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The GSM standard was developed by the Groupe SpecialMobile, which was an initiative of the Conference of European Post and Telecommunications (CEPT) administrations. …

The GSM standard was developed by the Groupe SpecialMobile, which was an initiative of the Conference of European Post and Telecommunications (CEPT) administrations.


The responsibility for GSM standardization now resides with the
Special Mobile Group (SMG) under the European Telecommunication Standard Institute (ETSI).
Fully digital system utilizing the 900MHz frequency band.
TDMA over radiocarriers(200 kHz carrier spacing)
8 full rate or 16 half rate TDMA channels per carrier
User/terminal authentication for fraud control
Encryption of speech and data transmissions over the radio path
Full international roaming capability
Low speed data services (upto 9.6kb/s)
Compatibility with ISDN for supplementary services
Support of short message services(SMS)
GSM supports a range of basic and supplementary services, and these services are defined analogous to those for ISDN(i.e.,bearer services, teleservices, and supplementary services).
The most important service supported by GSM is Telephony.
Other services derived from telephony included in the GSM specification are emergency calling and voice messaging.
Bearer services supported in GSM include various asynchronous and synchronous data services for information transfer.
Teleservices based on these bearer services include group 3 fax and short message service(SMS)
The data capabilities of GSM have now been enhanced to include high speed circiut-switched data(HSCSD) and general packet radio service (GPRS).
Call offering services  call forwarding
Call resrtiction services  call barring
Call waiting service
Call hold service
Multi party service  tele conferencing
Calling line presentation restriction services
Advice of charge service
Closed user group service
The GSM System comprises of  Base Transceiver Station (BTS), Base Station Controllers (BSC), Mobile Switching Centers (MSC), and set of registers (databases) to assist in mobility management and security functions.
All signaling between the MSC and the various registers (databases) as well as between the MSCs takes place using the Signaling System 7(SS7) network, with the application level messages using the Mobile Application Protocol (MAP) designed specifically for GSM.
The MAP protocol utilizes the lower layer functions from the SS7 protocol stack.

