gsm - quick guide
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GSMQUICKGUIDE
GSMOVERVIEW
WhatisGSM?
IfyouareinEuropeorAsiaandusingamobilephone,thenmostprobablyyouareusingGSMtechnologyinyourmobilephone.
GSMstandsforGlobalSystemforMobileCommunication.Itisadigitalcellulartechnologyusedfortransmittingmobilevoiceanddataservices.
TheconceptofGSMemergedfromacellbasedmobileradiosystematBellLaboratoriesintheearly1970s.
GSMisthenameofastandardizationgroupestablishedin1982tocreateacommonEuropeanmobiletelephonestandard.
GSMisthemostwidelyacceptedstandardintelecommunicationsanditisimplementedglobally.
GSMisacircuitswitchedsystemthatdivideseach200kHzchannelintoeight25kHztimeslots.GSMoperatesonthemobilecommunicationbands900MHzand1800MHzinmostpartsoftheworld.IntheUS,GSMoperatesinthebands850MHzand1900MHz.
GSMownsamarketshareofmorethan70percentoftheworld'sdigitalcellularsubscribers.
GSMmakesuseofnarrowbandTimeDivisionMultipleAccess techniquefortransmittingsignals.
GSMwasdevelopedusingdigitaltechnology.Ithasanabilitytocarry64kbpsto120Mbpsofdatarates.
PresentlyGSMsupportsmorethanonebillionmobilesubscribersinmorethan210countriesthroughouttheworld.
GSMprovidesbasictoadvancedvoiceanddataservicesincludingroamingservice.RoamingistheabilitytouseyourGSMphonenumberinanotherGSMnetwork.
GSMdigitizesandcompressesdata,thensendsitdownthroughachannelwithtwootherstreamsofuserdata,eachinitsowntimeslot.
WhyGSM?
ListedbelowarethefeaturesofGSMthataccountforitspopularityandwideacceptance.
Improvedspectrumefficiency
Internationalroaming
Lowcostmobilesetsandbasestations
Highqualityspeech
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CompatibilitywithIntegratedServicesDigitalNetwork andothertelephonecompanyservices
Supportfornewservices
GSMHistory
ThefollowingtableshowssomeoftheimportanteventsintherolloutoftheGSMsystem.
Years Events
1982 ConferenceofEuropeanPostsandTelegraph establishesaGSMgrouptowidenthestandardsforapanEuropeancellularmobilesystem.
1985 Alistofrecommendationstobegeneratedbythegroupisaccepted.
1986 Executedfieldteststocheckthedifferentradiotechniquesrecommendedfortheairinterface.
1987 TimeDivisionMultipleAccess ischosenastheaccessmethod.TheinitialMemorandumof
Understanding issignedbytelecommunicationoperatorsrepresenting12countries.
1988 GSMsystemisvalidated.
1989 TheEuropeanTelecommunicationsStandardsInstitute wasgiventheresponsibilityoftheGSMspecifications.
1990 Phase1oftheGSMspecificationsisdelivered.
1991 CommerciallaunchoftheGSMserviceoccurs.TheDCS1800specificationsarefinalized.
1992 TheadditionofthecountriesthatsignedtheGSMMoUtakesplace.Coveragespreadstolargercitiesandairports.
1993 CoverageofmainroadsGSMservicesstartsoutsideEurope.
1994 Datatransmissioncapabilitieslaunched.Thenumberofnetworksrisesto69in43countriesbytheendof1994.
1995 Phase2oftheGSMspecificationsoccurs.Coverageisextendedtoruralareas.
1996 June:133networkin81countriesoperational.
1997 July:200networkin109countriesoperational,around44millionsubscribersworldwide.
1999 WirelessApplicationProtocol cameintoexistenceandbecameoperationalin130countrieswith260millionsubscribers.
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2000 GeneralPacketRadioService cameintoexistence.
