May 2006, Issue 190

Mobile Phone Book
M16C/62P-Based Data Backup System
Renesas M16C 2005 Honorable Mention

SIM FILE STRUCTURE

The files, which are organized in a hierarchical structure, may be either administrative or application-specific. The operating system handles access to the data stored in different files.

Files are composed of a header, which the SIM internally manages, and an optional body part. The information about the header, which is related to the structure and attributes of the file, may be obtained with the GET RESPONSE or STATUS commands. This information is fixed during the administrative phase. The body part contains the data of the file.

A file ID is used to address or identify each file. Consisting of two bytes, the file ID is coded in hexadecimal notation. The first byte identifies the type of file. For GSM 3F, it’s the master file. 7F is a dedicated file (DF). 2F is an elementary file under the master file. 6F is an elementary file under a dedicated file.

A dedicated file is a functional grouping of files including the DF and all the files that contain this DF in their parental hierarchy (i.e., it consists of the DF and its complete sub-tree). A DF consists of only a header part.

There are three DFs defined in the GSM specifications. DFGSM contains the application for both GSM and DCS1800. DFIS41 contains the applications for the IS-41 standard as specified by the American National Standards Institute (ANSI) T1P1. DFTELECOM contains telecom service features. All three files, which are immediate children of the master file (MF), may coexist on a multiple-application card.

An elementary file (EF) is composed of a header and a body part. GSM uses three structures of an EF. An EF with a transparent structure consists of a sequence of bytes. When reading or updating, the sequence of bytes to be acted on is referenced by a relative address (offset), which indicates the start position (in bytes) and the number of bytes to be read or updated. The first byte of a transparent EF has the relative address 00 00. The total data length of the body of the EF is indicated in the EF header. Otherwise, an EF with a linear fixed structure consists of a sequence of records all having the same fixed length. The first record is record number 1. The length of a record, as well as this value multiplied by the number of records, is indicated in the EF’s header.

Finally, an EF with a cyclic structure consists of a fixed number of records with the same (fixed) length. In this file structure, there’s a link between the last record (n) and the first record. When the record pointer is set to n, then the next record is record 1. Similarly, when the record pointer is set to record 1, then the previous record is record n. The last updated record containing the newest data is record number 1. The oldest data is held in record number n.

After the ATR, the MF is implicitly selected and it becomes the current directory. You may then select each file with the SELECT function.