CSFB call flow - LTE

Leliwa Technical Bulletin

CSFBandSMSoSGs CSFBandSMSoSGs  CSFBandSMSoSGs

Date: Date: :

17.10.2009

Revision: Revision:

003/CAS/002

Author: Author: 

Jakub Bluszcz

1

. d e v r e s e R s t h g i R l l A . a w i l e L 0 1 0 2 © t h g i r y p o C

LeliwaTechnicalBulletinCSFBandSMSoSGs

Tableofcontents Tableofcontents

Topic Topic

Page Page

Introduction.....................................................................................................3 Architecture ....................................................................................................4 Co-existencewithIMS ....................................................................................5 Attachprocedure ............................................................................................7 TA/LAupdateprocedure.................................................................................9 Mobileoriginatingcall ...................................................................................11 MobileTerminatingCall ................................................................................13 SMS..............................................................................................................16 AcronymsandAbbreviations ........................................................................17 References ...................................................................................................18 Disclaimer.....................................................................................................19

2

CSFBandSMSoSLeliwaTechnicalBulletin

Introduction Introduction TheCSFallBack(CSFB)inEPSenablestheprovisioningofvoiceandother CS-domainservices(e.g.CSUDIvideo,LCS,USSD)byreuseofCS infrastructurewhentheUEisservedbyE-UTRAN.ACSFBenabledterminal, connectedtoE-UTRANmayuseGERANorUTRANtoconnecttothe CS-domain.ThisfunctionisonlyavailableincaseE-UTRANcoverageis overlappedbyeitherGERANcoverageorUTRANcoverage. 

CS domain service

GERAN /UTRAN

MSC

CS network

server

HO or cell reselection





Paging or Service Request

CS-domain service examples: • voice, • CS UDI video, • LCS, • USSD

SGs

MME

E-UTRAN

Figure1CSFallBack(CSFB) ThischapteralsodescribesthearchitecturerequiredforSMSoverSGs (MME–MSCinterface).TheMOSMSandMTSMSaresignalledoverSGs anddonotcauseanyCSFallbacktoGERAN/UTRANRATs,and consequentlydoesnotrequireanyoverlappedGERAN/UTRANcoverage.

HSS

MSC server

SMS-IWMSC/ SMS-GMSC

SMS-SC

SMS SGs

E-UTRAN

MME Figure2SMSoverSGs

3


Architecture Architecture TheCSFBandSMSoverSGsinEPSfunctionisrealizedbyusingtheSGs interfacemechanismbetweentheMSCServerandtheMME.

GERAN

MSC server Gs

UTRAN

SGSN

Sv

SGs

S3

E-UTRAN

MME

Figure3CSFallbackandSMSoverSGsarchitecture SGsisaninterfacebetweentheMMEandMSCserver.Itisusedforthe SGs MobilityManagement(MM)andpagingproceduresbetweenEPSandCS domain,andisbasedontheGs(VLR-SGSN)interfaceprocedures.TheSGs referencepointisalsousedforthedeliveryofbothMobileOriginatingand MobileTerminatingSMS(MO-SMSandMT-SMS). S3 S3isaninterfacebetweenMMEandSGSN.Ithasadditionalfunctionalityto supportCSFBwithISR.

Protocolstack Protocolstack

MME

MSC server

SGsAP

SGsAP

SCTP

SCTP

IP

IP

L2

L2

L1

L1

Figure4SGsprotocolstack

4


SGsApplicationPart(SGsAP)protocolisusedtoconnectanMMEtoan MSCServer.SGsAPisbasedontheBSSAP+protocol,usedearlieronGs (SGSN-VLR)interface. StreamControlTransmissionProtocol(SCTP)transferssignallingmessages.

CoCo-existencewithIMS existencewithIMS ForUEoriginatingcalls,theUEperformsaccessdomainselection.The servicedomainselectionfunctionalitydecideswhetherthecallisservicedin theCSdomainortheIMS.Servicedomainselectionfunctionalitymaytake intoaccountfororiginatingcallswhethertheuserisroamingornot,user preferences,servicesubscriptionandoperatorpolicy.IftheUEisconfigured forVoiceoverIMS,theservicedomainselectionfunctionalitytakesthe‘IMS voiceoverPSsessionsupportedindication’intoaccountandshouldonly initiateIMSvoicecalls(withthevoicebearerinthePSdomain)usingthe RATwherethe‘IMSvoiceoverPSsessionsupportedindication’appliesand indicatessupport.The"IMSvoiceoverPSsessionsupportedindication" appliestoE-UTRANwhenreceivedinE-UTRAN,andappliestoUTRAN wheneitherreceivedinGERANorUTRAN.

