Chargeable DURation

Description

Chargeable DURation (CDUR) is a core charging parameter defined within the 3GPP charging architecture, specifically in the context of offline and online charging systems (OFCS and OCS). It quantifies the elapsed time of a service usage event that is subject to charging. The CDUR is not a standalone entity but a critical data element populated within Charging Data Records (CDRs) or credit control messages. Its value is measured in appropriate time units (e.g., seconds, milliseconds) as defined by the relevant tariff.

Architecturally, the CDUR is generated by the network function responsible for monitoring the service event, typically a Call Session Control Function (CSCF) for IMS services, a Serving GPRS Support Node (SGSN) or Gateway GPRS Support Node (GGSN)/Packet Data Network Gateway (PGW) for packet data, or a Mobile Switching Center (MSC) for circuit-switched calls. These Charging Trigger Functions (CTFs) detect the start and stop of a chargeable event. The CTF timestamps these events and calculates the difference, resulting in the CDUR. This duration is then included in the charging information sent to the Charging Data Function (CDF) for offline charging or used in real-time credit deduction with the Online Charging System (OCF).

The technical implementation involves precise time synchronization across network elements to ensure accuracy. The CDUR calculation must account for the specific charging model; for example, it may represent the entire session duration, the duration of a specific media component within an IMS session, or the duration after the first initial time interval in a multi-tiered tariff structure. In online charging, the CDUR is crucial for session-based charging, where the OCS grants a quota of time units. The CTF reports back the consumed CDUR, allowing the OCS to deduct credit and potentially re-authorize further service. The granularity and reporting of CDUR can be configured based on operator policy and the required billing precision.

Its role extends beyond simple billing. CDUR is a key input for revenue assurance, service analytics, and fraud detection systems. Discrepancies in reported CDUR across different network interfaces can indicate faults or fraudulent activity. Furthermore, in the context of QoS-aware charging, different CDUR values might be applied for different bearer quality levels. The parameter's definition in 3GPP specifications ensures interoperability between network equipment and billing systems from different vendors, forming a standardized foundation for time-based service monetization.

Purpose & Motivation

CDUR exists to provide a standardized, accurate, and reliable measure of service consumption time for billing purposes in telecommunications networks. Prior to standardized charging parameters, operators relied on proprietary methods for timing calls and sessions, which created interoperability challenges when integrating multi-vendor networks and billing systems. This lack of standardization could lead to billing errors, revenue leakage, and complex settlement processes between operators. CDUR, as part of the 3GPP charging framework, solves this by defining a universal parameter for representing time-based usage.

The creation of CDUR was motivated by the shift from simple circuit-switched voice billing to more complex charging models for data and multimedia services introduced with 2.5G and 3G networks. As services evolved, so did the need for precise measurement of session duration for new tariff plans, including split billing, time-of-day rates, and service-specific durations (e.g., video call time vs. voice call time). CDUR provides the fundamental building block upon which these complex tariff structures are implemented within the network's charging subsystems.

It addresses the limitation of having charging logic embedded inflexibly within switching equipment. By externalizing the duration as a clear parameter in standardized charging messages (like Diameter Credit-Control or accounting requests), CDUR enables flexible billing systems to apply diverse rate plans without requiring network hardware upgrades. This separation of charging information generation from billing policy application is a cornerstone of modern telecom operations, supporting everything from prepaid mobile plans to enterprise VoIP billing.