2001 AsofMay2001,over550millionpeopleweresubscriberstomobiletelecommunications.
GSMARCHITECTURE
AGSMnetworkcomprisesofmanyfunctionalunits.Thesefunctionsandinterfacesareexplainedinthischapter.TheGSMnetworkcanbebroadlydividedinto:
TheMobileStation
TheBaseStationSubsystem
TheNetworkSwitchingSubsystem
TheOperationSupportSubsystem
GivenbelowisasimplepictorialviewoftheGSMarchitecture.
TheadditionalcomponentsoftheGSMarchitecturecompriseofdatabasesandmessagingsystemsfunctions:
HomeLocationRegister
VisitorLocationRegister
EquipmentIdentityRegister
AuthenticationCenter
SMSServingCenter
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GatewayMSC
ChargebackCenter
TranscoderandAdaptationUnit
ThefollowingdiagramshowstheGSMnetworkalongwiththeaddedelements:
TheMSandtheBSScommunicateacrosstheUminterface.Itisalsoknownastheairinterfaceortheradiolink.TheBSScommunicateswiththeNetworkServiceSwitching centeracrosstheAinterface.
GSMnetworkareas
InaGSMnetwork,thefollowingareasaredefined:
Cell:CellisthebasicserviceareaoneBTScoversonecell.EachcellisgivenaCellGlobalIdentity ,anumberthatuniquelyidentifiesthecell.
LocationArea:AgroupofcellsformaLocationArea .Thisistheareathatispagedwhenasubscribergetsanincomingcall.EachLAisassignedaLocationAreaIdentity .EachLAisservedbyoneormoreBSCs.
MSC/VLRServiceArea:TheareacoveredbyoneMSCiscalledtheMSC/VLRservicearea.
PLMN:TheareacoveredbyonenetworkoperatoriscalledthePublicLandMobileNetwork.APLMNcancontainoneormoreMSCs.
GSMSPECIFICATION
TherequirementsfordifferentPersonalCommunicationServices systemsdifferforeachPCSnetwork.VitalcharacteristicsoftheGSMspecificationarelistedbelow:
Modulation
Modulationistheprocessoftransformingtheinputdataintoasuitableformatforthetransmissionmedium.Thetransmitteddataisdemodulatedbacktoitsoriginalformatthereceivingend.TheGSMusesGaussianMinimumShiftKeying modulationmethod.
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AccessMethods
Radiospectrumbeingalimitedresourcethatisconsumedanddividedamongalltheusers,GSMdevisedacombinationofTDMA/FDMAasthemethodtodividethebandwidthamongtheusers.Inthisprocess,theFDMApartdividesthefrequencyofthetotal25MHzbandwidthinto124carrierfrequenciesof200kHzbandwidth.
EachBSisassignedwithoneormultiplefrequencies,andeachofthisfrequencyisdividedintoeighttimeslotsusingaTDMAscheme.Eachoftheseslotsareusedforbothtransmissionaswellasreceptionofdata.Theseslotsareseparatedbytimesothatamobileunitdoesnttransmitandreceivedataatthesametime.
TransmissionRate
ThetotalsymbolrateforGSMat1bitpersymbolinGMSKproduces270.833Ksymbols/second.Thegrosstransmissionrateofatimeslotis22.8Kbps.
GSMisadigitalsystemwithanovertheairbitrateof270kbps.
FrequencyBand
TheuplinkfrequencyrangespecifiedforGSMis933960MHz .Thedownlinkfrequencyband890915MHz .
ChannelSpacing
Channelspacingindicatesthespacingbetweenadjacentcarrierfrequencies.ForGSM,itis200kHz.
SpeechCoding
Forspeechcodingorprocessing,GSMusesLinearPredictiveCoding .Thistoolcompressesthebitrateandgivesanestimateofthespeechparameters.Whentheaudiosignalpassesthroughafilter,itmimicsthevocaltract.Here,thespeechisencodedat13kbps.
DuplexDistance
Duplexdistanceisthespacebetweentheuplinkanddownlinkfrequencies.TheduplexdistanceforGSMis80MHz,whereeachchannelhastwofrequenciesthatare80MHzapart.
Misc
Frameduration:4.615mS
DuplexTechnique:FrequencyDivisionDuplexing accessmodepreviouslyknownasWCDMA.
