11.113GPPRelease 1999Specification of the Subscriber Identity Module - Mobile Equipment (SIM-ME) InterfaceTS
This clause specifies the EFs for the GSM session defining access conditions, data items and coding. A data item is a part of an EF which represents a complete logical entity, e.g. the alpha tag in a EFADN record.
EFs or data items having an unassigned value, or, which during the GSM session, are cleared by the ME, shall have their bytes set to ‘FF’. After the administrative phase all data items shall have a defined value or have their bytes set to ‘FF’. If a data item is ‘deleted’ during a GSM session by the allocation of a value specified in another GSM TS, then this value shall be used, and the data item is not unassigned; e.g. for a deleted LAI in EFLOCI the last byte takes the value ‘FE’ (TS 04.08  refers).
EFs are mandatory (M) or optional (O). The file size of an optional EF may be zero. All implemented EFs with a file size greater than zero shall contain all mandatory data items. Optional data items may either be filled with ‘F’, or, if located at the end of an EF, need not exist.
When the coding is according to CCITT Recommendation T.50 , bit 8 of every byte shall be set to 0.
For an overview containing all files see figure 8.