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  • 1. Telecom Tutorialswww.TempusTelcosys.com 1
  • 2. STANDARDIZATION & ARCHITECTURE2www.TempusTelcosys.com
  • 3.  The GSM standard was developed by the GroupeSpecialMobile, which was an initiative of the Conference ofEuropean Post and Telecommunications (CEPT)administrations. The responsibility for GSM standardization now resides withtheSpecial Mobile Group (SMG) under the EuropeanTelecommunication Standard Institute (ETSI).3www.TempusTelcosys.com
  • 4.  Fully digital system utilizing the 900MHz frequency band. TDMA over radiocarriers(200 kHz carrier spacing) 8 full rate or 16 half rate TDMA channels per carrier User/terminal authentication for fraud control Encryption of speech and data transmissions over the radiopath Full international roaming capability Low speed data services (upto 9.6kb/s) Compatibility with ISDN for supplementary services Support of short message services(SMS)4www.TempusTelcosys.com
  • 5.  GSM supports a range of basic and supplementary services,and these services are defined analogous to those forISDN(i.e.,bearer services, teleservices, and supplementaryservices). The most important service supported by GSM is Telephony. Other services derived from telephony included in the GSMspecification are emergency calling and voice messaging. Bearer services supported in GSM include variousasynchronous and synchronous data services for informationtransfer. Teleservices based on these bearer services include group 3fax and short message service(SMS) The data capabilities of GSM have now been enhanced toinclude high speed circiut-switched data(HSCSD) and generalpacket radio service (GPRS).5www.TempusTelcosys.com
  • 6.  Call offering services  call forwarding Call resrtiction services  call barring Call waiting service Call hold service Multi party service  tele conferencing Calling line presentation restriction services Advice of charge service Closed user group service6www.TempusTelcosys.com
  • 7.  The GSM System comprises of  Base Transceiver Station(BTS), Base Station Controllers (BSC), Mobile SwitchingCenters (MSC), and set of registers (databases) to assist inmobility management and security functions. All signaling between the MSC and the various registers(databases) as well as between the MSCs takes place usingthe Signaling System 7(SS7) network, with the applicationlevel messages using the Mobile Application Protocol (MAP)designed specifically for GSM. The MAP protocol utilizes the lower layer functions from theSS7 protocol stack.7www.TempusTelcosys.com
  • 8. HLR/ACVLRVLREIRPSTNMSC MSCBSCDFCBGEAbisBTSBTSBTSA8www.TempusTelcosys.com
  • 9.  The GSM mobile stations are portable radiotelephony unitsthat can be used on any GSM sysytem as vehicular andhandheld terminals. Power levels supported by the GSM mobile station currentlyrange from 0.8 to 8.0 W ,and power saving techniques areused on the air interface to extend battery life. At the time of manufacture, an international mobileequipment identity (IMEI),is programmed into the terminal. A subscriber identity module (SIM) is required to activate andoperate a GSM terminal. The SIM may be contained within theMS , or it may be a removable unit. The international mobile subscriber identity (IMSI) isprogrammed into the SIM at the time of service provisioning,along with the appropriate security parameters andalgorithms.9www.TempusTelcosys.com
  • 10.  The base station system comprises a base station controller(BSC) and one or more subtending base transceiver stations(BTS). The BSS is responsible for all functions related to the radioresource (channel) management. Range of functions performed by the BSS  Radio resource control Configuration of radio channels Selection, allocation and deallocation of radio channels Monitoring of radio channel busy/idle status Encryption of radio interface Frequency hopping and power control Assignment of frequency-hop sequence and start time Assignment of effective radiated power (ERP) values to mobilestations10www.TempusTelcosys.com
  • 11.  Handoff management Collect signal quality data from adjacent BSSs Analyze signal quality data and determine handoff need Keep MSC informed regarding handoff activity Digital signal processing Transcoding and rate adaption Channel coding and decoding11www.TempusTelcosys.com
  • 12.  The Mobile Switching Centre or MSC is a sophisticatedtelephone exchange which provides circuit-switched calling,mobility management, and GSM services to the mobilephones roaming within the area that it serves. This meansvoice, data and fax services, as well as SMS and call divert. There are various different names for MSCs in differentcontexts which reflects their complex role in the network, allof these terms though could refer to the same MSC, but doingdifferent things at different times. A Gateway MSC is the MSC that determines which visited MSCthe subscriber who is being called is currently located. It alsointerfaces with the Public Switched Telephone Network. Allmobile to mobile calls and PSTN to mobile calls are routedthrough a GMSC.12www.TempusTelcosys.com
  • 13.  The Visited MSC is the MSC where a customer is currentlylocated. The VLR associated with this MSC will have thesubscribers data in it. The Anchor MSC is the MSC from which a handover has beeninitiated. The Target MSC is the MSC toward which a Handover shouldtake place13www.TempusTelcosys.com
  • 14.  The Home Location Register or HLR is a central database thatcontains details of each mobile phone subscriber that isauthorized to use the GSM core network. There is one HLR in one Public Land Mobile Network. HLR is asingle database but can be maintained as separate databaseswhen the data to be stored is more than the capacity. More precisely, the HLR stores details of every SIM cardissued by the mobile phone operator. Each SIM has a uniqueidentifier called an IMSI which is one of the primary keys toeach HLR record. The next important items of data associated with the SIM arethe telephone numbers used to make and receive calls to themobile phone, known as MSISDNs. The main MSISDN is thenumber used for making and receiving voice calls and SMS,but it is possible for a SIM to have other secondary MSISDNsassociated with it for fax and data calls. Each MSISDN is also aprimary key to the HLR record.14www.TempusTelcosys.com
  • 15.  Examples of other data stored in the HLR in a SIM record is: GSM services that the subscriber has requested or been given GPRS settings to allow the subscriber to access packetservices Current Location of subscriber (VLR and SGSN) Call divert settings applicable for each associated MSISDN. The HLR data is stored for as long as a subscriber remainswith the mobile phone operator. The HLR is a system which directly receives and processesMAP transactions and messages. If the HLR fails, then themobile network is effectively disabled as it is the HLR whichmanages the Location Updates as mobile phones roamaround.15www.TempusTelcosys.com
  • 16.  Visitor Location Register (VLR) is a database - part of the GSMmobile phone system - which stores information about all themobiles that are currently under the jurisdiction of the MSC(Mobile Switching Center) which it serves. Of all the information it stores about each MS (MobileStation), the most important is the current LAI (Location AreaIdentity) which identifies under which BSC (Base StationController) the MS is currently present. This information isvital in the call setup process. Whenever an MSC detects a new MS in its network, in additionto creating a new record in the VLR, it also updates the HLR ofthe mobile subscriber, apprising it of the new location of thatMS.16www.TempusTelcosys.com
  • 17.  When mobile equipment is stolen or lost, the operator orowner will typically contact the Central Equipment IdentityRegister (CEIR) which blacklists the device in all operatorswitches so that it will in effect become unusable, makingtheft of mobile equipment a useless business. The IMEI number is not supposed to be easy to change,making the CEIR blacklisting effective. However this is notalways the case: IMEI may be easy to change with specialtools and operators may even flatly ignore the CEIR blacklist.17www.TempusTelcosys.com
  • 18.  The Authentication Centre or AUC is a function to authenticate eachSIM card that attempts to connect to the GSM core network (typicallywhen the phone is powered on).An encryption key is also generatedthat is subsequently used to encrypt all wireless communications(voice, SMS, etc.) between the mobile phone and the GSM corenetwork. If the authentication fails, then no services are possible from thatparticular combination of SIM card and mobile phone operatorattempted. The AUC does not engage directly in the authentication process, butinstead generates data known as triplets for the MSC to use duringthe procedure. The security of the process depends upon a sharedsecret between the AUC and the SIM called the Ki. The Ki is securelyburned into the SIM during manufacture and is also securelyreplicated onto the AUC. This Ki is never transmitted between theAUC and SIM, but is combined with the IMSI to produce achallenge/response for identification purposes and an encryptionkey called Kc for use in over the air communications.18www.TempusTelcosys.com