IMSI = International Mobile Subscriber Identity

TMSI = Temporary Mobile Subscriber Identity

IMEI = International Mobile Equipment Identity

MS-ISDN =Mobile Station ISDN Number

• The MSISDN is the directory number allocated to the mobile subscriber. It is dialed to make a telephone call to the mobile subscriber.
• A MS is identified by its IMSI. The IMSI is embodied in the SIM of the mobile equipment. It is provided by the MS anytime it accesses the NETWORK.
• The TMSI is an identity alias which is used instead of the IMSI when POSSIBLE. The use of a TMSI ensures that the true identity of the mobile subscriber remains confidential by eliminating the need to transfer an IMSI code unciphered over a radio link.
• A VLR allocates a unique TMSI code to each mobile subscriber that is operating in its area. This code, which is only valid within the area supervised by the VLR, is used to identify the subscriber in messages to and from the MS.
• When a CHANGE of location area also involves a change of VLR area, a new TMSI code is allocated and COMMUNICATED to the MS. The MS stores the TMSI on its SIM.
• IMEI codes that identify the mobile equipment deployed in the GSM system.

IMSI = International Mobile Subscriber Identity

TMSI = Temporary Mobile Subscriber Identity

IMEI = International Mobile Equipment Identity

MS-ISDN =Mobile Station ISDN Number