Switching And Management Subsystem
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Network switching subsystem (NSS) (or GSM core network) is the component of a
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 as ...
system that carries out call out and
mobility management Mobility management is one of the major functions of a GSM or a UMTS network that allows mobile phones to work. The aim of mobility management is to track where the subscribers are, allowing calls, SMS and other mobile phone services to be deli ...
functions for
mobile phones A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...
roaming Roaming is a wireless telecommunication term typically used with mobile devices, such as mobile phones. It refers to a mobile phone being used outside the range of its native network and connecting to another available cell network. Technical ...
on the network of base stations. It is owned and deployed by
mobile phone operator A mobile phone operator, wireless provider, or carrier is a mobile telecommunications company that provides wireless Internet GSM services for mobile device users. The operator gives a SIM card to the customer who inserts it into the mobile dev ...
s and allows mobile devices to communicate with each other and
telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
s in the wider
public switched telephone network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...
(PSTN). The architecture contains specific features and functions which are needed because the phones are not fixed in one location. The NSS originally consisted of the circuit-switched
core network A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building ...
, used for traditional
GSM services GSM services are a standard collection of applications and features available over the Global System for Mobile Communications (GSM) to mobile phone subscribers all over the world. The GSM standards are defined by the 3GPP collaboration and imp ...
such as voice calls,
SMS Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
, and
circuit switched data In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM). After 2010 many teleco ...
calls. It was extended with an overlay architecture to provide packet-switched data services known as the
GPRS core network The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet. The GPRS system is an integrated part of the G ...
. This allows mobile phones to have access to services such as
WAP WAP or Wap may refer to: Music * "WAP" (song), a 2020 song by Cardi B featuring Megan Thee Stallion Organizations * Weatherization Assistance Program, for US energy costs * Western Australia Party, a political party founded in 2016 * Western A ...
,
MMS MMS may refer to: Science and technology Network communication protocols * Multimedia Messaging Service for mobile phones * Microsoft Media Server, a content-streaming protocol (mms://) * Manufacturing Message Specification for real time proces ...
and the
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
.


Mobile switching center (MSC)


Description

The mobile switching center (MSC) is the primary service delivery node for GSM/CDMA, responsible for
routing Routing is the process of selecting a path for traffic in a network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched telephone netw ...
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 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 Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the ...
(PCM) signal in a 64-kbit/s timeslot, known as a
DS0 Digital Signal 0 (DS0) is a basic digital signaling rate of 64 kilobits per second (kbit/s), corresponding to the capacity of one analog voice-frequency-equivalent communication channel. The DS0 rate, and its equivalents E0 in the E-carrier system ...
in America). There are various different names for MSCs in different contexts which reflects their complex role in 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 the gateway function and the visited MSC function. However, some manufacturers design dedicated high capacity MSCs which do not have any
base station subsystem The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone and the network switching subsystem. The BSS carries out transcoding of s ...
s (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 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 ...
(VLR) associated with this MSC will have the subscriber's data in it. The anchor MSC is the MSC from which a
handover In cellular telecommunications, handover, or handoff, is the process of transferring an ongoing call or data session from one channel connected to the core network to another channel. In satellite communications it is the process of transfe ...
has been initiated. The target MSC is the MSC toward which a handover should take place. A
mobile switching center server The mobile switching station, abbreviated as MSC Server or MSS, is a 2G core network element which controls the network switching subsystem elements. Alternatively or adaptively, MSS can be used in GSM networks as well, if the manufacturer has im ...
is a part of the redesigned MSC concept starting from 3GPP Release 4.


Mobile switching center server (MSC-Server, MSCS or MSS)

The mobile switching center server is a soft-switch variant (therefore it may be referred to as mobile soft switch, MSS) of the mobile switching center, which provides circuit-switched calling mobility management, and GSM services to the mobile phones
roaming Roaming is a wireless telecommunication term typically used with mobile devices, such as mobile phones. It refers to a mobile phone being used outside the range of its native network and connecting to another available cell network. Technical ...
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 TDM may refer to: * ''TDM (film), TDM'', a 2023 Indian Marathi language, Marathi comedy film * TDM (Macau) (), a Macanese radio and television network * The Yamaha TDM, a motorcycle model * Target Disk Mode, a boot mode on certain Macintosh compute ...
. More information is available in 3GPP TS 23.205. The term
Circuit switching Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full b ...
(CS) used here originates from traditional telecommunications systems. However, modern MSS and MGW devices mostly use generic
Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
technologies and form next-generation telecommunication networks. MSS software may run on generic computers or
virtual machine In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardw ...
s in
cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may co ...
environment.


