Transferred Account Procedure

Description

The Transferred Account Procedure (TAP) is a comprehensive set of specifications that standardizes the transfer of billing and accounting data between telecommunications operators, especially in roaming scenarios. It defines the format, content, and procedural rules for creating and exchanging Transferred Account Data (TAD) files, which contain Call Detail Records (CDRs) or other service usage records. The primary objective is to enable the visited network operator (where the roaming subscriber uses services) to send usage records to the home network operator (the subscriber's provider) for billing and settlement purposes. TAP encompasses the entire lifecycle from CDR generation in the visited network to validation, formatting, transmission, and processing in the home network.

Architecturally, TAP involves several key components: the TAP Generating System (typically in the visited network), which creates TAP files from raw CDRs; the TAP File, a structured data container (originally in a binary format, later evolving to XML) that includes header, transfer batch, and trailer records; and the TAP Processing System (in the home network), which receives, validates, and reconciles the files. The procedure specifies detailed rules for data fields such as call type, duration, destination, timestamps, and roaming partner identifiers. It also includes mechanisms for error handling, re-send requests, and acknowledgments to ensure data integrity and completeness. TAP files are usually transferred via secure protocols like FTP or more modern IP-based methods.

In operation, when a roaming subscriber makes a call, sends an SMS, or uses data, the visited network's network elements generate raw CDRs. These are processed by the TAP Generating System, which aggregates them, applies formatting rules, and packages them into TAP files, often on a daily or batch basis. The files are then transmitted to the home operator's TAP Processing System. The home operator validates the files against TAP standards, checks for discrepancies, and uses the data to generate invoices for the roaming subscriber and to calculate inter-operator charges. TAP also supports adjustments, corrections, and dispute resolution through supplementary procedures like RAP (Returned Account Procedure) for rejected records. Its structured approach ensures that operators can accurately settle accounts despite differences in their internal billing systems.

Purpose & Motivation

TAP was created to solve the critical problem of billing and settlement between different mobile network operators in roaming scenarios. Before its standardization, operators used bilateral agreements and proprietary formats to exchange usage data, leading to inconsistencies, errors, and lengthy reconciliation processes. This resulted in revenue leakage, disputes, and inefficiencies, especially as global roaming expanded in the 1990s. The GSM Association (GSMA) recognized the need for a uniform procedure to facilitate seamless roaming and accurate financial settlements, driving the development of TAP as part of the broader GSM standards.

Historically, TAP was first introduced in 3GPP Release 4, building on earlier GSM billing concepts. It addressed the limitations of previous ad-hoc methods by providing a common 'language' for accounting data exchange, enabling automation and reducing manual intervention. The procedure was motivated by the rapid growth of international mobile roaming, where subscribers expect to use services abroad without billing complexities. TAP ensures that visited operators are compensated for providing services to roaming subscribers, while home operators can accurately bill their customers based on standardized records.

Over time, TAP has evolved to support new services like GPRS data, MMS, and LTE roaming, adapting to technological advancements. It solves ongoing challenges in revenue assurance, fraud detection, and regulatory compliance by providing a traceable, auditable process. The creation of TAP was pivotal for the commercial success of global mobile communications, as it established trust and efficiency in inter-operator financial transactions, enabling the widespread adoption of roaming services that users take for granted today.

Key Features

• Standardized format for exchanging billing records (CDRs) between operators
• Supports voice, SMS, data, and value-added service roaming scenarios
• Defines procedures for file generation, transmission, validation, and error handling
• Includes mechanisms for adjustments and dispute resolution (e.g., RAP)
• Enables automated inter-operator settlement and revenue assurance
• Evolves to incorporate new technologies and service types across 3GPP releases

Evolution Across Releases

Defining Specifications