Mobile switching center (MSC)：The mobile switching center (MSC) is the primary service delivery node for GSM/CDMA, responsible for routing voice calls and SMS as well as other services (such as conference calls, FAX and circuit switched data).
The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real time pre-paid account monitoring.
The home location register (HLR) for obtaining data about the SIM and mobile services ISDN number (MSISDN; i.e., the telephone number).
Examples of other data stored in the HLR against an IMSI record is:
The UMTS terrestrial radio access network (UTRAN) which handles the radio communication with 3G mobile phones.
The visitor location register (VLR) for determining where other mobile subscribers are located.
VLR Data stored include: