Policy and Charging Control

Description

Policy and Charging Control is a 3GPP framework that provides dynamic, subscriber-aware control of packet flows. It combines policy decisions, such as QoS, gating, and routing, with charging decisions, such as charging key selection, service units, and credit control. The framework was introduced in Rel-7 to support IP multimedia and packet data services that required more flexibility than static charging and QoS profiles. It is used in GPRS, IMS, EPC, and 5G system contexts, although the exact network functions and interfaces have evolved.

The core architecture consists of a Policy and Charging Rules Function, a Policy and Charging Enforcement Function, an Application Function, a Subscriber Profile Repository, and charging systems such as the OCS and Charging Collection Function. The PCRF evaluates subscriber information, service requirements, network conditions, and operator policy to create PCC rules. The PCEF is located in a gateway node, such as a GGSN, PDN Gateway, or User Plane Function, and enforces those rules on packet flows. The AF represents the application layer and requests policy and charging treatment for a media session or service. The SPR stores subscriber profiles, and the OCS provides online charging authorization.

PCC works through a set of defined interfaces. In legacy releases, the Gx interface connects the PCRF and PCEF, the Rx interface connects the AF and PCRF, the Sy interface connects the PCRF and OCS, the S9 interface supports inter-operator policy exchange, and the Sh interface connects the PCRF to the SPR. When an AF requests resources, the PCRF composes rules that identify service data flows, assign QoS parameters, select charging keys, and determine gating behavior. The PCRF sends these rules to the PCEF, which installs packet filters, sets QoS bearers, and opens or closes gating. Usage reports and events from the PCEF are sent to charging nodes, which may trigger reauthorization, balance updates, or policy changes.

The PCC rule itself is a logical object that contains filters, QoS parameters, charging identifiers, gating status, and event triggers. The PCEF may report events such as usage report, service change, or validity time expiry to the PCRF. The PCRF can then modify the rule, request new credit, or instruct the gateway to change QoS or terminate the flow. This event-driven model allows policy and charging to react while a session is active rather than only at session setup.

The framework matters because it decouples service logic from transport enforcement. Before PCC, charging and QoS were largely static and tied to bearer profiles or subscription plans, making it difficult to support real-time applications, video, voice over IP, content charging, and differentiated service tiers. PCC enables operators to apply per-flow policies, react to subscriber balance changes, and coordinate application requirements with network resources. It also supports event reporting, roaming policy exchange, and interworking between different administrative domains.

In 5G, the PCC concept is implemented primarily through the Policy Control Function, Session Management Function, User Plane Function, Application Function, and charging functions using service-based interfaces. The same principles remain: policy rules are generated centrally, enforced at the user plane, and coupled to charging decisions. The glossary definition of PCC refers to this overall policy and charging control framework rather than a single physical node.

Purpose & Motivation

PCC was created because static bearer-based charging and QoS could not meet the needs of IP multimedia, packet data, and differentiated services. In earlier architectures, QoS profiles and charging rules were largely fixed by subscription or bearer type. This made it difficult to support dynamic applications such as voice over IP, video streaming, gaming, and content charging, where the required treatment depends on the active session, subscriber balance, and network conditions.

Rel-7 introduced PCC to provide a common framework for policy and charging control. It separated policy decisions from enforcement, allowing an Application Function to request resources, a PCRF to decide the treatment, and a PCEF to enforce it in the gateway. It also linked policy to online charging through the OCS, so that credit availability could influence QoS and gating. This addressed limitations such as fragmented service provisioning, lack of real-time subscriber control, and inability to monetize services at the flow level.

The framework was motivated by the need for interoperability and convergence across GPRS, IMS, and later EPC. Operators needed a way to apply consistent rules across access networks, roaming scenarios, and application domains. PCC enabled event-triggered policy changes, dynamic QoS, service data flow detection, and charging key selection. In 5G, the same motivation persists: network slicing, edge computing, and application-aware services require centralized, reusable policy decisions, which are implemented through the PCF and related service-based functions.