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.



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.



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.



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



Telitphones Thurayaphones

Toshibaphones Vertuphones

VKMobilephones WNDphones

XCutephones

GSMEnabledPhones

gsm - quick guide

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