The international mobile subscriber identity ( IMSI ; / ˈ ɪ m z iː / ) is a number that uniquely identifies every user of a cellular network . It is stored as a 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 eavesdroppers 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.
41-511: [REDACTED] Look up imsi in Wiktionary, the free dictionary. IMSI may refer to: International mobile subscriber identity Intracytoplasmic morphologically selected sperm injection Interface Marketing Supplier Integration Institute , standards organization Idaho Maximum Security Institution , prison International Maple Syrup Institute , see maple syrup IMSI/Design ,
82-590: 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
123-401: A one-stage process is used [1] . 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 . This example shows the actual practice which is not clearly described in
164-498: 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
205-410: A rule, these are stolen or lost devices. Mobile operators rarely use EIR capabilities to block devices on their own. Usually blocking begins when there is a law in the country, which obliges all cellular operators of the country to do so. Therefore, in the delivery of the basic components of the network switching subsystem (core network) is often already present EIR with basic functionality, which includes
246-476: A software company, see List of CAx companies Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title IMSI . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=IMSI&oldid=874365205 " Category : Disambiguation pages Hidden categories: Short description
287-446: A specific service number, sending SMS to a specific service number, and all Internet traffic is redirected to a specific landing page. This is achieved by the fact that EIR can send commands to several MNO systems (HLR, PCRF , SMSC , etc.). The most common suppliers of individual EIR systems (not as part of a complex solution) are the companies BroadForward, Mahindra Comviva, Mavenir, Nokia, Eastwind. Connected more or less directly to
328-537: A time. The HLRs store details of every SIM card issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the primary key to each HLR record. Another important item of data associated with the SIM are the MSISDNs, which are the telephone numbers used by mobile phones to make and receive calls. The primary MSISDN is the number used for making and receiving voice calls and SMS, but it
369-614: A ‘whitelisted’ response to all CheckIMEI and the ability to fill IMEI blacklist, which will be given a ‘blacklisted’ response. When the legislative framework for blocking registration of devices in cellular networks appears in the country, the telecommunications regulator usually has a Central EIR ( CEIR ) system, which is integrated with the EIR of all operators and transmits to them the actual lists of identifiers that must be used when processing CheckIMEI requests. In doing so, there may be many new requirements for EIR systems that are not present in
410-583: Is a database of the MSs ( Mobile stations ) that have roamed into the jurisdiction of the Mobile Switching Center (MSC) which it serves. Each main base transceiver station in the network is served by exactly one VLR (one BTS may be served by many MSCs in case of MSC in pool), hence a subscriber cannot be present in more than one VLR at a time. The data stored in the VLR has either been received from
451-517: Is allowed to attach and proceed with GSM services. After successful authentication, the MSC sends the encryption key K c to the base station controller (BSC) so that all communications can be encrypted and decrypted. Of course, the mobile phone can generate the K c itself by feeding the same RAND supplied during authentication and the K i into the A8 algorithm. The AuC is usually collocated with
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#1732779862628492-468: Is an additional form of identification check performed on the serial number of the mobile phone described in the EIR section below, but this is not relevant to the AuC processing. Proper implementation of security in and around the AuC is a key part of an operator's strategy to avoid SIM cloning . The AuC does not engage directly in the authentication process, but instead generates data known as triplets for
533-412: Is available in 3GPP TS 23.205. The term Circuit switching (CS) used here originates from traditional telecommunications systems. However, modern MSS and MGW devices mostly use generic Internet technologies and form next-generation telecommunication networks . MSS software may run on generic computers or virtual machines in cloud environment. The MSC connects to the following elements: Tasks of
574-578: Is different from Wikidata All article disambiguation pages All disambiguation pages International mobile subscriber identity The IMSI is used in any mobile network that interconnects with other networks. For GSM , UMTS and LTE networks, this number was provisioned in the SIM card and for cdmaOne and CDMA2000 networks, in the phone directly or in the R-UIM card (the CDMA equivalent of