IMS voice over PS session supported indication

Attach accept / RAU Accept

SGSN

IMS voice over PS session supported indication

Attach accept / TAU Accept

MME

EPS attach result: EPS only / combined EPS/IMSI attach Additional result: - / CSFB not preferred / SMS only Figure5IMSvoiceoverPSsessionsupportedindication

5


Toallowforappropriatedomainselection,theCSFBandIMScapableUEin E-UTRANcanbeprovisionwiththeHPLMNoperatorpreferencesonhowa CSFB/IMSenabledUEissupposedtohandleviceservices: •

•

•

•

CSVoiceonly:theUEdoesnotattempttoinitiatevoicesessionsover CSVoiceonly IMSusingaPSbearer.TheUEattemptscombinedEPS/IMSIattach. CSVoicepreferred,IMSPSVoiceassecondary:theUEtries CSVoicepreferred,IMSPSVoiceassecondary preferablytousetheCSdomaintooriginateandterminatevoice calls.TheUEattemptscombinedEPS/IMSIattachandifcombined EPS/IMSIattachfailsfortheCSdomainorsucceedswithanSMS onlyindicationorsucceedswithaCSFBNotPreferredindication,the UEattemptsvoiceoverIMS. IMSPSVoicepreferred,CSVoiceassecondary IMSPSVoicepreferred,CSVoiceassecondary:theUEtries icepreferred,CSVoiceassecondary preferablytouseIMStooriginateandterminatevoicesessions.Ifthe UEfailstouseIMSforvoicee.g.dueto‘IMSvoiceoverPSsession supportedindication’indicatesvoiceisnotsupported,thenthe servicesareprovidedusingCSdomain.TheUEcaneitherperform combinedEPS/IMSIattachorEPSattachwhenattachingto E-UTRAN. IMSPSVoiceonly:theUEdoesnotattemptcombinedEPS/IMSI IMSPSVoiceonly attach(tosupportvoiceservices)andperformIMSregistration indicatingsupportforvoice.

ACSFB/IMSenabledUEmaybehaveineithera‘Voicecentric’or‘Data centric’way: •

UEactingina‘Voicecentric Voicecentric’wayalwaystriestoensurethatVoice Voicecentric serviceispossible.ACSFB/IMSenabledUEactingina‘Voice centric’waythatcannotobtainIMSvoiceoverPSsessionservice, selectsacellofanyRATthatprovidesaccesstotheCSdomain.In thiscase,whenCSFBisnotsupportedinthenetwork,theUEcamps onlyonRATsthatprovidesaccesstotheCSdomain(e.g.GERAN andUTRAN)anddisableE-UTRANcapability. UponreceivingcombinedEPS/IMSIattachacceptwith‘SMSonly’ indicationorwith‘CSFBNotPreferred’indication,avoicecentricUE thatfailstouseIMSreselectstoanotherRAT.

•

UEactingina‘Datacentric Datacentric’wayalwaystriestoensureitgetsPSdata Datacentric connectivity,e.g.theUEstaysinthecurrentRATforPSdata connectivityevenwhenvoiceserviceisnotobtained.ACSFB/IMS enabledUEactingina‘Datacentric’waythatcannotobtainIMSvoice overPSsessionserviceinEPS,continuestostayinEPSevenwhen theEPSdoesnotsupportCSFB. UponreceivingcombinedEPS/IMSIattachacceptwith‘SMSonly’ indication,adatacentricUEstaysinthecurrentRAT.

6


UponreceivingcombinedEPS/IMSIattachacceptwith‘CSFBNot Preferred’indication,adatacentricstaysinthecurrentRATandis allowedtouseCSFB.

• CS Voice only • CS Voice preferred, IMS PS Voice as secondary • IMS PS Voice preferred, CS Voice as secondary • IMS PS Voice only

• Voice centric • Data centric Figure6UEconfiguration(domainselection)

SMSoverIP SMSoverIP IfaUEisconfiguredtouseSMSoverIPservicesitshall,ifregisteredtoIMS, sendSMSoverIMS,evenifitisEPS/IMSIattached. Thehomeoperatorisabletoactivate/deactivatetheUEconfigurationtouse SMSoverIPbymeansofdevicemanagementinordertoallowalignment withHPLMNsupportofSMSoverIP.

Attachprocedure Attachprocedure TheattachprocedurefortheCSfallbackandSMSoverSGsinEPSis realizedbasedonthecombinedGPRS/IMSIAttachprocedurespecified earlierfortheGsinterface.

