Visited Charging Function

Description

The Visited Charging Function (V-CHF) is a core network element specified within the 5G System (5GS) architecture to manage charging operations for User Equipment (UE) that are roaming outside their home network. It resides in the Visited Public Land Mobile Network (VPLMN) and works in conjunction with the Home Charging Function (H-CHF) located in the Home Public Land Mobile Network (HPLMN). The primary architectural role of the V-CHF is to act as a charging gateway within the visited network, collecting usage data and forwarding it to the H-CHF for centralized billing and policy decision-making.

Operationally, the V-CHF interfaces with the Session Management Function (SMF) in the VPLMN via the N40 reference point. When a roaming session is established, the SMF interacts with the V-CHF to report charging events based on the subscriber's data usage, service consumption, or specific network events. The V-CHF applies local charging policies, which may be derived from the home network, to generate Charging Data Records (CDRs) or forward charging events in real-time. It utilizes the Nchf interface (specifically Nchf_ConvergedCharging) to communicate with the H-CHF, ensuring that all charging information is securely relayed to the home operator's billing system.

Key components of the V-CHF's functionality include its ability to support both offline and online charging models. In online charging, it can request and manage quota allocations from the H-CHF in real-time to control service usage. Its role is pivotal in enabling seamless roaming experiences by ensuring that charging is accurate, compliant with inter-operator agreements, and does not introduce latency that degrades user experience. The V-CHF is a fundamental part of the 5G charging architecture, decoupling visited network charging actions from the home network's final billing authority.

Purpose & Motivation

The V-CHF was introduced to address the complexities of charging in 5G roaming scenarios, where services are delivered by a visited network but billed by the home network. Prior to its standardization, roaming charging often relied on simpler, less real-time mechanisms that could lead to billing inaccuracies, fraud, or limited support for new service models like network slicing and edge computing. The separation of charging functions between visited and home networks allows for more granular and immediate control over resource usage.

Its creation was motivated by the need for a standardized, interoperable interface for converged charging across network boundaries, as defined in 3GPP Release 16. This enables operators to implement advanced charging policies for roaming subscribers, including support for service-based architecture (SBA) and seamless integration with policy control. The V-CHF solves the problem of how to efficiently and securely report usage data from the visited network to the home network's billing systems without requiring direct integration between every network element, thereby simplifying the charging architecture for roaming.