Policy and Charging Control Decision

Description

The PCC decision is a central concept in 3GPP's Policy and Charging Control (PCC) architecture. It represents the output of policy decision-making by the Policy Control Function (PCF) in 5G or the Policy and Charging Rules Function (PCRF) in earlier generations. A PCC decision encompasses a set of rules and parameters that dictate how a service data flow should be handled with respect to policy control (e.g., QoS, gating) and charging control (e.g., online/offline charging). The decision is communicated to enforcement functions such as the Session Management Function (SMF) in 5G or the Policy and Charging Enforcement Function (PCEF) in 4G, which then apply the rules to the user plane traffic.

In the 5G System (5GS), the PCC decision is more granular and can be targeted to different consumers. The PCF can provide a PCC decision for policy and charging control to the SMF, consisting of PCC rules and PDU Session related attributes. It can also provide a decision for access and mobility related control to the AMF, a decision for UE access selection and PDU Session selection related policy to the UE, and a decision for background data transfer policy to the Application Function (AF). This multi-target approach reflects the expanded role of policy in 5G, covering not just session-level QoS but also mobility, UE route selection, and application-specific policies.

The PCC decision is constructed based on various inputs: subscription information from the UDR, application requirements from the AF, network conditions, and operator policies. The PCF evaluates these inputs and generates PCC rules, which are the building blocks of the decision. Each PCC rule contains information such as service data flow filters (to identify the traffic), QoS parameters (e.g., 5QI, ARP, MBR, GBR), charging parameters (e.g., charging key, metering method), and other control information. The decision may also include PDU Session related attributes like the authorized QoS for the session, and for the AMF, access and mobility related policies such as RFSP index or service area restrictions.

Once the PCC decision is made, it is transmitted to the enforcement functions via the appropriate interfaces: N7 (PCF-SMF), N15 (PCF-AMF), N1 (PCF-UE via AMF), and N5 (PCF-AF). The SMF then installs the PCC rules into the UPF, which enforces them on the user plane traffic. The AMF uses the access and mobility policy to control UE registration and mobility. The UE uses the UE policy for access selection and PDU Session establishment. The AF receives background data transfer policies to schedule data transfers. This distributed enforcement ensures that policy decisions are applied consistently across the network.

The PCC decision concept has evolved significantly from its introduction in Release 7. Initially, it was a simple set of PCC rules and IP-CAN bearer attributes provided by the PCRF to the PCEF. Over time, it expanded to include application detection and control (ADC) in Release 11, and with the advent of 5G in Release 16, it was redefined to cover multiple decision types for different network functions. This evolution mirrors the growing complexity of mobile networks and the need for flexible, fine-grained policy control across multiple domains.

Purpose & Motivation

The PCC decision exists to centralize and standardize policy and charging control in mobile networks. Before its introduction, policy control and charging were often handled by separate, proprietary mechanisms, leading to inconsistent enforcement and limited flexibility. The PCC architecture, introduced in Release 7, aimed to unify these functions under a single policy framework, enabling operators to dynamically control QoS, charging, and access based on application requirements and subscriber profiles.

The PCC decision solves the problem of how to translate high-level policy intentions into enforceable rules at the network edge. It provides a structured way for the policy controller (PCRF/PCF) to communicate with enforcement points (PCEF/SMF/UPF) and other consumers (AMF, UE, AF). This separation of decision and enforcement allows for centralized policy management while maintaining distributed enforcement, which is essential for scalability and performance.

Historically, the PCC decision was initially focused on IP-CAN bearer attributes and PCC rules for the PCEF. As networks evolved to 5G, the decision expanded to cover access and mobility, UE policy, and application-specific policies. This reflects the broader role of policy in 5G, where it must support diverse services like URLLC, eMBB, and mMTC, each with different QoS and charging requirements. The PCC decision thus remains a cornerstone of the 5G policy framework, enabling operators to monetize and manage their networks effectively.