Network Switching Subsystem
Encyclopedia
Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call switching
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 telephone
s in the wider Public Switched Telephone Network or (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
, 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 the Internet
.
All mobile phones manufactured today have both circuit and packet based services, so most operators have a GPRS network in addition to the standard GSM core network.
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 pre-paid account monitoring.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound encoded digitally as 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 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 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 BSS
s 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 VLR associated with this MSC will have 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 centre server
is a part of the redesigned MSC concept starting from 3GPP Release 4.
within the area that it serves. MSS functionality enables split between control (signalling) and user plane (bearer in network element called as media gateway/MG), which guarantees better placement of network elements within the network.
MSS and MGW media gateway
makes it possible to cross-connect circuit switched calls switched by using IP, ATM AAL2 as well as TDM. More information is available in 3GPP TS 23.205.
(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 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.
The next important items of data associated with the SIM are the MSISDNs, which are the telephone number
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
and data calls. Each MSISDN is also a primary key to the HLR record. The HLR data is stored for as long as a subscriber remains with the mobile phone operator.
MSISDN is not a distinguishable parameter in case of ported numbers. Instead, LRN and MSISDN combine to form a unique distinguishable parameter.
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 the GSM network, for example, the location update messages received as mobile phones roam around.
each SIM card 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 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.
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
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.
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 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 (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 crack proof. Therefore a new set of security methods was designed for 3G phones.
A3 Algorithm is used to encrypt Global System for Mobile Communications (GSM) cellular communications. In practice, A3 and A8 algorithms are generally implemented together (known as A3/A8). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centres. 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.
in the network is served by exactly one VLR, 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 HLR, or collected from the MS (Mobile station
). 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:
is often integrated to the HLR. The EIR keeps a list of mobile phones (identified by their IMEI) which are to be banned from the network or monitored. This is designed to allow tracking of stolen mobile phones. In theory all data about all stolen mobile phones should be distributed to all EIRs in the world through a Central EIR. It is clear, however, that there are some countries where this is not in operation. The EIR data does not have to change in real time, which means that this function can be less distributed than the function of the HLR. The EIR is a database that contains information about the identity of the mobile equipment that prevents calls from stolen, unauthorized or defective mobile stations. Some EIR also have the capability to log Handset attempts and store it in a log file.
centre supports the sending of multimedia messages (e.g., images, audio
, video
and their combinations) to (or from) MMS-enabled Handsets.
.
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.
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
and mobility management
Mobility management
Mobility management is one of the major functions of a GSM ora 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 delivered to them....
functions for mobile phones 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...
on the network of base stations
Base Station Subsystem
The base station subsystem 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...
. It is owned and deployed by mobile phone operators and allows mobile devices to communicate with each other and telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
s in the wider Public Switched Telephone Network or (PSTN)
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
. 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
Core network
A core network, or network core, is the central part of a telecommunication network that provides various services to customers who are connected by the access network. One of the main functions is to route telephone calls across the PSTN....
, used for traditional GSM services
GSM services
GSM services are a standard collection of applications and features available to mobile phone subscribers all over the world. The GSM standards are defined by the 3GPP collaboration and implemented in hardware and software by equipment manufacturers and mobile phone operators...
such as voice calls, SMS
Short message service
Short Message Service is a text messaging service component of phone, web, or mobile communication systems, using standardized communications protocols that allow the exchange of short text messages between fixed line or mobile phone devices...
, and circuit switched data
Circuit Switched Data
Circuit Switched Data is the original form of data transmission developed for the time division multiple access -based mobile phone systems like Global System for Mobile Communications...
calls. It was extended with an overlay architecture to provide packet-switched data services known as the GPRS core network
GPRS Core Network
The GPRS core network is the central part of the General Packet Radio Service which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet...
. This allows mobile phones to have access to services such as WAP
Wireless Application Protocol
Wireless Application Protocol is a technical standard for accessing information over a mobile wireless network.A WAP browser is a web browser for mobile devices such as mobile phones that uses the protocol.Before the introduction of WAP, mobile service providers had limited opportunities to offer...
