a) IMSI

• International Mobile Subscriber Identity – a unique identification that is associated with all GSM and UMTS network mobile phones.
• The SIM inside the phone contains it as a 64 bit field.
• Used for acquiring certain details in Home Location Register or Visitor Location Register.
• IMSI is rarely sent for preventing eavesdroppers to identify and track the subscriber on the radio interface.
• It is presented as 15 digit long number, where first 3 digits represent the Mobile Country Code and followed by the Mobile Network Code.
• Remaining digits are mobile station identification number within the customer base network.

b) TMSI

• Temporary Mobile Subscriber Identity for most commonly sent between the mobile and the network.
• TMSI is assigned randomly by VLR to each mobile in the area.
• The TMSI number is local for a specific local area, and need to be updated every time when the mobile moves to a new geographical area.
• Paging a mobile is the key use of the TMSI.
• The communication between the mobile and the base station is known as paging.
• The emphasis of broadcast information is top set up channels for paging.
• Broadcast mechanism is available in every cellular system for distributing broadcast information to a plurality of mobiles.

c) IMEI

• International Mobile Equipment Identity is a number usually unique for identifying GSM, WCDMA and iDEN mobile phones.
• It is generally printed inside the battery compartment of the phone.
• The number can be displayed on the screen by entering *#06# into the keypad on most of the phones.
• A stolen phone can be stopped from accessing the network within the country, by using IMEI number for valid devices.
• Unlike CDMA/MEID’s electronic serial number, the IMEI is only used for identifying the device and has no permanent relation to the subscriber.
• The subscriber is identified by IMSI number, stored on the SIM card, which then can be transferred to any other handset.

d) MS-IDN

• Mobile Subscriber Integrated services Digital Network Number, a unique number identifying a subscription in a GSM / UMTS mobile network.
• It is the telephone number of the SIM card in a mobile phone.
• MSIDN and IMSI are important numbers used to identify a mobile subscriber.
• MSIDN is used for routing the calls to the subscriber, where as IMSI identifies the SIM.
• In the HLR, the IMSI is the key, and MSIDN is the number that is dialled for connecting a call to the mobile phone.