615-471: Is possible for a SIM to have other secondary MSISDNs associated with it for fax and data calls. Each MSISDN is also a unique key to the HLR record. The HLR data is stored for as long as a subscriber remains with the mobile phone operator. Examples of other data stored in the HLR against an IMSI record is: The HLR is a system which directly receives and processes MAP transactions and messages from elements in
656-430: 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 phone operators and allows mobile devices to communicate with each other and telephones in the wider public switched telephone network (PSTN). The architecture contains specific features and functions which are needed because
697-518: 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. 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
738-434: Is used to authenticate the customer and generate a key for encrypting voice and data traffic, as defined in 3GPP TS 43.020 (03.20 before Rel-4). Development of A3 and A8 algorithms is considered a matter for individual GSM network operators, although example implementations are available. To encrypt Global System for Mobile Communications (GSM) cellular communications A5 algorithm is used. The Visitor Location Register (VLR)
779-593: The Home Location Register (HLR) , or collected from the MS. In practice, for performance reasons, most vendors integrate the VLR directly to the V-MSC and, where this is not done, the VLR is very tightly linked with the MSC via a proprietary interface. Whenever an MSC detects a new MS in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of
820-485: The Internet . The mobile switching center (MSC) is the primary service delivery node for GSM/CDMA, responsible for routing voice calls and SMS as well as other services (such as conference calls, FAX, and circuit-switched data). The MSC sets up and releases the end-to-end connection , handles mobility and hand-over requirements during the call and takes care of charging and real-time prepaid account monitoring. In
861-492: The gsm core network (typically when the phone is powered on). Once the authentication is successful, the HLR is allowed to manage the SIM and services described above. An encryption key is also generated that is subsequently used to encrypt all wireless communications (voice, SMS, etc.) between the mobile phone and the GSM core network. If the authentication fails, then no services are possible from that particular combination of SIM card and mobile phone operator attempted. There
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#1732779862628902-590: 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 . 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 . Home Location Register Network switching subsystem ( NSS ) (or GSM core network )
943-456: The EIR response to determine whether or not to allow the device to register or re-register on the network. Since the response of switching equipment to ‘greylisted’ and ‘unknown equipment’ responses is not clearly described in the standard, they are most often not used. Most often, EIR uses the IMEI blacklist feature, which contains the IMEI of the devices that need to be banned from the network. As
984-772: The GSM core network are many other functions. The billing center is responsible for processing the toll tickets generated by the VLRs and HLRs and generating a bill for each subscriber. It is also responsible for generating billing data of roaming subscriber. The multimedia messaging service center supports the sending of multimedia messages (e.g., images, audio , video and their combinations) to (or from) MMS-bluetooth. The voicemail system records and stores voicemail. According to U.S. law, which has also been copied into many other countries, especially in Europe, all telecommunications equipment must provide facilities for monitoring
1025-537: The GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent digitally encoded directly to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound is encoded digitally as a pulse-code modulation (PCM) signal in a 64-kbit/s timeslot, known as a DS0 in America). There are various different names for MSCs in different contexts which reflects their complex role in
1066-408: The GSM network, for example, the location update messages received as mobile phones roam around. The HLR connects to the following elements: The main function of the HLR is to manage the fact that SIMs and phones move around a lot. The following procedures are implemented to deal with this: The authentication center (AuC) is a function to authenticate each SIM card that attempts to connect to
1107-499: The HLR, although this is not necessary. Whilst the procedure is secure for most everyday use, it is by no means hack proof. Therefore, a new set of security methods was designed for 3G phones. In practice, A3 and A8 algorithms are generally implemented together (known as A3/A8, see COMP128 ). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centers. It
1148-515: The MNC depends on the value of the MCC, and it is recommended that the length is uniform within a MCC area. 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 ITU E.212 numbering standard. IMSIs can sometimes be mistaken for the ICCID ( E.118 ), which
