When the mobile operator needs to implement ACCOLC restriction, they will update the configuration on the specified cell sites. The access class value is a field that is transmitted in the broadcast channel of the cell. Under normal conditions, access class levels 0 – 15 are allowed. The SIM card compares what is allowed to its own access class level. If the allowed access class levels being broadcast by the cell site does not match what is on the SIM card, then the mobile device cannot access that cell – for any services.