Editing International mobile subscriber identity

{{Short description|ITU-T recommendation}}
{{Infobox technology standard
| title = International Mobile Subscriber Identity
| long_name =
| caption =
| abbreviation = IMSI
| status = in force
| year_started = {{start date and age|1988|11|25}}
| version = (06/24)
| version_date = June 28, 2024
| preview =
| preview_date =
| organization = [[ITU-T]]
| committee =
| base_standards =
| related_standards =
| domain =
| license =
| website = {{URL|https://itu.int/rec/T-REC-E.212}}
}}
The '''international mobile subscriber identity''' ('''IMSI'''; {{IPAc-en|ˈ|ɪ|m|z|iː}}) is a number that uniquely identifies every user of a [[cellular network]].<ref>{{Cite web|url=https://www.itu.int/rec/T-REC-E.212|title=E.212 : The international identification plan for public networks and subscriptions|website=www.itu.int|access-date=2024-09-20}}</ref> It is stored as a {{nowrap|64-bit}} field and is sent by the mobile device 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 from identifying and tracking the subscriber on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated [[Mobility management#TMSI|TMSI]] is sent instead.{{cn|date=March 2025}}

The IMSI is used in ''any'' mobile network that interconnects with other networks. For [[GSM]], [[UMTS]] and [[LTE (telecommunication)|LTE]] networks, this number was provisioned in the [[subscriber identity module|SIM]] card and for [[cdmaOne]] and [[CDMA2000]] networks, in the phone directly or in the [[R-UIM]] card (the CDMA equivalent of the SIM card). Both cards have been superseded by the [[Universal integrated circuit card|UICC]].

An IMSI is usually presented as a 15-digit number but can be shorter. For example, [[MTN (South Africa)|MTN South Africa]]'s old IMSIs that are still in use in the market are 14 digits long. The first 3 digits represent the [[mobile country code]] (MCC), which is followed by the [[mobile network code]] (MNC), either 2-digit (European standard) or 3-digit (North American standard). The length of the MNC depends on the value of the MCC, and it is recommended that the length is uniform within a MCC area.<ref>[http://www.3gpp.org/DynaReport/23003.htm 3GPP specification 23.003] Release 14.3.0 (2017-03), 2.2 "Composition of IMSI"</ref> The remaining digits are the [[mobile subscription identification number]] (MSIN) within the network's customer base, usually 9 to 10 digits long, depending on the length of the MNC.

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

IMSIs can sometimes be mistaken for the [[SIM_card#ICCID|ICCID]] ([[E.118]]), which is the identifier for the physical SIM card itself (or now the virtual SIM card if it is an [[eSIM]]).  The IMSI lives as part of the profile (or one of several profiles if the SIM and operator support multi-IMSI SIMs) on the SIM/ICCID.

== Examples of IMSI numeric presentational ==
{| class="wikitable"
|+ IMSI:310170845466094
!MCC
|310
|[[United States]] 
|-
!MNC
|170
|[[Sprint Corporation|Sprint]]
|-
!MSIN
|colspan=2|845466094
|}

{| class="wikitable"
|+ IMSI:470040123456789
!MCC
|470
|[[Bangladesh]]
|-
!MNC
|04
|[[TeleTalk]]
|-
!MSIN
|colspan=2|0123456789
|}

{| class="wikitable"
|+ IMSI:502130123456789
!MCC
|502
|[[Malaysia]]
|-
!MNC
|13
|[[Celcom]]
|-
!MSIN
|colspan=2|0123456789
|}

{| class="wikitable"
|+ IMSI:460001357924680
!MCC
|460
|[[China]]
|-
!MNC
|00
|[[China Mobile|CMCC]] <!-- China Mobile Communications Corporation --> 
|-
!MSIN
|colspan=2|1357924680
|}

{| class="wikitable"
|+ IMSI:520031234567890
!MCC
|520
|[[Thailand]]
|-
!MNC
|03
|[[Advanced Info Service|AIS]] <!-- Advanced Info Service Public Company Limited --> 
|-
!MSIN
|colspan=2|1234567890
|}

{| class="wikitable"
|+ IMSI:313460000000001
!IMSI
|colspan=2|{{font color | blue | 313}} {{font color | green | 460}} 000 000 001
|-
!MCC
|{{font color | blue | 313}}
|[[United States]]
|-
!MNC
|{{font color | green | 460}}
|[[Mobi (company)|Mobi]]<ref>{{Cite web|url=http://imsiadmin.com/assignments|title = HNI Assignments &#124; IMSIAdmin}}</ref>
|-
!MSIN
|colspan=2|000000001
|-
!ICCID
|colspan=2|891{{font color | green | 460}} 0000 0000 0012<br />(89 is the [[ISO/IEC 7812|industry identifier]] for telecom and +1 is calling code)
|}

== 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).  <!-- some systems allow bypassing GT analysis, but I think this is confusing to mention, so we avoid the subject -->

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 an [[E.164]] 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 practice 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#Global title translation|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)''
* prepend 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
Therefore, 284011234567890 becomes 359881234567890 under the E.214 numbering plan.

Translation rule: 
* match numbers starting 310150 ''(America first MCC + Cingular MNC)''
* remove first ''six'' digits ''(length of MCC+MNC)''
* prepend 14054 ''(North America [[List of country calling codes|E.164 country code]] + Network Code for Cingular)''{{Citation needed|reason=Citation Needed for where '4054' comes from.|date=September 2011}}
* mark the number as having E.214 numbering plan.
* route message on '''[[Global Title]]''' across SCCP network
Therefore, 310150123456789 becomes 14054123456789 under the E.214 numbering plan.

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.

=== Example inside World Area 1 (North America) ===
Translation rule: 
* match number 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
Therefore, 284011234567890 becomes 284011234567890 under the E.212 numbering plan.

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]]
* [[MSISDN]]
* [[PLMN]]
* [[MEID]]
* [[Electronic Serial Number]]
* [[IMSI-catcher]]
* [[Telephone number]]

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20040607225011/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] {{Webarchive|url=https://web.archive.org/web/20040423215552/http://www.atis.org/ATIS/IOC/iochom.htm |date=2004-04-23 }}
* [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]

{{Mobile telecommunications standards}}

[[Category:International telecommunications]]
[[Category:Unique identifiers]]
[[Category:3GPP standards]]