SpeechchannelsperRFchannel:8.
GSMADDRESSESANDIDENTIFIERS
GSMtreatstheusersandtheequipmentindifferentways.Phonenumbers,subscribers,andequipmentidentifiersaresomeoftheknownones.Therearemanyotheridentifiersthathavebeenwelldefined,whicharerequiredforthesubscribersmobilitymanagementandforaddressingtheremainingnetworkelements.VitaladdressesandidentifiersthatareusedinGSMareaddressedbelow.
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InternationalMobileStationEquipmentIdentity
TheInternationalMobileStationEquipmentIdentity looksmorelikeaserialnumberwhichdistinctivelyidentifiesamobilestationinternationally.Thisisallocatedbytheequipmentmanufacturerandregisteredbythenetworkoperator,whostoresitintheEntrepreneursinResidence
.BymeansofIMEI,onerecognizesobsolete,stolen,ornonfunctionalequipment.
FollowingarethepartsofIMEI:
TypeApprovalCode :6decimalplaces,centrallyassigned.
FinalAssemblyCode :6decimalplaces,assignedbythemanufacturer.
SerialNumber :6decimalplaces,assignedbythemanufacturer.
Spare :1decimalplace.
Thus,IMEI=TAC+FAC+SNR+SP.Ituniquelycharacterizesamobilestationandgivescluesaboutthemanufacturerandthedateofmanufacturing.
InternationalMobileSubscriberIdentity
EveryregistereduserhasanoriginalInternationalMobileSubscriberIdentity withavalidIMEIstoredintheirSubscriberIdentityModule .
IMSIcomprisesofthefollowingparts:
MobileCountryCode :3decimalplaces,internationallystandardized.
MobileNetworkCode :2decimalplaces,foruniqueidentificationofmobilenetworkwithinthecountry.
MobileSubscriberIdentificationNumber :Maximum10decimalplaces,identificationnumberofthesubscriberinthehomemobilenetwork.
MobileSubscriberISDNNumber
TheauthentictelephonenumberofamobilestationistheMobileSubscriberISDNNumber.BasedontheSIM,amobilestationcanhavemanyMSISDNs,aseachsubscriberisassigned
withaseparateMSISDNtotheirSIMrespectively.
ListedbelowisthestructurefollowedbyMSISDNcategories,astheyaredefinedbasedoninternationalISDNnumberplan:
CountryCode :Upto3decimalplaces.
NationalDestinationCode :Typically23decimalplaces.
SubscriberNumber :Maximum10decimalplaces.
MobileStationRoamingNumber
MobileStationRoamingNumber isaninterimlocationdependentISDNnumber,assignedtoamobilestationbyaregionallyresponsibleVisitorLocationRegister .UsingMSRN,theincomingcallsarechannelledtotheMS.
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TheMSRNhasthesamestructureastheMSISDN.
CountryCode :ofthevisitednetwork.
NationalDestinationCode :ofthevisitednetwork.
SubscriberNumber :inthecurrentmobilenetwork.
LocationAreaIdentity
WithinaPLMN,aLocationAreaidentifiesitsownauthenticLocationAreaIdentity .TheLAIhierarchyisbasedoninternationalstandardandstructuredinauniqueformatasmentionedbelow:
CountryCode :3decimalplaces.
MobileNetworkCode :2decimalplaces.
LocationAreaCode :maximum5decimalplacesormaximumtwice8bitscodedinhexadecimal .
TemporaryMobileSubscriberIdentity
TemporaryMobileSubscriberIdentity canbeassignedbytheVLR,whichisresponsibleforthecurrentlocationofasubscriber.TheTMSIneedstohaveonlylocalsignificanceintheareahandledbytheVLR.ThisisstoredonthenetworksideonlyintheVLRandisnotpassedtotheHomeLocationRegister .
Togetherwiththecurrentlocationarea,theTMSIidentifiesasubscriberuniquely.Itcancontainupto48bits.
