Predefined PCC Rule

Description

A Predefined PCC Rule is a Policy and Charging Control (PCC) rule that has been provisioned directly into the Session Management Function (SMF) by the operator. It is defined in 3GPP TS 23.503 (Policy and Charging Control Framework for the 5G System) and TS 29.512 (Session Management Policy Control Service). Unlike dynamic PCC rules, which are generated by the Policy Control Function (PCF) and signaled to the SMF during session establishment or modification, Predefined PCC Rules are statically configured in the SMF and are activated when certain conditions are met — for example, when a UE requests a specific service or when a session is established with a particular DNN (Data Network Name) or S-NSSAI (Single Network Slice Selection Assistance Information).

In the 5G PCC architecture, the PCF is the central policy decision point. It typically provides PCC rules to the SMF over the N7 interface using the Npcf_SMPolicyControl service. However, there are scenarios where the PCF may not be involved, or where the operator wants to ensure that certain policies are always available even if the PCF is unreachable or if the session is established without PCF interaction. Predefined PCC Rules address this need by embedding policy directly in the SMF. The SMF can then apply these rules locally, without waiting for a policy decision from the PCF. This is particularly useful for basic connectivity, emergency services, or operator-specific default policies.

The activation of a Predefined PCC Rule can be triggered by several mechanisms. The PCF may, during a policy session, reference a predefined rule by its identifier (PCC rule ID) and instruct the SMF to activate it. Alternatively, the SMF may activate predefined rules based on local configuration when no PCF is involved, such as during initial registration or when a PDU session is established without dynamic policy control. The rule itself contains the same components as a dynamic PCC rule: a rule identifier, service data flow (SDF) templates that define the traffic to which the rule applies, QoS parameters (5QI, ARP, GBR/MBR, etc.), and charging parameters (charging key, charging method, measurement method, etc.). Once activated, the rule is enforced by the SMF and the UPF (User Plane Function) in the same way as a dynamic rule.

Predefined PCC Rules are especially important in roaming scenarios and in deployments where the PCF is centralized while SMFs are distributed. They allow the operator to define a baseline set of policies that are always available at the SMF, reducing signaling load and improving resilience. They also simplify the configuration of default bearers or QoS flows for specific services. For example, an operator might define a Predefined PCC Rule for IMS signaling that ensures it always receives the appropriate QoS treatment, even if the PCF is temporarily unavailable. Similarly, a Predefined PCC Rule could be used for emergency services to guarantee priority handling.

The concept was introduced in Release 16 as part of the ongoing evolution of the 5G PCC framework. It builds on the earlier concept of predefined rules in the EPC (Evolved Packet Core) PCC architecture, where they were known as 'predefined PCC rules' or 'preconfigured rules' and were provisioned in the PCRF or PCEF. In 5G, the SMF takes on the role of the PCEF for session management, and the Predefined PCC Rule is the equivalent mechanism. The definition has remained stable from Rel-16 through Rel-20, indicating that the concept is well-established and continues to serve its purpose in 5G and beyond.

Purpose & Motivation

Predefined PCC Rules exist to provide a resilient, operator-controlled baseline for policy and charging enforcement that does not depend on real-time interaction with the PCF. In the 5G Service-Based Architecture (SBA), the PCF is a centralized network function that makes policy decisions for PDU sessions. However, there are situations where the PCF may not be reachable, where the operator wants to minimize signaling, or where a session must be established with a guaranteed set of policies regardless of dynamic conditions. Predefined PCC Rules solve this by allowing the operator to provision rules directly into the SMF, ensuring that essential policies are always available locally.

Historically, the concept of predefined rules originated in the EPC PCC architecture defined in 3GPP TS 23.203, where the PCRF could provision predefined rules in the PCEF. These rules were used for default bearers, emergency services, and operator-specific policies. When 5G introduced the SMF and the new PCC framework in TS 23.503, the concept was adapted and formalized as the Predefined PCC Rule. The need for this adaptation arose from the more distributed nature of the 5G core: SMFs can be deployed at the edge, and requiring every session to consult a centralized PCF for basic policies would introduce latency and single points of failure. Predefined PCC Rules allow the SMF to act autonomously for well-known policy scenarios.

The Predefined PCC Rule also supports network slicing and differentiated services. Operators can define different sets of predefined rules for different S-NSSAIs or DNNs, ensuring that each slice or service gets the appropriate QoS and charging treatment from the moment a session is established. This is particularly valuable for mission-critical services, IoT deployments, and enterprise use cases where consistent policy enforcement is essential. By providing a standardized way to embed policy in the SMF, 3GPP ensures multi-vendor interoperability and gives operators fine-grained control over their policy framework without sacrificing flexibility or resilience.