7


MME

MSC/VLR

HSS

 Attach Request 

Security procedures, registration and bearer establishment as in ordinary attach procedure. 

VLR number derivation  Location Update Req. 

SGs association creation 

 Attach Accept

Location Update in CS domain

 Location Update Accept

Figure7Attachprocedure TheUEinitiatestheattachprocedurebythetransmissionofanAttach

Request.messagetotheMME.TheAttachTypeparameterindicatesthatthe UErequestsacombinedEPS/IMSIattachandinformsthenetworkthatthe UEiscapableandconfiguredtouseCSfallback.IftheUEneedsSMS servicebutnotCSFB,theUEincludesan‘SMS-only’indication. Securityprocedures,registrationanddefaultbearerestablishmentasin

ordinaryEPSAttachprocedure. TheMMEallocatesadefaultLAI,whichisconfiguredontheMMEand

maytakeintoaccountthecurrentTAIand/orE-CGIandwhethertheIMSI attachisforbothCSFBandSMS,orforSMSonly.TheMMEderivesaVLR numberbasedontheallocatedLAIandIMSI.TheMMEstartsthelocation updateproceduretowardsthenewMSC/VLRuponreceiptofthesubscriber datafromtheHSSinstep. TheMMEsendsaLocationUpdateRequest(newLAI,IMSI,MMEIP

address,LocationUpdateType)messagetotheVLR. TheVLRcreatesanassociationwiththeMMEbystoringMMEaddress. TheVLRperformsLocationUpdatingprocedureinCSdomain. TheVLRrespondswithLocationUpdateAccept(TMSI)totheMME. TheEPSAttachprocedureiscompleted.AttachAcceptmessageincludes

LAIandTMSI.TheexistenceofLAIandTMSIindicatessuccessfulattachto CSdomain. IftheUErequestscombinedEPS/IMSIAttachRequestwithoutthe ‘SMS-only’indication,andifthenetworksupportsonlySMSoverSGs,the networkperformstheIMSIattachandtheMMEindicatesintheAttachAccept messagethattheIMSIattachisforSMSonly. WhenthenetworkacceptsacombinedEPS/IMSIattachwithoutlimitingto ‘SMS-only’,thenetworkmayprovidea‘CSFBNotPreferred’indicationtothe UE.

8


TA/LAu pdateprocedure procedure TA/LAupdate procedure ThecombinedTA/LAUpdateprocedurefortheCSFBandSMSoverSGsin EPSisrealizedbasedonthecombinedRA/LAUpdateprocedurespecifiedin earlierfortheGsinterface.

new MME

old MME

MSC/VLR

HSS

UE determines to perform TAU.



 TAU Request 

Security procedures, MME / S-GW reallocation, bearer modification as in ordinary TAU.  Location Update Request 

 TAU Request

Location Update in CS domain

 Location Update Accept

 TAU Complete

Figure8CombinedTA/LAupdate TheUEdetectsachangetoanewTAbydiscoveringthatitscurrentTAIis

notinthelistofTAIsthattheUEregisteredwiththenetwork. TheUEinitiatestheTAUprocedurebysendingaTAURequest.The

UpdateTypeindicatesthatthisisacombinedTrackingArea/LocationArea UpdateRequestoracombinedTrackingArea/LocationAreaUpdatewith IMSIattachRequest.IftheUEneedsSMSservicebutnotCSFB,theUE includean‘SMS-only’indicationinthecombinedTA/LAUpdateprocedure. Securityprocedures,possibleMMEandS-GWreallocationandbearer

modificationasinordinaryEPSTAUprocedure. IfthereisanassociatedVLRintheMMcontext,theVLRalsoneedstobe

updated.IftheassociationhastobeestablishedoriftheLAchanged,the newMMEsendsaLocationUpdateRequest(newLAI,IMSI,MMEIP address,LocationUpdateType)messagetotheVLR.NewLAIisdetermined intheMMEbasedonthereceivedGUTIfromtheUE.IfthisGUTIismapped fromaP-TMSI/RAI,theLAIisretrievedfromtheGUTIwithoutany modificationbytheMME.Otherwise,theMMEallocatesadefaultLAI,which isconfiguredontheMMEandmaytakeintoaccountthecurrentTAIorE-CGI andwhethertheIMSIattachisforbothCSFBandSMS,orforSMSonly.The MMEretrievesthecorrespondingVLRnumberfromthedeterminedLAI.If multipleMSC/VLRsservethisLAIanIMSIisusedtoretrievetheVLR numberfortheLAI..TheLocationUpdateTypeindicatesnormallocation update.