LocalMobileSubscriberIdentity
EachmobilestationcanbeassignedwithaLocalMobileSubscriberIdentity ,whichisanoriginalkey,bytheVLR.Thiskeycanbeusedastheauxiliarysearchingkeyforeachmobilestationwithinitsregion.Itcanalsohelpacceleratethedatabaseaccess.AnLMSIisassignedifthemobilestationisregisteredwiththeVLRandsenttotheHLR.LMSIcomprisesoffouroctets .
CellIdentifier
UsingaCellIdentifier bits,theindividualcellsthatarewithinanLAcanberecognized.WhentheGlobalCellIdentity callsarecombined,thenitisuniquelydefined.
GSMOPERATIONS
OnceaMobileStationinitiatesacall,aseriesofeventstakesplace.AnalyzingtheseeventscangiveaninsightintotheoperationoftheGSMsystem.
MobilePhonetoPublicSwitchedTelephoneNetwork
WhenamobilesubscribermakesacalltoaPSTNtelephonesubscriber,thefollowingsequenceofeventstakesplace:
TheMSC/VLRreceivesthemessageofacallrequest.
TheMSC/VLRchecksifthemobilestationisauthorizedtoaccessthenetwork.Ifso,themobile
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stationisactivated.Ifthemobilestationisnotauthorized,thentheservicewillbedenied.
MSC/VLRanalyzesthenumberandinitiatesacallsetupwiththePSTN.
MSC/VLRasksthecorrespondingBSCtoallocateatrafficchannel .
TheBSCallocatesthetrafficchannelandpassestheinformationtothemobilestation.
Thecalledpartyanswersthecallandtheconversationtakesplace.
ThemobilestationkeepsontakingmeasurementsoftheradiochannelsinthepresentcellandtheneighbouringcellsandpassestheinformationtotheBSC.TheBSCdecidesifahandoverisrequired.Ifso,anewtrafficchannelisallocatedtothemobilestationandthehandovertakesplace.Ifhandoverisnotrequired,themobilestationcontinuestotransmitinthesamefrequency.
PSTNtoMobilePhone
WhenaPSTNsubscribercallsamobilestation,thefollowingsequenceofeventstakesplace:
TheGatewayMSCreceivesthecallandqueriestheHLRfortheinformationneededtoroutethecalltotheservingMSC/VLR.
TheGMSCroutesthecalltotheMSC/VLR.
TheMSCcheckstheVLRforthelocationareaoftheMS.
TheMSCcontactstheMSviatheBSCthroughabroadcastmessage,thatis,throughapagingrequest.
TheMSrespondstothepagerequest.
TheBSCallocatesatrafficchannelandsendsamessagetotheMStotunetothechannel.TheMSgeneratesaringingsignaland,afterthesubscriberanswers,thespeechconnectionisestablished.
Handover,ifrequired,takesplace,asdiscussedintheearliercase.
Totransmitthespeechovertheradiochannelinthestipulatedtime,theMScodesitattherateof13Kbps.TheBSCtranscodesthespeechto64KbpsandsendsitoveralandlinkoraradiolinktotheMSC.TheMSCthenforwardsthespeechdatatothePSTN.Inthereversedirection,thespeechisreceivedat64KbpsattheBSCandtheBSCtranscodesitto13Kbpsforradiotransmission.
GSMsupports9.6KbpsdatathatcanbechannelledinoneTDMAtimeslot.Tosupplyhigherdatarates,manyenhancementsweredonetotheGSMstandards .
GSMPROTOCOLSTACK
GSMarchitectureisalayeredmodelthatisdesignedtoallowcommunicationsbetweentwodifferentsystems.Thelowerlayersassuretheservicesoftheupperlayerprotocols.Eachlayerpassessuitablenotificationstoensurethetransmitteddatahasbeenformatted,transmitted,andreceivedaccurately.
TheGMSprotocolstacksdiagramisshownbelow:
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MSProtocols
Basedontheinterface,theGSMsignalingprotocolisassembledintothreegenerallayers:
Layer1:Thephysicallayer.Itusesthechannelstructuresovertheairinterface.
