The international mobile subscriber identity (IMSI) is a number that uniquely identifies every user of a
cellular network. It is stored as a 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
Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobi ...
(HLR) or as locally copied in the
visitor location register
Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobile ...
. To prevent
eavesdropper
Eavesdropping is the act of secretly or stealthily listening to the private conversation or communications of others without their consent in order to gather information.
Etymology
The verb ''eavesdrop'' is a back-formation from the noun ''eaves ...
s from 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. For
GSM
The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...
,
UMTS
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the In ...
and
LTE networks, this number was provisioned in the
SIM card and for
cdmaOne
Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology. It was developed by Qualcomm and later adopted as a standard by the Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995. Th ...
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 Both cards have been superseded by the
UICC.
An IMSI is usually presented as a 15-digit number but can be shorter. For example,
MTN South Africa
MTN Group Limited, formerly M-Cell, is a South African multinational mobile telecommunications company, operating in many African and Asian countries. Its head office is in Johannesburg. , MTN recorded 280 million subscribers, making it the ...
's old IMSIs that are still in use in the market are 14 digits long. The first 3 digits represent the
mobile country code
The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC).
Overview
The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
(MCC), which is followed by the
mobile network code
The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC).
Overview
The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
(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.
3GPP specification 23.003
Release 14.3.0 (2017-03), 2.2 "Composition of IMSI" The remaining digits are the mobile subscription identification number
The mobile identification number (MIN) or mobile subscription identification number (MSIN) refers to the 10- digit unique number that a wireless carrier uses to identify a mobile phone, which is the last part of the international mobile subscriber ...
(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 ITU
The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
E.212 numbering standard.
IMSIs can sometimes be mistaken for the ICCID
A typical SIM card (mini-SIM with micro-SIM cutout)
A GSM mobile phone">Global System for Mobile Communications">GSM mobile phone
iPhone_6s.html"_;"title="T-Mobile_nano-SIM_card_with_NFC_capabilities_in_the_SIM_tray_of_an_iPhone_6s">T-Mobile_ ...
( 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
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 an E.164 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 practice and the GSM numbering authority has clearly stated that a one-stage process is use
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
The ITU-T Recommendation E.212 defines mobile country codes (MCC) as well as mobile network codes (MNC).
Overview
The mobile country code consists of three decimal digits and the mobile network code consists of two or three decimal digits (for e ...
+ MobilTel MNC)''
* identify this as belonging to MobilTel-Bulgaria network
* remove first five digits ''(length of MCC+MNC)''
* prepend 35988 ''(Bulgaria 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 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
Therefore, 310150123456789 becomes 14054123456789 under the E.214 numbering plan.
The result is an E.214 compliant Global Title, (Numbering Plan Indicator
A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, rea ...
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 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
In telecommunication, a public land mobile network (PLMN) is a combination of wireless communication services offered by a specific operator in a specific country.3GPP TS 21.905 https://www.etsi.org/deliver/etsi_tr/121900_121999/121905/15.00.00_6 ...
.
See also
* IMEI
The International Mobile Equipment Identity (IMEI) is a numeric identifier, usually unique, for 3GPP and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone but can al ...
* MSISDN
* MEID
A mobile equipment identifier (MEID) is a globally unique number identifying a physical piece of CDMA2000 mobile station equipment. The number format is defined by th3GPP2 report S.R0048but in practical terms, it can be seen as an IMEI but with ...
* Electronic Serial Number
* IMSI-catcher
An international mobile subscriber identity-catcher, or IMSI-catcher, is a telephone eavesdropping device used for intercepting mobile phone traffic and tracking location data of mobile phone users. Essentially a "fake" mobile tower acting betwe ...
References
External links
"Cellular Networking Perspectives" article in Wireless Telecom Magazine
* ttps://www.numberingplans.com/?page=analysis&sub=imsinr IMSI Lookup Utility
Explanation of GSM numbering plans
{{Mobile telecommunications standards
International telecommunications
Unique identifiers
3GPP standards