, MMS
Multimedia Messaging Service
Multimedia Messaging Service, or MMS, is a standard way to send messages that include multimedia content to and from mobile phones. It extends the core SMS capability that allowed exchange of text messages only up to 160 characters in length.The most popular use is to send photographs from...
, and the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
.
All mobile phones manufactured today have both circuit and packet based services, so most operators have a GPRS network in addition to the standard GSM core network.
Description
The mobile switching center (MSC) is the primary service delivery node for GSM/CDMA, responsible for routingRouting in the PSTN
Routing in the PSTN is the process used to route telephone calls across the public switched telephone network. This process is the same whether the call is made between two phones in the same locality, or across two different continents....
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 pre-paid account monitoring.
In the GSM mobile phone system, in contrast with earlier analogue services, fax and data information is sent directly digitally encoded to the MSC. Only at the MSC is this re-coded into an "analogue" signal (although actually this will almost certainly mean sound encoded digitally as PCM
Pulse-code modulation
Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...
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 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 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 BSS
Base Station Subsystem
The base station subsystem 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...
s 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 VLR associated with this MSC will have 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 centre server
Mobile switching centre server
The Mobile Switching Centre Server, or MSC Server abbreviated MSS, is a 3G 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 implemented support for GSM networks in the MSS...
is a part of the redesigned MSC concept starting from 3GPP Release 4.
Mobile switching centre server (MSCS)
The mobile switching centre server is a soft-switch variant of the mobile switching centre, which provides circuit-switched calling, mobility management, and GSM services to the mobile phones roamingRoaming
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...
within the area that it serves. MSS functionality enables split between control (signalling) and user plane (bearer in network element called as media gateway/MG), which guarantees better placement of network elements within the network.
MSS and MGW media gateway
Media gateway
A Media gateway is a translation device or service that converts digital media streams between disparate telecommunications networks such as PSTN, SS7, Next Generation Networks or PBX...
makes it possible to cross-connect circuit switched calls switched by using IP, ATM AAL2 as well as TDM. More information is available in 3GPP TS 23.205.
Other GSM core network elements connected to the MSC
The MSC connects to the following elements:- The home location register (HLR) for obtaining data about the SIMSubscriber Identity ModuleA 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...
and mobile services ISDN number (MSISDN; i.e., the telephone number). - The base station subsystemBase Station SubsystemThe base station subsystem 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...
(BSS) which handles the radio communication with 2G2G2G is short for second-generation wireless telephone technology. Second generation 2G cellular telecom networks were commercially launched on the GSM standard in Finland by Radiolinja in 1991...
and 2.5G mobile phones. - The UMTS terrestrial radio access networkUtranUtran is a census town in Surat district in the Indian state of Gujarat.-Geography:Utran is located at . It has an average elevation of 12 metres .-Demographics:...
(UTRAN) which handles the radio communication with 3G3G3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...
mobile phones. - The visitor location register (VLR) for determining where other mobile subscribers are located.
- Other MSCs for procedures such as handover.
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 centreSMSC* Seoul Metro * Short message service center* Smart Mixed-Signal Connectivity...
(SMSC) and vice versa. - Arranging handovers from BSC to BSC.
- Carrying out handovers from this MSC to another.
- Supporting supplementary services 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 networkPublic land mobile network
A public land mobile network is a regulatory term in telecommunications. A PLMN is a network that is established and operated by an administration or by a recognized operating agency for the specific purpose of providing land mobile telecommunications services to the public.A PLMN is identified...
(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 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.
The next important items of data associated with the SIM are the MSISDNs, which are the telephone number
Telephone number
A telephone number or phone number is a sequence of digits used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator...
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
Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...
and data calls. Each MSISDN is also a primary key to the HLR record. The HLR data is stored for as long as a subscriber remains with the mobile phone operator.
MSISDN is not a distinguishable parameter in case of ported numbers. Instead, LRN and MSISDN combine to form a unique distinguishable parameter.
Examples of other data stored in the HLR against an IMSI record is:
- GSM services that the subscriber has requested or been given.
- GPRS settings to allow the subscriber to access packet services.
- Current location of subscriber (VLR and serving GPRS support node/SGSN).
