Access Class

It is not intended that access control be used under normal operating conditions.
The use of this facility allows the network operator to prevent overload of the access channel under critical conditions.

Under certain circumstances, it will be desirable to prevent UE users from making access attempts (including emergency call attempts) or responding to pages in specified areas of a PLMN. Such situations may arise during states of emergency, or where 1 of 2 or more co-located PLMNs has failed.

All UE's are member of one out of 10 access class - given randomly (0 to 9).
The population number is stored in the SIM/USIM.In addition, mobiles may be members of one or more out of 5 special categories (Access Classes 11 to 15), also held in the SIM/USIM.
These are allocated to specific high priority users as follows. (The enumeration is not meant as a priority sequence):

Class 15 - PLMN Staff;
-"- 14 - Emergency Services;
-"- 13 - Public Utilities (e.g. water/gas suppliers);
-"- 12 - Security Services;
-"- 11 - For PLMN Use.


EF_ACC 6F78 is the location in sim card for access class.
This is 2 byte.

Example:
Bellow specified  entry tells that sim card has only 15 as a Access Class (Which is wrong)
EF_ACC (6F78) to 0x80 (Byte 1), 0x00 (Byte 2) - only class 15 bit is set

Bellow specified  entry tells that sim card has 15 and 0 as  Access Class (Which is correct)
EF_ACC (6F78) to 0x80 (Byte 1), 0x01 (Byte 2) - class 15 and class 0 bit is set

link: http://www.qtc.jp/3GPP/Specs/22011-940.pdf