Charging control

Description

Charging control is a critical function within the 3GPP Policy and Charging Control (PCC) architecture, responsible for applying charging rules to service data flows (SDFs). It involves associating packets belonging to an SDF with a charging key and determining whether to apply online charging, offline charging, or both. This enables operators to charge differently based on the type of service, QoS, or subscriber profile. Charging control is defined in 3GPP TS 23.203 (PCC architecture) and TS 23.503 (5G PCC), and it is enforced by the Policy and Charging Enforcement Function (PCEF) or the Session Management Function (SMF) in 5G.

The process begins when a service data flow is established. The Policy and Charging Rules Function (PCRF) in 4G or the Policy Control Function (PCF) in 5G provides charging rules to the PCEF/SMF. These rules include the charging key (also known as the rating group), which identifies the tariff to be applied. The PCEF/SMF then associates packets of the SDF with this charging key and applies the appropriate charging mode. For online charging, the PCEF/SMF interacts with the Online Charging System (OCS) to request credit authorization before allowing the packets to pass. For offline charging, it generates charging data records (CDRs) that are later processed by the billing domain.

Charging control allows for granular charging based on factors such as QoS class, application, time of day, or subscriber tier. For example, a video streaming service might be charged at a different rate than web browsing. The charging key is used to group flows that share the same charging characteristics, simplifying the charging process. The PCEF/SMF enforces the charging rules by monitoring the traffic and applying the appropriate charging actions. If online charging is used, the OCS may grant a quota of units (e.g., bytes or seconds) that the PCEF/SMF enforces; once the quota is exhausted, the PCEF/SMF must request more credit or terminate the service.

In 5G, charging control is integrated into the Session Management Function (SMF) and the Charging Function (CHF). The PCF provides charging control policies to the SMF, which then enforces them. The SMF uses the Nchf interface to communicate with the CHF for online charging and offline charging data collection. The 5G charging architecture supports converged charging, where online and offline charging can be applied simultaneously for the same session. This flexibility is essential for new 5G services like network slicing and edge computing, where charging may depend on slice identity or edge application.

Charging control is also closely linked to QoS control. The PCC architecture ensures that charging and QoS policies are consistent, so that high-priority traffic can be charged accordingly. For instance, a guaranteed bit rate (GBR) bearer might have a higher charging rate than a non-GBR bearer. The charging key is often derived from the QoS Class Identifier (QCI) or 5G QoS Identifier (5QI), but it can also be based on other parameters like the application identifier or the subscriber's spending limit.

Overall, charging control is a fundamental enabler for flexible and fair charging in mobile networks. It allows operators to monetize services effectively, prevent fraud, and offer personalized pricing. Its evolution from 4G to 5G reflects the increasing complexity and diversity of mobile services, and it continues to be a key area of innovation in 3GPP standards.

Purpose & Motivation

Charging control exists to provide a standardized mechanism for applying charging rules to individual service data flows in a mobile network. Before its introduction, charging was often based on aggregate usage per bearer or APN, which lacked granularity and could not differentiate between different types of traffic within the same bearer. This made it difficult for operators to offer differentiated pricing for specific applications or services, such as charging differently for VoIP versus file downloads.

The introduction of Policy and Charging Control (PCC) in 3GPP Release 7 addressed this by allowing the network to classify traffic into service data flows and apply specific charging and QoS policies to each. Charging control, as part of PCC, enables operators to charge based on the actual service being used, not just the amount of data. This supports business models like zero-rating, sponsored data, and tiered pricing. It also enables real-time credit control for pre-paid subscribers at the service level, preventing revenue loss.

In 5G, charging control has become even more important due to the diverse requirements of enhanced mobile broadband (eMBB), massive machine-type communication (mMTC), and ultra-reliable low-latency communication (URLLC). Each of these may require different charging schemes, and charging control provides the flexibility to implement them. Thus, charging control is essential for operators to remain competitive and innovative in a rapidly evolving market.