- Call divertCall forwardingCall forwarding , in telephony, is a feature on some telephone networks allowing an incoming call to a called party to be redirected to a third party. For example, the third party may be a mobile telephone, voicemail box or other telephone number where the desired called party is situated. It was...
settings applicable for each associated MSISDN.
The HLR is a system which directly receives and processes MAP
Mobile Application Part
The Mobile Application Part is an SS7 protocol which provides an application layer for the various nodes in GSM and UMTS mobile core networks and GPRS core networks to communicate with each other in order to provide services to mobile phone users...
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 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.
Description
The authentication centre (AuC) is a function to authenticateAuthentication
Authentication is the act of confirming the truth of an attribute of a datum or entity...
each SIM card 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 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.
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
Shared secret
In cryptography, a shared secret is a piece of data, known only to the parties involved, in a secure communication. The shared secret can be a password, a passphrase, a big number or an array of randomly chosen bytes....
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 (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 crack proof. Therefore a new set of security methods was designed for 3G phones.
A3 Algorithm is used to encrypt Global System for Mobile Communications (GSM) cellular communications. In practice, A3 and A8 algorithms are generally implemented together (known as A3/A8). An A3/A8 algorithm is implemented in Subscriber Identity Module (SIM) cards and in GSM network Authentication Centres. 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.
Description
The visitor location register is a database of the subscribers who have roamed into the jurisdiction of the MSC (Mobile Switching Center) which it serves. Each base stationBase Transceiver Station
A base transceiver station or cell site is a piece of equipment that facilitates wireless communication between user equipment and a network. UEs are devices like mobile phones , WLL phones, computers with wireless internet connectivity, WiFi and WiMAX gadgets etc...
in the network is served by exactly one VLR, 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 HLR, or collected from the MS (Mobile station
Mobile Station
The mobile station comprises all user equipment and software needed for communication with a mobile network.The mobile station refers to global system connected to the mobile network, i.e. mobile phone or mobile computer connected using a mobile broadband adapter. This is the terminology of 2G...
). 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.
Other GSM core network elements connected to the VLR
The VLR connects to the following elements:- The V-MSC to pass required data for its procedures; e.g., authentication or call setup.
- The HLR to request data for mobile phones attached to its serving area.
- Other VLRs to transfer temporary data concerning the mobile when they roam into new VLR areas. For example, the temporal mobile subscriber identity (TMSI).
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)
The equipment identity registerCentral Equipment Identity Register
The Central Equipment Identity Register is a database of the IMEI numbers of blacklisted handsets. If a device's IMEI number is listed on CEIR, it is not supposed to work on any service provider.A common usage of the CEIR is with stolen cellphones...
is often integrated to the HLR. The EIR keeps a list of mobile phones (identified by their IMEI) which are to be banned from the network or monitored. This is designed to allow tracking of stolen mobile phones. In theory all data about all stolen mobile phones should be distributed to all EIRs in the world through a Central EIR. It is clear, however, that there are some countries where this is not in operation. The EIR data does not have to change in real time, which means that this function can be less distributed than the function of the HLR. The EIR is a database that contains information about the identity of the mobile equipment that prevents calls from stolen, unauthorized or defective mobile stations. Some EIR also have the capability to log Handset attempts and store it in a log file.
Other support functions
Connected more or less directly to the GSM core network are many other functions.Billing centre (BC)
The billing centre 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.Short message service centre (SMSC)
The short message service centre supports the sending and reception of text messages.Multimedia messaging service centre (MMSC)
The multimedia messaging serviceMultimedia Messaging Service
Multimedia Messaging Service, or MMS, is a standard way to send messages that include multimedia content to and from mobile phones. It extends the core SMS capability that allowed exchange of text messages only up to 160 characters in length.The most popular use is to send photographs from...
centre supports the sending of multimedia messages (e.g., images, audio
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
, video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and their combinations) to (or from) MMS-enabled Handsets.
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 CALEACommunications Assistance for Law Enforcement Act
The Communications Assistance for Law Enforcement Act is a United States wiretapping law passed in 1994, during the presidency of Bill Clinton...
.
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 GPRS core networkGPRS Core NetworkThe GPRS core network is the central part of the General Packet Radio Service which allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet...
with the rest of the GSM core network. - Base station subsystemBase Station SubsystemThe base station subsystem 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...