1189-427: The MSC include: The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM core network. There can be several logical, and physical, HLRs per public land mobile network (PLMN), though one international mobile subscriber identity (IMSI)/MSISDN pair can be associated with only one logical HLR (which can span several physical nodes) at
1230-461: The MSC to use during the procedure. The security of the process depends upon a shared secret between the AuC and the SIM called the K i . The K i is securely burned into the SIM during manufacture and is also securely replicated onto the AuC. This K i is never transmitted between the AuC and SIM, but is combined with the IMSI to produce a challenge/response for identification purposes and an encryption key called K c for use in over
1271-601: The MSC. When a particular IMSI requests access to the GSM core network, the MSC sends the RAND part of the triplet to the SIM. The SIM then feeds this number and the K i (which is burned onto the SIM) into the A3 algorithm as appropriate and an SRES is calculated and sent back to the MSC. If this SRES matches with the SRES in the triplet (which it should if it is a valid SIM), then the mobile
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1312-486: 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 '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
1353-405: The air communications. The AuC connects to the following elements: The AuC stores the following data for each IMSI: When the MSC asks the AuC for a new set of triplets for a particular IMSI, the AuC first generates a random number known as RAND . This RAND is then combined with the K i to produce two numbers as follows: The numbers ( RAND , SRES, K c ) form the triplet sent back to
1394-413: The gateway function and the visited MSC function. However, some manufacturers design dedicated high capacity MSCs which do not have any base station subsystems (BSS) connected to them. These MSCs will then be the gateway MSC for many of the calls they handle. The visited MSC (V-MSC) is the MSC where a customer is currently located. The visitor location register (VLR) associated with this MSC will have
1435-419: The legacy EIR: Other functions may be required in individual cases. For example, Kazakhstan has introduced mandatory registration of devices and their binding to subscribers. But when a subscriber appears in the network with a new device, the network operation is not blocked completely, and the subscriber is allowed to register the device. To do this, there are blocked all services, except the following: calls to
1476-531: The mobile switching center, which provides circuit-switched calling mobility management, and GSM services to the mobile phones roaming within the area that it serves. The functionality enables split control between (signaling ) and user plane (bearer in network element called as media gateway/MG), which guarantees better placement of network elements within the network. MSS and media gateway (MGW) makes it possible to cross-connect circuit-switched calls switched by using IP, ATM AAL2 as well as TDM . More information
1517-504: The network, all of these terms though could refer to the same MSC, but doing different things at different times. The gateway MSC (G-MSC) is the MSC that determines which "visited MSC" (V-MSC) the subscriber who is being called is currently located at. It also interfaces with the PSTN. All mobile to mobile calls and PSTN to mobile calls are routed through a G-MSC. The term is only valid in the context of one call, since any MSC may provide both
1558-480: The new location of that MS. If VLR data is corrupted it can lead to serious issues with text messaging and call services. Data stored include: The primary functions of the VLR are: EIR is a system that handles real-time requests to check the IMEI (checkIMEI) of mobile devices that come from the switching equipment (MSC, SGSN , MME ). The answer contains the result of the check: The switching equipment must use
1599-459: The phones are not fixed in one location. The NSS originally consisted of the circuit-switched core network , used for traditional GSM services such as voice calls, SMS , and circuit switched data calls. It was extended with an overlay architecture to provide packet-switched data services known as the GPRS core network . This allows mobile phones to have access to services such as WAP , MMS and
1640-522: The standards. Translation rule: Therefore, 284011234567890 becomes 359881234567890 under the E.214 numbering plan. Translation rule: 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. Translation rule: Therefore, 284011234567890 becomes 284011234567890 under
1681-408: The subscriber's data in it. The anchor MSC is the MSC from which a handover has been initiated. The target MSC is the MSC toward which a handover should take place. A mobile switching center server is a part of the redesigned MSC concept starting from 3GPP Release 4 . The mobile switching center server is a soft-switch variant (therefore it may be referred to as mobile soft switch, MSS) of