Other GSM core network elements connected to the MSC

The MSC connects to the following elements: * 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 mobile ...
(HLR) for obtaining data about the SIM and mobile services ISDN number (MSISDN; i.e., the telephone number). * The base station subsystems (BSS) which handles the radio communication with 2G and 2.5G mobile phones. * The
UMTS terrestrial radio access network UTRAN (short for "UMTS Terrestrial Radio Access Network''") is a collective term for the network and equipment that connects mobile handsets to the public telephone network or the Internet. It contains the base stations, which are called Node B's ...
(UTRAN) which handles the radio communication with 3G mobile phones. * 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 ...
(VLR) provides subscriber information when the subscriber is outside its home network. * Other MSCs for procedures such as
hand over A Hand-Over is a term used in the animation industry to refer to the process of adding finger and hand motion capture data to the pre-existing full-body motion capture data, using a hand motion capture device. Techniques A Hand-Over is accomplis ...
.


Procedures implemented

Tasks of the MSC include: * Delivering calls to subscribers as they arrive based on information from the VLR. * Connecting outgoing calls to other mobile subscribers or the PSTN. * Delivering SMSs from subscribers to the
short message service center A Short Message Service Center (SMSC) is a network element in the mobile telephone network. Its purpose is to store, forward, convert and deliver Short Message Service (SMS) messages. The full designation of an SMSC according to 3GPP is ''Sh ...
(SMSC) and vice versa. * Arranging handovers from BSC to BSC. * Carrying out handovers from this MSC to another. * Supporting
supplementary services The term supplementary can refer to: * Supplementary angles * Supplementary Benefit, a former benefit payable in the United Kingdom * Supplementary question A question time in a parliament occurs when members of the parliament ask questions of ...
such as conference calls or call hold. * Generating billing information.


Home location register (HLR)

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 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 ...
(PLMN), though one
international mobile subscriber identity 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 th ...
(IMSI)/MSISDN pair can be associated with only one logical HLR (which can span several physical nodes) at a time. The HLRs store details of every
SIM card file:SIM-Karte von Telefónica O2 Europe - Standard und Micro.jpg, A typical SIM card (mini-SIM with micro-SIM cutout) file:Sim card.png, A smart card taken from a Global System for Mobile Communications, GSM mobile phone file:Simkarte NFC SecureE ...
issued by the mobile phone operator. Each SIM has a unique identifier called an IMSI which is the
primary key In the relational model of databases, a primary key is a ''specific choice'' of a ''minimal'' set of attributes (Column (database), columns) that uniquely specify a tuple (Row (database), row) in a Relation (database), relation (Table (database), t ...
to each HLR record. Another important item of data associated with the SIM are the MSISDNs, which are the
telephone number A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...
s 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 is possible for a SIM to have other secondary MSISDNs associated with it for
fax Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer o ...
and data calls. Each MSISDN is also a
unique key In relational database management systems, a unique key is a candidate key that is not the primary key of the relation. All the candidate keys of a relation can uniquely identify the records of the relation, but only one of them is used as the prima ...
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: * GSM services that the subscriber has requested or been given. *
General Packet Radio Service General Packet Radio Service (GPRS) is a packet oriented mobile data standard on the 2G and 3G cellular communication network's global system for mobile communications (GSM). GPRS was established by European Telecommunications Standards Inst ...
(GPRS) settings to allow the subscriber to access packet services. * Current location of subscriber (VLR and
serving GPRS support node The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet. The GPRS system is an integrated part of the G ...
/SGSN). * Call divert settings applicable for each associated MSISDN. The HLR is a system which directly receives and processes
MAP A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes. Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although ...
transactions and messages from elements in the GSM network, for example, the location update messages received as mobile phones roam around.


Other GSM core network elements connected to the HLR

The HLR connects to the following elements: * The G-MSC for handling incoming calls * The VLR for handling requests from mobile phones to attach to the network * The SMSC for handling incoming SMSs * The
voice mail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows users and subscribers to exchange personal voice messages; to select and deliver voice information; and to process transactions relating to ind ...
system for delivering notifications to the mobile phone that a message is waiting * The AuC for authentication and ciphering and exchange of data (triplets)


Procedures implemented

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: * Manage the mobility of subscribers by means of updating their position in administrative areas called 'location areas', which are identified with a LAC. The action of a user of moving from one LA to another is followed by the HLR with a Location area update procedure. * Send the subscriber data to a VLR or SGSN when a subscriber first roams there. * Broker between the G-MSC or SMSC and the subscriber's current VLR in order to allow incoming calls or text messages to be delivered. * Remove subscriber data from the previous VLR when a subscriber has roamed away from it. * Responsible for all SRI related queries (i.e. for invoke SRI, HLR should give sack SRI or SRI reply).


Authentication center (AuC)


Description

The authentication center (AuC) is a function to
authenticate Authentication (from ''authentikos'', "real, genuine", from αὐθέντης ''authentes'', "author") is the act of proving an assertion, such as the identity of a computer system user. In contrast with identification, the act of indicatin ...
each
SIM card file:SIM-Karte von Telefónica O2 Europe - Standard und Micro.jpg, A typical SIM card (mini-SIM with micro-SIM cutout) file:Sim card.png, A smart card taken from a Global System for Mobile Communications, GSM mobile phone file:Simkarte NFC SecureE ...
that attempts to connect to 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 A key in cryptography is a piece of information, usually a string of numbers or letters that are stored in a file, which, when processed through a cryptographic algorithm, can encode or decode cryptographic data. Based on the used method, the key c ...
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 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 Phone cloning is the copying of identity from one cellular device to another. AMPS cloning Analogue mobile telephones were notorious for their lack of security. Casual listeners easily heard conversations as plain narrowband FM; eavesdropper ...
. The AuC does not engage directly in the authentication process, but instead generates data known as ''triplets'' for the MSC to use during the procedure. The security of the process depends upon a
shared secret In cryptography, a shared secret is a piece of data, known only to the parties involved, in a secure communication. This usually refers to the key of a symmetric cryptosystem. The shared secret can be a password, a passphrase, a big number, or a ...
between the AuC and the SIM called the ''Ki''. The ''Ki'' is securely burned into the SIM during manufacture and is also securely replicated onto the AuC. This ''Ki'' 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 ''Kc'' for use in over the air communications.


Other GSM core network elements connected to the AuC

The AuC connects to the following elements: * The MSC which requests a new batch of triplet data for an IMSI after the previous data have been used. This ensures that same keys and challenge responses are not used twice for a particular mobile.


Procedures implemented

The AuC stores the following data for each IMSI: * the ''Ki'' * Algorithm id. (the standard algorithms are called A3 or A8, but an operator may choose a proprietary one). 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 ''Ki'' to produce two numbers as follows: * The ''Ki'' and ''RAND'' are fed into the A3 algorithm and the signed response (SRES) is calculated. * The ''Ki'' and ''RAND'' are fed into the A8 algorithm and a session key called ''Kc'' is calculated. The numbers (''RAND'', SRES, ''Kc'') form the triplet sent back to 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 ''Ki'' (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 is allowed to attach and proceed with GSM services. After successful authentication, the MSC sends the encryption key ''Kc'' to the
base station controller The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone and the network switching subsystem. The BSS carries out transcoding of s ...
(BSC) so that all communications can be encrypted and decrypted. Of course, the mobile phone can generate the ''Kc'' itself by feeding the same RAND supplied during authentication and the ''Ki'' into the A8 algorithm. The AuC is usually collocated with 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 The COMP128 algorithms are implementations of the A3 and A8 functions defined in the GSM standard. A3 is used to authenticate the mobile station to the network. A8 is used to generate the session key used by A5 to encrypt the data transmitted be ...
). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centers. It 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.


