TDF generated Charging Data Record

Description

The TDF generated Charging Data Record (TDF-CDR) is a specific type of CDR used in 3GPP offline charging systems. It is produced by the Traffic Detection Function (TDF) or its charging trigger function (CTF) to record usage information related to the detection and potential control of specific applications. Unlike standard bearer-level CDRs (e.g., S-CDR, G-CDR) that record volume and duration per IP-CAN bearer, the TDF-CDR provides granular, application-aware charging information. It logs events such as the start and stop of an application flow, the specific application or service detected (identified by an Application Identifier), and the volume of data transmitted for that application during the detection period.

The generation of a TDF-CDR is triggered by specific events defined in the Application Detection and Control (ADC) rules provided by the PCRF. These rules can instruct the TDF to generate a CDR when an application session starts, stops, or at periodic intervals. The TDF's Charging Trigger Function collects relevant charging information, formats it according to the 3GPP specification (TS 32.251), and forwards it to the Charging Data Function (CDF) via the Rf or Nchf (in 5G) reference point using the Diameter protocol. The TDF-CDR contains a rich set of fields including the subscriber's identity (e.g., IMSI, MSISDN), the TDF address, the detection time, the application identifier, the reported data volumes (uplink and downlink), and potentially the applied QoS and charging characteristics.

Within the broader charging architecture, TDF-CDRs serve as a crucial input for billing and accounting systems. They enable operators to implement sophisticated charging models based on application usage. For example, an operator can offer a "social media pack" where data used by Facebook and Twitter is zero-rated (not charged), while other data is counted against a monthly allowance. The billing system correlates the TDF-CDRs with other CDRs (like S-CDRs) using a common Charging ID to build a complete picture of a subscriber's session. The TDF-CDR is a key enabler for service differentiation, allowing operators to move beyond flat-rate billing to create value-added, application-specific tariff plans and to provide detailed usage breakdowns to customers.

Purpose & Motivation

The TDF-CDR was standardized in 3GPP Release 12 to address a critical gap in charging capabilities: the inability to charge based on the specific application or service being used. Prior to its introduction, charging systems primarily relied on bearer-level CDRs, which only provided information about total data volume per IP connection (APN). This was sufficient for simple volume-based or time-based charging but inadequate for the growing market of application-based service offerings. Operators wanted to create innovative data plans like "video streaming passes" or "music service bundles," but lacked a standardized mechanism to measure and record application-specific consumption.

The creation of the TDF-CDR solved this problem by providing a standardized, interoperable format for reporting application-level usage from the TDF to the offline charging system. It enabled new business models and charging scenarios that were previously impossible or required proprietary, non-integrated solutions. For instance, it allows for accurate implementation of "sponsored data," where a third-party application provider pays for the data used by their service, as the TDF-CDR clearly identifies the application and its data consumption.

Furthermore, the TDF-CDR supports regulatory compliance and transparency. It provides an auditable record of what applications were used, which can be important for billing disputes or for complying with regulations requiring clear communication of data usage. It also enables detailed analytics for marketing and network planning, as operators can analyze trends in application popularity and consumption patterns. The standardization of TDF-CDR ensured that all network vendors and billing system providers could interoperate, reducing complexity for operators and fostering a competitive ecosystem for application-aware charging solutions.