Layer2:Thedatalinklayer.AcrosstheUminterface,thedatalinklayerisamodifiedversionoftheLinkaccessprotocolfortheDchannel protocolusedinISDN,calledLinkaccessprotocolontheDmchannel .AcrosstheAinterface,theMessageTransferPart
,Layer2ofSS7isused.
Layer3:GSMsignallingprotocolsthirdlayerisdividedintothreesublayers:
RadioResourceManagement ,
MobilityManagement ,and
ConnectionManagement .
MStoBTSProtocols
TheRRlayeristhelowerlayerthatmanagesalink,bothradioandfixed,betweentheMSandtheMSC.Forthisformation,themaincomponentsinvolvedaretheMS,BSS,andMSC.TheresponsibilityoftheRRlayeristomanagetheRRsession,thetimewhenamobileisinadedicatedmode,andtheradiochannelsincludingtheallocationofdedicatedchannels.
TheMMlayerisstackedabovetheRRlayer.Ithandlesthefunctionsthatarisefromthemobilityofthesubscriber,aswellastheauthenticationandsecurityaspects.LocationmanagementisconcernedwiththeproceduresthatenablethesystemtoknowthecurrentlocationofapoweredonMSsothatincomingcallroutingcanbecompleted.
TheCMlayeristhetopmostlayeroftheGSMprotocolstack.ThislayerisresponsibleforCallControl,SupplementaryServiceManagement,andShortMessageServiceManagement.EachoftheseservicesaretreatedasindividuallayerwithintheCMlayer.OtherfunctionsoftheCCsublayerincludecallestablishment,selectionofthetypeofservice ,andcallrelease.
BSCProtocols
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TheBSCusesadifferentsetofprotocolsafterreceivingthedatafromtheBTS.TheAbisinterfaceisusedbetweentheBTSandBSC.Atthislevel,theradioresourcesatthelowerportionofLayer3arechangedfromtheRRtotheBaseTransceiverStationManagement .TheBTSmanagementlayerisarelayfunctionattheBTStotheBSC.
TheRRprotocolsareresponsiblefortheallocationandreallocationoftrafficchannelsbetweentheMSandtheBTS.Theseservicesincludecontrollingtheinitialaccesstothesystem,pagingforMTcalls,thehandoverofcallsbetweencellsites,powercontrol,andcalltermination.TheBSCstillhassomeradioresourcemanagementinplaceforthefrequencycoordination,frequencyallocation,andthemanagementoftheoverallnetworklayerfortheLayer2interfaces.
TotransitfromtheBSCtotheMSC,theBSSmobileapplicationpartorthedirectapplicationpartisused,andSS7protocolsisappliedbytherelay,sothattheMTP13canbeusedastheprimearchitecture.
MSCProtocols
AttheMSC,startingfromtheBSC,theinformationismappedacrosstheAinterfacetotheMTPLayers1through3.Here,BaseStationSystemManagementApplicationPart issaidtobetheequivalentsetofradioresources.TherelayprocessisfinishedbythelayersthatarestackedontopofLayer3protocols,theyareBSSMAP/DTAP,MM,andCM.Thiscompletestherelayprocess.Tofindandconnecttotheusersacrossthenetwork,MSCsinteractusingthecontrolsignallingnetwork.LocationregistersareincludedintheMSCdatabasestoassistintheroleofdetermininghowandwhetherconnectionsaretobemadetoroamingusers.
EachGSMMSuserisgivenaHLRthatinturncomprisesoftheuserslocationandsubscribedservices.VLRisaseparateregisterthatisusedtotrackthelocationofauser.WhentheusersmoveoutoftheHLRcoveredarea,theVLRisnotifiedbytheMStofindthelocationoftheuser.TheVLRinturn,withthehelpofthecontrolnetwork,signalstheHLRoftheMSsnewlocation.WiththehelpoflocationinformationcontainedintheusersHLR,theMTcallscanberoutedtotheuser.
GSMUSERSERVICES
GSMoffersmuchmorethanjustvoicetelephony.ContactyourlocalGSMnetworkoperatortothespecificservicesthatyoucanavail.
