Record Number (Elementary File)

Description

In the context of 3GPP specifications, particularly TS 21.905 (Vocabulary) and TS 31.121 (UICC terminal interface, USIM application test specification), a Record Number is an identifier that uniquely identifies a record within an Elementary File (EF). Elementary Files are the basic storage units on a UICC (Universal Integrated Circuit Card) or SIM card, and they can be organized in different structures, including transparent, linear fixed, and cyclic files. The record number is the key used to address a specific record within linear fixed and cyclic EFs.

The UICC file system is hierarchical, consisting of a Master File (MF), Dedicated Files (DFs), and Elementary Files (EFs). EFs contain the actual data used by applications such as the USIM, ISIM, and other 3GPP applications. For EFs with a linear fixed structure, records are numbered sequentially starting from 1, and each record has a fixed length. For cyclic files, records are also numbered, but the file behaves as a ring buffer where new records overwrite the oldest. In both cases, the record number is the mechanism by which the terminal or application reads, writes, or updates a specific record.

Access to records is performed using commands defined in ISO/IEC 7816-4 and adapted by 3GPP. The READ RECORD command, for example, takes a record number as a parameter to retrieve the contents of that record. Similarly, the UPDATE RECORD command uses the record number to specify which record to modify. The record number is therefore fundamental to the interaction between the terminal (e.g., a mobile device) and the UICC, enabling precise and efficient access to subscription data, phonebook entries, SMS storage, and other application-specific information.

Record numbers are also used in test specifications such as TS 31.121, which defines test cases for the USIM application. In this context, the record number is used to verify that the terminal correctly reads and writes records in various EFs. The test cases ensure interoperability and compliance, and the record number is a key parameter in these tests. The definition of 'record number' as 'the number, which identifies a record within an EF' is concise but captures its essential role as an addressing mechanism.

Because the UICC file system and its access methods have been stable for many years, the definition of record number has remained essentially unchanged from Rel-4 through Rel-19. This stability reflects the maturity of the smart card standards and their continued importance in mobile networks, even as new technologies like eSIM and 5G emerge. The record number remains a foundational concept for anyone working with UICC/SIM data structures and terminal interfaces.

Purpose & Motivation

The Record Number exists to provide a standardized way to address individual records within an Elementary File on a UICC or SIM card. Without such an identifier, terminals and applications would have no reliable means to read or update specific pieces of data, such as a particular phonebook entry or an SMS message stored in a linear fixed file. The record number solves this by assigning a unique index to each record, enabling precise and efficient access.

This concept is rooted in the ISO/IEC 7816 series of standards for smart cards, which 3GPP adopted and extended for telecommunications applications. As UICC-based applications grew in complexity — supporting USIM, ISIM, phonebook, SMS, and more — the need for a consistent addressing scheme became critical. The record number provides that consistency, allowing the same access commands to work across different EFs and different card generations.

Historically, the definition has been stable since Rel-4, reflecting the maturity of the underlying file system standards. While newer technologies like eSIM and remote provisioning have emerged, the fundamental structure of EFs and the use of record numbers remain unchanged. The record number thus continues to be a fundamental building block for UICC data management and terminal interoperability.