Home Policy and Charging Rules Function

Description

The Home Policy and Charging Rules Function (H-PCRF) is a central component within the 4G Evolved Packet Core (EPC) architecture, specifically in the Policy and Charging Control (PCC) framework. It serves as the policy decision point for subscribers who are roaming outside their home network. The H-PCRF resides in the Home Public Land Mobile Network (HPLMN) and interfaces with the Visited PCRF (V-PCRF) in the Visited PLMN (VPLMN) via the S9 reference point. Its primary function is to provide the home operator's policy and charging rules to the visited network, ensuring that subscriber-specific services, Quality of Service (QoS), and charging mechanisms are applied consistently during roaming.

Architecturally, the H-PCRF is part of the PCRF, which is the brain of the PCC system. In roaming scenarios, the PCRF is logically split into V-PCRF and H-PCRF. The V-PCRF interacts with the Policy and Charging Enforcement Function (PCEF) in the visited network's PDN Gateway (P-GW) to enforce policies at the bearer level. When policy decisions require input from the home network—such as for subscriber service profiles, data usage limits, or specific QoS authorizations—the V-PCRF forwards requests to the H-PCRF over the S9 interface. The H-PCRF then makes the final policy decision based on subscriber data retrieved from the Subscription Profile Repository (SPR) or later the User Data Repository (UDR).

The H-PCRF operates using the Diameter protocol over the S9 interface, which is an extension of the Gx interface used for non-roaming PCC. It receives Diameter requests (e.g., CCR - Credit-Control-Request) from the V-PCRF containing information about the UE's IP-CAN (IP Connectivity Access Network) session. The H-PCRF processes these requests against home network policies and subscriber information. It then returns Diameter answers (e.g., CCA - Credit-Control-Answer) with Policy and Charging Control (PCC) rules. These rules include parameters for QoS (QCI, ARP, bitrates), gating control (allow/block), and charging instructions (online via OCS, offline via OFCS). The V-PCRF propagates these rules to the PCEF for enforcement.

Key components interfacing with the H-PCRF include the S9 reference point for V-PCRF communication, the Sp/UD reference point for accessing subscriber data from SPR/UDR, and potentially the Rx interface for receiving service information from Application Functions (AFs). Its role is crucial for enabling advanced services like sponsored data, tiered QoS, and roaming packet filters. By centralizing home network policy logic, the H-PCRF allows visited networks to implement policies without needing full subscriber details, simplifying inter-operator agreements and ensuring compliance with home operator business models.

Purpose & Motivation

The H-PCRF was introduced in 3GPP Release 8 as part of the new Policy and Charging Control (PCC) architecture for the Evolved Packet Core (EPC). It was created to address the limitations of earlier policy control mechanisms in 2G/3G networks, which were less flexible and often tied to specific access technologies. Prior to PCC, policy and charging were handled separately with limited dynamic control, making it difficult to implement sophisticated service differentiation and real-time charging for roaming users.

The primary motivation for the H-PCRF was to enable dynamic, subscriber-aware policy and charging control in roaming scenarios. As LTE deployments expanded globally, operators needed a standardized way to enforce home network policies—such as fair usage, service prioritization, and roaming agreements—when subscribers attached to visited networks. The H-PCRF, via the S9 interface, provided a standardized protocol (Diameter) and procedure for home networks to exert control over QoS and charging, ensuring a consistent user experience and accurate billing across borders.

Furthermore, the H-PCRF solved the problem of scalable policy management for roaming. By separating the home and visited policy functions, it reduced the signaling load on visited networks and protected home subscriber data. It also facilitated the introduction of new services like Application Detection and Control (ADC) and sponsored data access in roaming contexts. The H-PCRF's design was essential for the commercial success of LTE roaming, allowing operators to offer complex service plans and maintain revenue assurance while subscribers were abroad.