GSMoffersthreebasictypesofservices:
Telephonyservicesorteleservices
Dataservicesorbearerservices
Supplementaryservices
Teleservices
TheabilitiesofaBearerServiceareusedbyaTeleservicetotransportdata.Theseservicesarefurthertransitedinthefollowingways:
VoiceCalls
ThemostbasicTeleservicesupportedbyGSMistelephony.Thisincludesfullratespeechat13kbpsandemergencycalls,wherethenearestemergencyserviceproviderisnotifiedbydialingthreedigits.
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VideotextandFacsmile
AnothergroupofteleservicesincludesVideotextaccess,Teletextransmission,FacsimilealternatespeechandfacsimileGroup3,AutomaticfacsimileGroup,3etc.
ShortTextMessages
ShortMessagingService serviceisatextmessagingservicethatallowssendingandreceivingtextmessagesonyourGSMmobilephone.Inadditiontosimpletextmessages,othertextdataincludingnews,sports,financial,language,andlocationbaseddatacanalsobetransmitted.
BearerServices
DataservicesorBearerServicesareusedthroughaGSMphone.toreceiveandsenddataistheessentialbuildingblockleadingtowidespreadmobileInternetaccessandmobiledatatransfer.GSMcurrentlyhasadatatransferrateof9.6k.NewdevelopmentsthatwillpushupdatatransferratesforGSMusersareHSCSD andGPRS arenowavailable.
SupplementaryServices
Supplementaryservicesareadditionalservicesthatareprovidedinadditiontoteleservicesandbearerservices.Theseservicesincludecalleridentification,callforwarding,callwaiting,multipartyconversations,andbarringofoutgoing calls,amongothers.Abriefdescriptionofsupplementaryservicesisgivenhere:
Conferencing:Itallowsamobilesubscribertoestablishamultipartyconversation,i.e.,asimultaneousconversationbetweenthreeormoresubscriberstosetupaconferencecall.Thisserviceisonlyapplicabletonormaltelephony.
CallWaiting:Thisservicenotifiesamobilesubscriberofanincomingcallduringaconversation.Thesubscribercananswer,reject,orignoretheincomingcall.
CallHold:Thisserviceallowsasubscribertoputanincomingcallonholdandresumeafterawhile.Thecallholdserviceisapplicabletonormaltelephony.
CallForwarding:CallForwardingisusedtodivertcallsfromtheoriginalrecipienttoanothernumber.Itisnormallysetupbythesubscriberhimself.ItcanbeusedbythesubscribertodivertcallsfromtheMobileStationwhenthesubscriberisnotavailable,andsotoensurethatcallsarenotlost.
CallBarring:CallBarringisusefultorestrictcertaintypesofoutgoingcallssuchasISDorstopincomingcallsfromundesirednumbers.Callbarringisaflexibleservicethatenablesthesubscribertoconditionallybarcalls.
NumberIdentification:Therearefollowingsupplementaryservicesrelatedtonumberidentification:
CallingLineIdentificationPresentation:Thisservicedisplaysthetelephonenumberofthecallingpartyonyourscreen.
CallingLineIdentificationRestriction:Apersonnotwishingtheirnumbertobepresentedtootherssubscribestothisservice.
ConnectedLineIdentificationPresentation:Thisserviceisprovidedtogivethe
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callingpartythetelephonenumberofthepersontowhomtheyareconnected.Thisserviceisusefulinsituationssuchasforwarding'swherethenumberconnectedisnotthenumberdialled.
ConnectedLineIdentificationRestriction:Therearetimeswhenthepersoncalleddoesnotwishtohavetheirnumberpresentedandsotheywouldsubscribetothisperson.Normally,thisoverridesthepresentationservice.
MaliciousCallIdentification:Themaliciouscallidentificationservicewasprovidedtocombatthespreadofobsceneorannoyingcalls.Thevictimshouldsubscribetothisservice,andthentheycouldcauseknownmaliciouscallstobeidentifiedintheGSMnetwork,usingasimplecommand.
AdviceofCharge :Thisservicewasdesignedtogivethesubscriberanindicationofthecostoftheservicesastheyareused.Furthermore,thoseserviceproviderswhowishtoofferrentalservicestosubscriberswithouttheirownSIMcanalsoutilizethisserviceinaslightlydifferentform.AoCfordatacallsisprovidedonthebasisoftimemeasurements.
