensuring that the subscriber does not exceed their available balance. The billing function in this case manages the account balance, performs the deduction, and may trigger notifications when the balance is low. For post-paid subscribers, the billing function accumulates charges over a period and issues an invoice, which may include an optional list of detailed charges (itemized bill). The invoice is delivered to the user via various channels (mail, email, online portal).

The billing function is not part of the 3GPP core network domains; it resides in the billing domain, which is outside the scope of the CS, PS, and IMS domains. This separation allows operators to use specialized BSS systems for billing, which can integrate with other business processes such as customer relationship management (CRM), revenue assurance, and fraud management. The 3GPP specifications define the interfaces and protocols for transferring charging data from the network to the billing domain, ensuring interoperability between network equipment and BSS.

In summary, billing is the end-to-end process of converting charging data into payable bills. It encompasses rating, aggregation, invoice generation, and pre-paid account management. It is essential for operators to monetize their services and for subscribers to understand their charges. The 3GPP standards ensure that charging data is accurately and reliably conveyed to the billing domain, enabling flexible and scalable billing solutions for various business models.

Purpose & Motivation

Billing exists to enable operators to charge subscribers for the services they use, which is fundamental to the business model of telecommunications. Without billing, operators cannot generate revenue, and subscribers cannot be billed accurately for their usage. The 3GPP billing architecture was developed to standardize the interfaces and procedures for collecting charging data from the network and processing it into bills. This standardization ensures that network equipment from different vendors can interoperate with billing systems, reducing integration costs and enabling competitive markets.

Historically, billing was relatively simple, with basic voice call charging based on duration. As networks evolved to support data services, value-added services, and complex tariff plans, billing became more sophisticated. The introduction of CDRs and charging functions allowed for detailed usage tracking, but the billing function itself remained outside the core network. The 3GPP specifications define the charging data that network elements must produce and the protocols for transferring it to the billing domain. This separation of concerns allows operators to deploy best-of-breed billing systems and adapt to new business models, such as pre-paid, post-paid, and converged charging.

The billing function also addresses the need for real-time charging in pre-paid scenarios, where subscribers pay in advance and require immediate deduction from their balance. This requires online charging systems that can interact with the network in real-time to authorize and charge usage. The 3GPP standards for online charging (e.g., 32.296, 32.299) define the protocols and procedures for this interaction. Overall, billing is a critical enabler for service monetization, customer satisfaction, and regulatory compliance, and the 3GPP standards ensure it can be implemented efficiently and consistently across different networks and vendors.