Visited Policy and Charging Rules Function

Description

The Visited Policy and Charging Rules Function (V-PCRF) is a pivotal network element in the 3GPP Policy and Charging Control (PCC) architecture for EPS (Evolved Packet System) and earlier systems, specifically handling roaming. It resides in the Visited Public Land Mobile Network (VPLMN). Its primary function is to facilitate policy and charging control for a subscriber who is roaming. The V-PCRF does not typically make final policy decisions itself; instead, it acts as an intermediary between the enforcement point in the visited network (the V-PCEF, located at the PGW) and the decision point in the home network (the H-PCRF). The communication between the V-PCRF and the H-PCRF occurs over the S9 reference point, which is a Diameter-based protocol. When a roaming subscriber establishes a PDN connection, the V-PCEF signals to the V-PCRF (via the Gx interface). The V-PCRF then initiates a session with the H-PCRF over S9, forwarding information like the subscriber's identity and the requested service. The H-PCRF, which has access to the subscriber's profile and service data, makes the policy decisions and generates PCC rules. These rules are sent back to the V-PCRF. The V-PCRF may perform local functions such as adding visited network-specific policies (e.g., related to local breakout or visited network charging agreements) or simply forwarding the H-PCRF's rules. Finally, the V-PCRF provisions these PCC rules to the V-PCEF via the Gx interface. The V-PCRF thus serves as the local policy and charging rules function anchor in the visited network, ensuring that the home operator's policies are correctly interpreted and applied within the visited network's context, while also allowing the visited operator to inject its own policy logic where permitted by roaming agreements.

Purpose & Motivation

The V-PCRF was introduced to extend the PCC framework, originally defined for the home network, into robust roaming scenarios. Before standardized PCC roaming, applying dynamic, service-aware policies for roamers was difficult, often leading to a 'lowest common denominator' service experience. The V-PCRF addresses this by establishing a clear architectural split: the home network (H-PCRF) owns the subscriber and makes the primary policy decisions, while the visited network provides a local policy function (V-PCRF) to interface with its own enforcement point (V-PCEF). This model solves several problems. It allows the home operator to maintain control over the subscriber's service experience and charging. It enables the visited operator to manage its own network resources and apply any local policies or charging supplements. It also provides a scalable and secure interface (S9) between operators, hiding internal network details. The V-PCRF is essential for enabling advanced services like IMS roaming, where consistent QoS for voice and video calls is required regardless of location, and for implementing complex charging models like sponsored data connectivity in a roaming context.