ClosedUserGroups :Thisserviceismeantforgroupsofsubscriberswhowishtocallonlyeachotherandnooneelse.
Unstructuredsupplementaryservicesdata :Thisallowsoperatordefinedindividualservices.
GSMSECURITYANDENCRYPTION
GSMisthemostsecuredcellulartelecommunicationssystemavailabletoday.GSMhasitssecuritymethodsstandardized.GSMmaintainsendtoendsecuritybyretainingtheconfidentialityofcallsandanonymityoftheGSMsubscriber.
Temporaryidentificationnumbersareassignedtothesubscribersnumbertomaintaintheprivacyoftheuser.Theprivacyofthecommunicationismaintainedbyapplyingencryptionalgorithmsandfrequencyhoppingthatcanbeenabledusingdigitalsystemsandsignalling.
ThischaptergivesanoutlineofthesecuritymeasuresimplementedforGSMsubscribers.
MobileStationAuthentication
TheGSMnetworkauthenticatestheidentityofthesubscriberthroughtheuseofachallengeresponsemechanism.A128bitRandomNumber issenttotheMS.TheMScomputesthe32bitSignedResponse basedontheencryptionoftheRANDwiththeauthenticationalgorithm usingtheindividualsubscriberauthenticationkey .UponreceivingtheSRESfromthesubscriber,theGSMnetworkrepeatsthecalculationtoverifytheidentityofthesubscriber.
Theindividualsubscriberauthenticationkey isnevertransmittedovertheradiochannel,asitispresentinthesubscriber'sSIM,aswellastheAUC,HLR,andVLRdatabases.IfthereceivedSRESagreeswiththecalculatedvalue,theMShasbeensuccessfullyauthenticatedandmaycontinue.Ifthevaluesdonotmatch,theconnectionisterminatedandanauthenticationfailureisindicatedtotheMS.
ThecalculationofthesignedresponseisprocessedwithintheSIM.Itprovidesenhancedsecurity,asconfidentialsubscriberinformationsuchastheIMSIortheindividualsubscriberauthenticationkeyisneverreleasedfromtheSIMduringtheauthenticationprocess.
SignallingandDataConfidentiality
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TheSIMcontainsthecipheringkeygeneratingalgorithm thatisusedtoproducethe64bitcipheringkey .Thiskeyiscomputedbyapplyingthesamerandomnumber usedintheauthenticationprocesstocipheringkeygeneratingalgorithm withtheindividualsubscriberauthenticationkey .
GSMprovidesanadditionallevelofsecuritybyhavingawaytochangethecipheringkey,makingthesystemmoreresistanttoeavesdropping.Thecipheringkeymaybechangedatregularintervalsasrequired.Asincaseoftheauthenticationprocess,thecomputationofthecipheringkey takesplaceinternallywithintheSIM.Therefore,sensitiveinformationsuchastheindividualsubscriberauthenticationkey isneverrevealedbytheSIM.
EncryptedvoiceanddatacommunicationsbetweentheMSandthenetworkisaccomplishedbyusingthecipheringalgorithmA5.EncryptedcommunicationisinitiatedbyacipheringmoderequestcommandfromtheGSMnetwork.Uponreceiptofthiscommand,themobilestationbeginsencryptionanddecryptionofdatausingthecipheringalgorithm andthecipheringkey .
SubscriberIdentityConfidentiality
Toensuresubscriberidentityconfidentiality,theTemporaryMobileSubscriberIdentity isused.Oncetheauthenticationandencryptionproceduresaredone,theTMSIissenttothemobilestation.Afterthereceipt,themobilestationresponds.TheTMSIisvalidinthelocationareainwhichitwasissued.Forcommunicationsoutsidethelocationarea,theLocationAreaIdentification isnecessaryinadditiontotheTMSI.
GSMBILLING
GSMserviceprovidersaredoingbillingbasedontheservicestheyareprovidingtotheircustomers.Alltheparametersaresimpleenoughtochargeacustomerfortheprovidedservices.
