Policy Counter Identifier

Description

The Policy Counter Identifier is a key identifier in 3GPP policy and charging control, introduced in Release 11. It serves as a reference to a specific policy counter within the Online Charging System (OCS) or, in later releases, the Charging Function (CHF) for a given subscriber. The identifier allows the Policy and Charging Rules Function (PCRF) in 4G or the Policy Control Function (PCF) in 5G to uniquely identify and interact with a particular policy counter when making policy decisions based on spending or usage.

In the 3GPP architecture, the Policy Counter Identifier is used in signaling between the PCRF/PCF and the OCS/CHF. When the PCRF/PCF needs to monitor a subscriber's spending against a specific counter, it includes the Policy Counter Identifier in its request to the OCS/CHF. The OCS/CHF uses this identifier to locate the corresponding counter and return its status or subscribe to notifications. The identifier is typically a string or numeric value that is provisioned in the OCS/CHF and known to the PCRF/PCF, often derived from the subscriber's profile or service agreement.

The Policy Counter Identifier is defined in several 3GPP specifications: TS 23.203 (Policy and Charging Control Architecture) for 4G, TS 23.503 (Policy and Charging Control Framework for the 5G System) for 5G, and stage 3 specifications TS 29.219 (Policy and Charging Control: Spending Limit Reporting over Sy reference point) and TS 29.594 (5G System; Spending Limit Control Service). These specifications define the format and usage of the identifier in the respective interfaces (Sy for 4G, N28 for 5G).

How it works: During session establishment or policy decision, the PCRF/PCF determines which policy counters are relevant for the subscriber based on their subscription. It then sends a request to the OCS/CHF containing the Policy Counter Identifier(s). The OCS/CHF responds with the current status of the counter(s) and may set up notifications for threshold crossings. The PCRF/PCF uses this information to apply policy rules, such as blocking or throttling when a spending limit is reached. The identifier ensures that the correct counter is referenced, especially when multiple counters exist for different services or time periods.

The Policy Counter Identifier is essential for enabling personalized and dynamic policy control. It allows operators to define multiple counters per subscriber (e.g., one for data, one for voice, one for roaming) and to apply different policies based on each counter's status. In 5G, the identifier continues to play a crucial role in the converged charging architecture, supporting advanced use cases like network slicing and IoT where differentiated charging and policy are required.

Purpose & Motivation

The Policy Counter Identifier was created to provide a standardized way to reference specific policy counters in the charging system. Without a unique identifier, the PCRF/PCF would not be able to distinguish between multiple counters that might exist for a subscriber, leading to ambiguity and incorrect policy enforcement. The identifier enables precise communication between the policy and charging domains, ensuring that the correct spending or usage data is used for policy decisions.

In earlier implementations, policy control and charging were often tightly coupled or used proprietary identifiers, which limited interoperability and flexibility. The introduction of the Policy Counter Identifier in Release 11 as part of the Sy interface standardized the interaction, allowing multi-vendor deployments and simplifying the integration of policy and charging systems. This was particularly important as operators began to offer more complex service plans and needed to enforce spending limits accurately.

With the evolution to 5G, the Policy Counter Identifier remains vital, now used over the N28 interface with the CHF. The shift from OCS to CHF in Release 20 reflects the convergence of charging functions, but the need for a unique identifier persists. The identifier supports the diverse requirements of 5G, including network slicing, where different slices may have distinct counters and policies, and IoT, where massive numbers of devices require efficient and scalable charging and policy control.