International Mobile Subscriber Identity
Encyclopedia
An International Mobile Subscriber Identity or IMSI (icon) 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. 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 (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 ITU
E.212 numbering standard.
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 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, SCCP is used to send the message to its final destination. For details, see Global Title Translation.
Translation rule:
so we get 284011234567890 becomes 359881234567890 numbering plan E.214.
Translation rule:
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
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.
Universal Mobile Telecommunications System
Universal Mobile Telecommunications System is a third generation mobile cellular technology for networks based on the GSM standard. Developed by the 3GPP , UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for...
network mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
users. It is stored as a 64 bit field in the SIM
Subscriber Identity Module
A subscriber identity module or subscriber identification module is an integrated circuit that securely stores the International Mobile Subscriber Identity and the related key used to identify and authenticate subscriber on mobile telephony devices .A SIM is held on a removable SIM card, which...
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. This number is provisioned in the phone directly or in the R-UIM
R-UIM
Removable User Identity Module is a card developed for cdmaOne/CDMA2000 handsets that extends the GSM SIM card to CDMA phones and networks. To work in CDMA networks, the R-UIM contains an early version of the CSIM application. The card also contains SIM application, so it can work on both...
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
Mobile Network Code
A Mobile Network Code is used in combination with a Mobile Country Code to uniquely identify a mobile phone operator/carrier using the GSM/LTE, CDMA, iDEN, TETRA and UMTS public land mobile networks and some satellite mobile networks...
(MNC), either 2 digits (Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
an standard) or 3 digits (North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
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 ITU
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
E.212 numbering standard.
Examples of IMSI numeric presentation
| MCC | 404 | India India India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world... |
|---|---|---|
| MNC | 68 | MTNL delhi |
| MSIN | 5505601234 | |
| MCC | 310 | USA United States The United States of America is a federal constitutional republic comprising fifty states and a federal district... |
|---|---|---|
| MNC | 150 | AT&T Mobility |
| MSIN | 123456789 | |
| MCC | 460 | CHINA China Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture... |
|---|---|---|
| MNC | 00 | CMCC China Mobile China Mobile Limited is a Chinese state-owned telecommunication company that provides mobile voice and multimedia services through its nationwide mobile telecommunications network, the largest of its kind in the world... |
| MSIN | 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 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
Roaming
In wireless telecommunications, roaming is a general term referring to the extension of connectivity service in a location that is different from the home location where the service was registered. Roaming ensures that the wireless device is kept connected to the network, without losing the...
. Outside North America the IMSI is converted to the Mobile Global Title (MGT) format, standard E.214
E.214
E.214 is a numbering plan used for delivering mobility management related messages in GSM networks. The E.214 number is derived from the IMSI E.212 numbers are composed of two parts. The first, the E.164 part, is made up of a country code followed by the network code. The second part of the...
, which is similar to but different from E.164
E.164
E.164 is an ITU-T recommendation that defines the international public telecommunication numbering plan used in the PSTN and some other data networks. It also defines the format of telephone numbers. E.164 numbers can have a maximum of fifteen digits and are usually written with a + prefix...
number (more or less a telephone number). E.214
E.214
E.214 is a numbering plan used for delivering mobility management related messages in GSM networks. The E.214 number is derived from the IMSI E.212 numbers are composed of two parts. The first, the E.164 part, is made up of a country code followed by the network code. The second part of the...
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 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, 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 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 TitleGlobal TitleA Global Title is an address used in the SCCP protocol for routing signaling messages on telecommunications networks. In theory, a global title is a unique address which refers to only one destination, though in practice destinations can change over time....
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 E.164 country code + Network Code for Cingular)
- mark the number as having E.214 numbering plan.
- route message on Global TitleGlobal TitleA Global Title is an address used in the SCCP protocol for routing signaling messages on telecommunications networks. In theory, a global title is a unique address which refers to only one destination, though in practice destinations can change over time....
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 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 TitleGlobal TitleA Global Title is an address used in the SCCP protocol for routing signaling messages on telecommunications networks. In theory, a global title is a unique address which refers to only one destination, though in practice destinations can change over time....
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.