Flow Based bearer Charging

Description

Flow Based bearer Charging (FBC) is an architectural framework within the 3GPP Packet Switched (PS) domain that enables charging based on the detection and measurement of individual IP flows or Service Data Flows (SDFs). It moves beyond bearer-level charging (where all traffic on a PDP context is charged uniformly) to a more granular model. The core network nodes, specifically the Gateway GPRS Support Node (GGSN) in GPRS/UMTS or the Packet Data Network Gateway (P-GW) in EPS, are enhanced with Traffic Plane Functionalities that include Deep Packet Inspection (DPI) and flow classification capabilities. These gateways identify individual flows based on packet filters defined by policy rules, typically provided by the Policy and Charging Rules Function (PCRF).

The charging process works by associating each detected SDF with a specific Charging Key. The gateway then measures parameters for that flow, such as volume of data uplink/downlink, duration, or specific events. This usage data is formatted into Charging Data Records (CDRs) or formatted for online charging via the Gy reference point. The records are sent to the Charging Data Function (CDF) for offline charging or to the Online Charging System (OCS) via the Gy interface for real-time credit control. A single bearer (PDP context or EPS bearer) can thus contain multiple, separately charged SDFs. For example, a user's default bearer might carry a basic internet flow charged at one rate, a video streaming flow charged at a premium rate, and a zero-rated messaging app flow.

FBC is integral to the Policy and Charging Control (PCC) architecture defined in 3GPP. The PCRF uses the Sp (or Gx) interface to provision the gateway with Policy and Charging Control (PCC) rules. Each PCC rule contains the flow filters for identifying an SDF, the associated Charging Key, and other charging characteristics (e.g., whether charging is online or offline, rating group). This tight integration allows for dynamic, service-driven charging. The architecture supports both offline and online charging models, enabling prepaid and postpaid billing scenarios with high granularity. FBC is fundamental to implementing sophisticated service plans like tiered data access, sponsored data, and quality-of-service-based billing.

Purpose & Motivation

FBC was introduced to address the limitations of bearer-level charging in the face of evolving mobile data services. Early GPRS/UMTS networks charged based on the aggregate data volume on a PDP context, which treated all internet traffic equally. This model became inadequate as operators launched diverse services like VoIP, video streaming, and partner content, each requiring different billing models (e.g., per-minute, premium data buckets, or content-provider sponsored data). FBC was created to enable service-aware charging.

The primary motivation was to allow operators to monetize network services more flexibly and create new revenue streams. It solved the problem of not being able to distinguish between different types of traffic flowing through the same IP connection for billing purposes. By enabling charging per IP flow, operators could implement differentiated pricing, zero-rating, and service-specific promotions. Furthermore, it provided the technical foundation for coupling charging with quality of service (QoS), allowing operators to charge a premium for guaranteed bit-rate services. FBC, as part of the broader PCC framework, was a key enabler for the transition from simple data access to rich, billable service offerings in 3G and 4G networks, directly supporting business models like two-sided markets where content providers could pay for user data consumption.