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:
- GSM services that the subscriber has requested or been given.
- GPRS settings to allow the subscriber to access packet services.
- Current location of subscriber (VLR and serving GPRS support node/SGSN).
- Call divert settings applicable for each associated MSISDN.
The base station subsystem (BSS) which handles the radio communication with 2G and 2.5G mobile phones.
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:
- IMSI (the subscriber’s identity number).
- Authentication data.
- MSISDN (the subscriber’s phone number).
- GSM services that the subscriber is allowed to access.
- access point (GPRS) subscribed.
- The HLR address of the subscriber.