Visited Policy Control Function

Description

The Visited Policy Control Function (V-PCF) is a fundamental component of the 5G Core (5GC) network architecture, specifically designed for handling policy control in roaming scenarios. When a User Equipment (UE) attaches to a 5G network outside its home operator's coverage (the Visited PLMN), the V-PCF in that visited network becomes responsible for policy decisions related to that roaming session. It is part of the visited network's Control Plane Function (CPF) set. The V-PCF interfaces with several key network functions. Crucially, it communicates with the Home PCF (H-PCF) in the subscriber's home network via the N24 reference point, a service-based interface. Through this interface, the V-PCF can retrieve subscriber-specific policy information, such as allowed network slice selections, subscribed QoS profiles, and spending limits. The V-PCF also interfaces with other visited network functions like the Access and Mobility Management Function (V-AMF) via the N15 interface for access and mobility-related policies, and with the Session Management Function (V-SMF) via the N7 interface for session management policies (PCC rules). The V-PCF acts as a policy decision point (PDP), translating the high-level service requirements from the H-PCF and network triggers into concrete policy rules. These rules govern aspects such as which network slice instance the UE can access, the QoS parameters for its Protocol Data Unit (PDU) sessions, and policies related to charging and traffic steering. The V-PCF then pushes these decisions to the relevant enforcement functions (like the V-SMF) within the visited network. This architecture ensures that the home operator's policy framework is consistently applied even when the subscriber's traffic is routed through a foreign network's user plane functions.

Purpose & Motivation

The V-PCF was introduced with the 5G System (5GS) in 3GPP Release 15 to provide a modern, service-based, and flexible policy control framework for roaming, superseding the earlier PCRF-based architecture used in 4G. The 5G system introduced new complexities like network slicing, diverse service requirements (eMBB, URLLC, mMTC), and a service-based architecture (SBA). A simple extension of the legacy V-PCRF concept was insufficient. The V-PCF was designed to be the central policy arbiter in the visited network, capable of handling policy decisions for these new 5G paradigms. It solves the problem of applying granular, slice-aware, and service-specific policies from the home network within the infrastructure of a different operator. By having a dedicated policy function in the visited domain that communicates seamlessly with the home domain, it enables advanced roaming features like seamless access to specific network slices, consistent application of QoS policies for mission-critical services, and support for edge computing scenarios in visited locations. It provides the necessary control plane separation and flexibility required for 5G's diverse use cases while maintaining operator autonomy and commercial agreements between home and visited networks.