Policy and Charging Control Rule

Description

The PCC rule is the atomic unit of policy and charging control in 3GPP networks. Defined in specifications such as 23.203, 23.503, 29.214, 29.512, and 29.514, it encapsulates all the information needed to detect a service data flow and apply policy and charging treatment to it. A PCC rule is generated by the Policy Control Function (PCF) in 5G or the Policy and Charging Rules Function (PCRF) in 4G, and is enforced by the Session Management Function (SMF) and User Plane Function (UPF) in 5G, or the Policy and Charging Enforcement Function (PCEF) in 4G. The rule contains a service data flow filter (or template) that identifies the packets belonging to the flow, along with parameters for QoS control, charging, and other policies.

The structure of a PCC rule is detailed in clause 6.3.1 of the relevant specifications. It includes several key components: the rule identifier, the service data flow detection information (e.g., IP 5-tuple, application identifier), the charging parameters (e.g., charging key, charging method, measurement method), the policy control parameters (e.g., QoS class identifier, allocation and retention priority, bit rates), and possibly other control information such as gating, redirect, or application detection and control instructions. The rule may also include a precedence value to resolve conflicts when multiple rules match the same traffic. In 5G, PCC rules are extended to support PDU Session related attributes and can be used for both 3GPP and non-3GPP access.

PCC rules are installed, modified, or removed dynamically based on policy decisions. The PCF may provision rules at PDU Session establishment or modify them during the session in response to application requests, subscription changes, or network conditions. The SMF receives the rules over the N7 interface and translates them into UPF-specific instructions, such as packet detection rules (PDRs), QoS enforcement rules (QERs), and usage reporting rules (URRs). The UPF then enforces these rules on the user plane, ensuring that each service data flow receives the appropriate QoS and charging treatment.

The PCC rule concept has evolved over releases. Initially, in Release 7, it was defined as 'a set of information enabling the detection of a service data flow and providing parameters for policy control and/or charging control.' In Release 11, the definition was expanded to include application detection and control for PCEF enhanced with ADC. In Release 16, the definition was further broadened to include 'other control or support information,' reflecting the growing complexity of policy control in 5G. This evolution shows how the PCC rule has adapted to new requirements, such as application awareness, network slicing, and multi-access edge computing.

In practice, PCC rules are crucial for enabling differentiated services. For example, a rule might prioritize VoIP traffic with a specific 5QI and guaranteed bit rate, while another rule might apply zero-rating for a particular application. The flexibility of PCC rules allows operators to implement complex charging schemes, QoS policies, and traffic steering. They are also used for network slicing, where each slice may have its own set of PCC rules to enforce slice-specific policies. Thus, the PCC rule remains a cornerstone of policy and charging control in modern mobile networks.

Purpose & Motivation

The PCC rule exists to provide a standardized, granular mechanism for controlling policy and charging at the service data flow level. Before its introduction, policy and charging control were often coarse-grained, applied at the bearer or session level, which limited operators' ability to differentiate services and charge accordingly. The PCC rule solves this by enabling the detection of individual service data flows and the application of specific policies to each flow, allowing for fine-grained QoS and charging control.

The motivation for PCC rules came from the need to support diverse applications with different requirements in an all-IP mobile network. Operators wanted to offer tiered services, apply fair usage policies, and enable application-specific charging. The PCC rule provides the necessary abstraction: it defines what traffic to match (via service data flow filters) and what treatment to apply (via QoS and charging parameters). This allows the policy controller to make decisions based on application requirements, subscriber profiles, and network conditions, and to communicate those decisions to enforcement points in a consistent format.

Historically, the PCC rule was introduced in Release 7 as part of the PCC architecture. It was initially focused on IP-CAN bearer attributes and basic policy/charging control. Over time, it was enhanced to support application detection and control (Release 11) and other control or support information (Release 16). These enhancements reflect the evolving needs of mobile networks, such as the ability to detect and control encrypted traffic, and the integration of policy control with other network functions like network slicing and edge computing. The PCC rule thus remains a flexible and powerful tool for operators to manage their networks.