International Mobile Subscriber Identity

related topics
{system, computer, user}
{math, number, function}
{country, population, people}
{law, state, case}
{work, book, publish}
{company, market, business}
{language, word, form}
{area, part, region}

An International Mobile Subscriber Identity or IMSI (pronounced /ˈɪmziː/) is a unique identification associated with all GSM and UMTS network mobile phone users. It is stored as a 64 bit field in the SIM inside the phone and is sent by the phone to the network. It is also used for acquiring other details of the mobile in the Home Location Register (HLR) or as locally copied in the Visitor Location Register. To prevent eavesdroppers identifying and tracking the subscriber on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated TMSI is sent instead.

The IMSI is used in any mobile network that interconnects with other networks, in particular CDMA and EVDO networks as well as GSM networks. This number is provisioned in the phone directly or in the R-UIM card (a CDMA analogue equivalent to a SIM card in GSM).

An IMSI is usually presented as a 15 digit long number, but can be shorter. For example MTN South Africa's old IMSIs that are still being used in the market are shown as 14 digits. The first 3 digits are the Mobile Country Code (MCC), and is followed by the Mobile Network Code (MNC), either 2 digits (European standard) or 3 digits (North American standard). The remaining digits are the mobile station identification number (MSIN) within the network's customer base.

The IMSI conforms to the ITU E.212 numbering standard.

Contents

Examples of IMSI numeric presentation

IMSI analysis

IMSI analysis is the process of examining a subscriber's IMSI to identify the network the IMSI belongs to, and whether subscribers from that network may use a given network (if they are not local subscribers, this requires a roaming agreement).

If the subscriber is not from the provider's network, the IMSI must be converted to a Global Title, which can then be used for accessing the subscriber's data in the remote HLR. This is mainly important for international mobile roaming. Outside North America the IMSI is converted to the Mobile Global Title (MGT) format, standard E.214, which is similar to but different from E.164 number (more or less a telephone number). E.214 provides a method to convert the IMSI into a number that can be used for routing to international SS7 switches. E.214 can be interpreted as implying that there are two separate stages of conversion; first determine the MCC and convert to E.164 country calling code then determine MNC and convert to national network code for the carrier's network. But this process is not used in practise and the GSM numbering authority has clearly stated that a one stage process is used [1].

Full article ▸

related documents
Extended Binary Coded Decimal Interchange Code
Multicast address
Executable and Linkable Format
Line code
Z-machine
Μ-law algorithm
Digital compositing
Interleaf
Control unit
Liberty BASIC
Single UNIX Specification
NeWS
Turbo Pascal
Frame (telecommunications)
Basic rate interface
Konqueror
Mozilla
Finger protocol
Virtual machine
Motorola 56000
Instructions per second
Rn (newsreader)
IBM 650
Multiple document interface
MIRC
Atari Transputer Workstation
Hitachi 6309
Automatic callback
Microsoft Groove
Berkeley DB