Policy Counter Status

Description

The Policy Counter Status is a key concept in 3GPP policy and charging control (PCC) architecture, introduced in Release 11. It represents a label whose values are not standardized by 3GPP but are configured jointly between the Online Charging System (OCS) or Charging Function (CHF) and the Policy and Charging Rules Function (PCRF) or Policy Control Function (PCF). The status is associated with a policy counter's value relative to one or more spending limits (thresholds). The number of possible status values for a policy counter is one greater than the number of thresholds associated with that counter, meaning the status values describe the range around the thresholds (e.g., below first threshold, between first and second, above second). This mechanism allows the OCS/CHF to convey information about subscriber spending to the PCRF/PCF, which can then apply appropriate policy decisions, such as changing QoS, blocking services, or redirecting to a top-up page.

The architecture involves several network elements. The OCS (or CHF in 5G) monitors the subscriber's account balance and usage against predefined spending limits. When the usage crosses a threshold, the OCS updates the policy counter status and sends it to the PCRF (or PCF) over the Sy reference point (in 4G) or the N28 reference point (in 5G). The PCRF/PCF uses this status as input to its policy decisions, potentially modifying the PCC rules for the subscriber's session. The policy counter status is not standardized because operators can define their own labels and thresholds based on business needs, providing flexibility. The PCRF/PCF and OCS/CHF must be configured with the same set of policy counter status values and their mappings to thresholds.

The policy counter status is used in the context of spending limit reports and policy counter status reporting. The PCRF/PCF can subscribe to policy counter status changes from the OCS/CHF, and the OCS/CHF will notify the PCRF/PCF when the status changes. This enables real-time policy enforcement based on spending. For example, a subscriber on a prepaid plan might have a policy counter with thresholds at 80% and 100% of their data allowance. The corresponding status values could be 'below_80', 'between_80_and_100', and 'above_100'. When the subscriber crosses 80%, the OCS sends the new status to the PCRF, which might reduce the QoS or apply a different charging rule. When the subscriber exceeds 100%, the PCRF might block data or redirect to a portal.

The concept has evolved with the introduction of 5G. In Release 20, the definition was updated to reflect the 5G architecture, where the CHF (Charging Function) communicates with the PCF (Policy Control Function) instead of OCS to PCRF. The underlying principle remains the same: the CHF provides policy counter status information to the PCF to enable spending-based policy control. The Sy reference point in 4G is replaced by the N28 reference point in 5G, which is based on the Diameter protocol in 4G and the HTTP/2-based SBI (Service Based Interface) in 5G. The policy counter status is carried in the Spending-Limit-Report-Request/Answer and Policy-Counter-Status-Report-Request/Answer messages.

In summary, the Policy Counter Status is a flexible, operator-defined label that bridges charging and policy control, allowing dynamic policy adjustments based on real-time spending. It is a critical enabler for prepaid and quota-based services, ensuring that subscribers receive appropriate treatment as they approach and exceed their spending limits.

Purpose & Motivation

The Policy Counter Status was introduced to solve the problem of integrating online charging with policy control in real-time. Before its introduction, policy decisions were largely static or based on subscription data, without dynamic input from the charging system. This meant that prepaid subscribers could not have their QoS or service access dynamically adjusted based on their remaining balance or usage. The Policy Counter Status provides a standardized mechanism for the OCS/CHF to inform the PCRF/PCF about the subscriber's spending status relative to thresholds, enabling the PCRF/PCF to apply policies that reflect the current spending situation.

The concept addresses the need for flexible, operator-defined thresholds and status labels. Since spending limits and business rules vary widely among operators, 3GPP chose not to standardize the actual values but rather the mechanism to convey them. This allows operators to define their own policy counters, thresholds, and status labels, tailored to their specific offerings. The PCRF/PCF and OCS/CHF are configured with matching definitions, ensuring interoperability within the operator's network.

Furthermore, the Policy Counter Status enables real-time policy enforcement for prepaid and quota-based services. It allows operators to implement tiered services, where the QoS or access level changes as the subscriber consumes their allowance. This enhances the user experience by providing transparent and dynamic service adjustments, and it helps operators manage network resources and revenue. The evolution to 5G maintains this capability while adapting to the new service-based architecture, ensuring that policy and charging remain tightly integrated in next-generation networks.