Visitor location register (VLR)


Description

The Visitor Location Register (VLR) is a database of the MSs (
Mobile station A mobile station (MS) comprises all user equipment and computer software, software needed for communication with a Cellular network, mobile network. The term refers to the global system connected to the mobile network, i.e. a mobile phone or mob ...
s) that have roamed into the jurisdiction of the Mobile Switching Center (MSC) which it serves. Each main
base transceiver station A base transceiver station (BTS) is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets), WLL phones, computers with wireless Internet connectivity, o ...
in the network is served by exactly one VLR (one
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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 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 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: * IMSI (the subscriber's identity number). * Authentication data. * MSISDN (the subscriber's phone number). * GSM services that the subscriber is allowed to access. * access point (GPRS) subscribed. * The HLR address of the subscriber. * SCP Address(For Prepaid Subscriber).


Procedures implemented

The primary functions of the VLR are: * To inform the HLR that a subscriber has arrived in the particular area covered by the VLR. * To track where the subscriber is within the VLR area (location area) when no call is ongoing. * To allow or disallow which services the subscriber may use. * To allocate roaming numbers during the processing of incoming calls. * To purge the subscriber record if a subscriber becomes inactive whilst in the area of a VLR. The VLR deletes the subscriber's data after a fixed time period of inactivity and informs the HLR (e.g., when the phone has been switched off and left off or when the subscriber has moved to an area with no coverage for a long time). * To delete the subscriber record when a subscriber explicitly moves to another, as instructed by the HLR.


Equipment identity register (EIR)

EIR is a system that handles real-time requests to check the
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 also ...
(checkIMEI) of mobile devices that come from the switching equipment (MSC,
SGSN The GPRS core network is the central part of the general packet radio service (GPRS) which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet. The GPRS system is an integrated part of the G ...
, MME). The answer contains the result of the check: * whitelisted – the device is allowed to register on the network. * blacklisted – the device is prohibited from registering on the network. * greylisted – the device is allowed to register on the network temporarily. * An error ‘unknown equipment’ may also be returned. The switching equipment must use 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 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 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 the legacy EIR: * Synchronizing lists with CEIR. CEIR systems are not described by a standard, so the protocols and exchange mode may differ from country to country. * Supporting additional lists – IMEI white list, IMEI grey list, list of allocated
TACs Total Access Communication System (TACS) and ETACS are variants of Advanced Mobile Phone System (AMPS) which were announced as the choice for the first two UK national cellular systems in February 1983, less than a year after the UK government an ...
, etc. * Support in lists not only IMEI but also bindings – IMEI-IMSI, IMEI-MSISDN, IMEI- IMSI- MSISDN. * Supporting the customized logic of lists applying. * Automatic adding the item to a list in separate scenarios. * Sending
SMS Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...
notifications to subscribers in separate scenarios. * Integration with the billing system to receive IMSI-MSISDN bundles. * Accumulating the subscribers’ profiles (history of device changing). * Long-term storage of processing of all CheckIMEI requests. 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 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 Policy and Charging Rules Function (PCRF) is the software node designated in real-time to determine policy rules in a multimedia network. As a policy tool, the PCRF plays a central role in next-generation networks. Unlike earlier policy engines th ...
, 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, Svyazcom.


Other support functions

Connected more or less directly to the GSM core network are many other functions.


Billing center (BC)

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.


Multimedia messaging service center (MMSC)

The
multimedia messaging service Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia content to and from a mobile phone over a cellular network. Users and providers may refer to such a message as a PXT, a picture message, or a multimedia ...
center supports the sending of multimedia messages (e.g., images,
audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum *Digital audio, representation of sound ...
,
video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syste ...
and their combinations) to (or from) MMS-bluetooth.


Voicemail system (VMS)

The
voicemail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows users and subscribers to exchange personal voice messages; to select and deliver voice information; and to process transactions relating to ind ...
system records and stores voicemail.


Lawful interception functions

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 the calls of selected users. There must be some level of support for this built into any of the different elements. The concept of ''lawful interception'' is also known, following the relevant U.S. law, as CALEA. Generally, lawful Interception implementation is similar to the implementation of conference call. While A and B are talking with each other, C can join the call and listen silently.


See also

* The GSM core network. * Base station subsystem *COM 128 *4GLET


References


External links

* 4GLET - the standardisation body for GSM and UMTS
UMTS Networks: Protocols, Terminology and Implementation
- a PDF eBook by Gunnar Heine {{Mobile telecommunications standards GSM standard Telecommunications infrastructure