View source for IMSI

An '''[[International Mobile Subscriber Identity]]''' or '''[[IMSI]]'''  is a unique identification associated with all [[GSM]] and [[Universal Mobile Telecommunications System|UMTS]] network [[mobile phone]] users.  It is stored as a 64 bit field in the [[Subscriber Identity Module|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 [[eavesdropper]]s 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. 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)|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 ([[Europe]]an standard) or 3 digits ([[North America]]n standard). The length of the MNC depends on the value of the MCC. The remaining digits are the Mobile Subscription Identification Number (MSIN) within the network's customer base.

The IMSI conforms to the [[International Telecommunication Union|ITU]] E.212 numbering standard.

==Examples of IMSI numeric presentation==
{|
|+ IMSI:404685505601234
!MCC
|404
|[[India]]
|-
!MNC
|68
|[[MTNL delhi]]
|-
!MSIN
|colspan=2|5505601234
|}

{|
|+ IMSI: 310150123456789
!MCC
|310
|[[United States|USA]]
|-
!MNC
|150
|[[AT&T Mobility]]
|-
!MSIN
|colspan=2|123456789
|}


{|
|+ IMSI: 460001234567890
!MCC
|460
|[[CHINA]]
|-
!MNC
|00
|[[China_Mobile|CMCC]]
|-
!MSIN
|colspan=2|1234567890
|}

== 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#Roaming_agreements|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 [[Home Location Register|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 [[Signaling System 7|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 [[List of country calling codes|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 [http://www.ifast.org/files/IFAST22_015_GSMNALetter.pdf].

In North America, the IMSI is directly converted to an E.212 number with no modification of its value.  This can be routed directly on American SS7 networks.  

After this conversion, [[Signalling Connection Control Part|SCCP]] is used to send the message to its final destination.  For details, see [[Global Title Translation]].

=== Example of outside World Area 1 ===
This example shows the actual practice which is not clearly described in the standards.

Translation rule: 
* match numbers starting 28401 ''(Bulgaria [[mobile country code]] + MobilTel MNC)''
* identify this as belonging to MobilTel-Bulgaria network
* remove first five digits ''(length of MCC+MNC)''
* add 35988 ''(Bulgaria [[List of country calling codes|E.164 country code]] + a Bulgarian local prefix reaching MobilTel's network)''
* mark the number as having E.214 numbering plan.
* route message on [[Global Title]] across SCCP network
so we get 284011234567890 becomes 359881234567890 numbering plan E.214.

Translation rule: 
* match numbers starting 310150 ''(America first MCC + Cingular MNC)''
* remove first ''six'' digits ''(length of MCC+MNC)''
* add 14054 ''(North America [[List of country calling codes|E.164 country code]] + Network Code for Cingular)''
* mark the number as having E.214 numbering plan.
* route message on '''[[Global Title]]''' across SCCP network
so we get 310150123456789 becomes 14054123456789 numbering plan E.214.

The result is an E.214 compliant Global Title, ([[Numbering Plan Indicator]]
is set to 7 in the SCCP message).  This number can now be
sent to Global Title Analysis.
by onmobile

=== Example inside World Area 1 (North America) ===
Translation rule: 
* match numbers starting 28401 ''(Bulgaria [[Mobile country code|MCC]] + MobilTel MNC)''
* identify this as belonging to MobilTel-Bulgaria network
* do not alter the digits of the number
* mark the number as having E.212 numbering plan.
* route message on [[Global Title]] across SCCP network
so we get 284011234567890 becomes 284011234567890 numbering plan E.212. 

This number has to be converted on the ANSI to ITU boundary.  For more details please see [[Global Title Translation]].

== Home Network Identity ==
The Home Network Identity (HNI) is the combination of the MCC and the MNC.  This is the number which fully identifies a subscriber's home network. This combination is also known as the [[PLMN]].

==See also==
* [[IMEI]]
* [[MEID]]
* [[Electronic Serial Number]]
* [[MSISDN]]
* [[IMSI-catcher]]

==External links==
* [http://www.cnp-wireless.com/ArticleArchive/Wireless%20Telecom/2001Q1WT.html "Cellular Networking Perspectives" article in Wireless Telecom Magazine]
* [http://www.atis.org/ATIS/IOC/iochom.htm IMSI oversight council responsible for allocating IMSI ranges in the USA]
* [https://www.numberingplans.com/?page=analysis&sub=imsinr IMSI Lookup Utility]
* [http://www.mib.net.ua/2008/03/gsm-numbering-plans-en.html Explanation of GSM numbering plans]
* [http://www.imsi.biz/ IMSI formats]