Authentication center (AUC). 

    * To protect GSM systems, the following security functions have been defined: 

            Subscriber authentication: by performing authentication, the network 

            ensures that no unauthorized users can access the network, including 

            those that are attempting to impersonate others.  

  

            Radio information ciphering: the information sent between the network 

               and a MS is ciphered. A MS can only decipher information intended for it.