ThischapterprovidesanoverviewofthefrequentlyusedbillingtechniquesandparametersappliedtochargeaGSMsubscriber.
TelephonyService
Theseservicescanbechargedonpercallbasis.Thecallinitiatorhastopaythecharges,andtheincomingcallsarenowadaysfree.Acustomercanbechargedbasedondifferentparameterssuchas:
Internationalcallorlongdistancecall.
Localcall.
Callmadeduringpeakhours.
Callmadeduringnighttime.
Discountedcallduringweekends.
Callperminuteorpersecond.
Manymoreothercriteriacanbedesignedbyaserviceprovidertochargetheircustomers.
SMSService
Mostoftheserviceproviderschargetheircustomer'sSMSservicesbasedonthenumberoftextmessagessent.ThereareotherprimeSMSservicesavailablewhereserviceproviderschargemorethannormalSMScharge.TheseservicesarebeingavailedincollaborationofTelevisionNetworksorRadio
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NetworkstodemandSMSfromtheaudiences.
Mostofthetime,thechargesarepaidbytheSMSsenderbutforsomeserviceslikestocksandshareprices,mobilebankingfacilities,andleisurebookingservices,etc.therecipientoftheSMShastopayfortheservice.
GPRSServices
UsingGPRSservice,youcanbrowse,playgamesontheInternet,anddownloadmovies.Soaserviceproviderwillchargeyoubasedonthedatauploadedaswellasdatadownloadedonyourmobilephone.ThesechargeswillbebasedonperKiloBytedatadownloaded/uploaded.
AdditionalparametercouldbeaQoSprovidedtoyou.Ifyouwanttowatchamovie,thenalowQoSmayworkbecausesomedatalossmaybeacceptable,butifyouaredownloadingazipfile,thenasinglebytelosswillcorruptyourcompletedownloadedfile.
AnotherparametercouldbepeakandoffpeaktimetodownloadadatafileortobrowsetheInternet.
SupplementaryServices
Mostofthesupplementaryservicesarebeingprovidedbasedonmonthlyrentalorabsolutelyfree.Forexample,callwaiting,callforwarding,callingnumberidentification,andcallonholdareavailableatzerocost.
Callbarringisaservice,whichserviceprovidersusejusttorecovertheirdues,etc.,otherwisethisserviceisnotbeingusedbyanysubscriber.
Callconferencingserviceisaformofsimpletelephonecallwherethecustomersarechargedformultiplecallsmadeatatime.Noserviceproviderchargesextrachargeforthisservice.
ClosedUserGroup isverypopularandismainlybeingusedtogivespecialdiscountstotheusersiftheyaremakingcallstoaparticulardefinedgroupofsubscribers.
AdviceofCharge canbechargedbasedonnumberofqueriesmadebyasubscriber.
GSMMOBILEPHONES
GSMArenaisthebiggestsourceofinformationaboutthelatestGSMmobilephones.ThispageisbeingdisplayedhereasacourtesyofGSMArena.IfyouareplanningtobuyaGSMmobilephone,thenwesuggestyougothroughallthereviewcommentsandthendecidewhichphoneissuitableforyou.
Alcatelphones Amoiphones
Applephones Asusphones
Benefonphones BenQphones
BenQSiemensphones Birdphones
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BlackBerryphones Boschphones
Cheaphones Ericssonphones
Etenphones FujitsuSiemensphones
Gigabytephones Haierphones
HPphones HTCphones
imatephones Innostreamphones
Kyoceraphones LGphones
Maxonphones Mitacphones
Mitsubishiphones Motorolaphones
NECphones Neonodephones
Nokiaphones O2phones
Palmphones Panasonicphones
Pantechphones Philipsphones
Qtekphones Sagemphones
Samsungphones Sendophones
Sewonphones Sharpphones
Siemensphones Sonyphones
SonyEricssonphones Tel.Me.phones
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Telitphones Thurayaphones
Toshibaphones Vertuphones
VKMobilephones WNDphones
XCutephones
GSMEnabledPhones