9


TheVLRperformsLocationUpdateprocedureinCSdomain. TheVLRrespondswithLocationUpdateAccept(TMSI)totheMME. TheMMEsendsaTAUAccept(LAI,TMSI)messagetotheUE.TheTMSI

isoptionaliftheVLRhasnotchanged.ThepresenceoftheLAIindicateto theUEthatitisIMSIattached.IftheUErequestscombinedTA/LAUpdate Requestwithoutthe‘SMS-only’indication,andifthenetworksupportsSGs forSMSonly,thenetworkperformstheIMSIattachandtheMMEindicatesin theTAUAcceptmessagethattheIMSIattachisforSMSonly. TheUEmaysendaTAUcompletemessagefortheTAUprocedureifthe

LAI/TMSIhasbeenchanged.

PeriodicTA/LAupdateprocedure PeriodicTA/LAupdateprocedure WhentheUEiscampedonE-UTRAN,periodicLAupdatesarenot performed,butperiodicTAupdatesareperformed.Inthiscase,anSGs associationisestablishedandtheMSC/VLRdisablesimplicitdetachfor EPS-attachedUEsandinsteadrelyontheMMEtoreceiveperiodicTA updates.

10


Mobileoriginatingcall Mobileoriginatingcall all TheprocedureforMTcallisillustratedinFig.9.

eNB/BSS/RNS

MME

MSC

SGSN

S-GW

 Extended Service Request  S1AP Request with CSFB ind.  Optional Measurement Report solicitation  PS HO / CCO optionally with NACC / connection release with redirection to GERAN/UTRAN  CM Service Request  CM Service Reject

if the MSC is changed and no implicit loc. upd.

LA update or combined LA/RA update  CS call establishment procedure  RA update (if necessary)

Figure9MOcall TheUEsendsanExtendedServiceRequest(CSFallbackIndicator)to

MME.CSFallbackIndicatorindicatesMMEtoperformCSFallback.TheUE onlytransmitsthisrequestifitisattachedtoCSdomain(withacombined EPS/IMSIAttach)andcannotinitiateanIMSvoicesession(becausee.g.the UEisnotIMSregisteredorIMSvoiceservicesarenotsupportedbythe servingIP-CAN,homePLMNorUE). TheMMEsendsanS1-APRequestmessagetoeNBthatincludesaCS

Fallbackindicator.ThismessageindicatestotheeNBthattheUEshouldbe movedtoUTRAN/GERAN. TheeNBmayoptionallysolicitameasurementreportfromtheUEto

determinethetargetGERAN/UTRANcelltowhichPShandoverwillbe performed. IftheUEandthenetworksupportinter-RAThandoverfromE-UTRANto

GERAN/UTRAN,theeNBtriggersPShandovertoaGERAN/UTRAN neighbourcellbysendingaHandoverRequiredmessagetotheMME. IftheUEandthenetworksupportinter-RATCellChangeOrder(CCO)to GERANandthetargetcellisGERAN,theeNBtriggersaninter-RATCCO (optionallywithNACC).

11


IftheUEorthenetworkdoesnotsupportinter-RAThandoverfromE-UTRAN toGERAN/UTRANnorinter-RATCCO,theeNBtriggersconnectionrelease withredirectiontoGERAN/UTRANinsteadofPSHOorCOO. TheUEestablishesCSsignallingconnectioninthetargetRATandsends

CMServiceRequestmessage.Thesimultaneoussupportofpacketdata bearersdependsonselectedRATandadditionalfeatureslikee.g.DTM. IncasetheMSCservingthe2G/3GtargetcellisdifferentfromtheMSC

thatservedtheUEwhilecampedonE-UTRAN,theMSCrejectstheservice request,ifimplicitlocationupdateisnotperformed.TheCMServiceReject triggerstheUEtoperformaLocationAreaUpdateasfollows: •

•

IfthetargetsystemoperatesinNetworkModeofOperation(NMO)I theUEperformsacombinedRA/LAupdate.Inthiscase,theSGSN establishesaGsassociationwiththeMSC/VLR,whichreplacesthe SGsassociationwiththeMME. IfthetargetsystemoperatesinNMOIIorIIItheUEperformsaLA updatetowardstheMSC.Inthiscase,theMSCreleasestheSGs associationwiththeMME.

TheUEinitiatestheCScallestablishmentprocedure. TheUEmaytriggertheRAupdateprocedurewhenthesendingofuplink

packetdataispossible.

12


MobileTerminatingCall MobileTerminatingCall TheprocedureforMTcallisillustratedinFig.10.

eNB/BSS/RNS

MME

 CS page

MSC

SGSN

S-GW

 IAM

 Extended Service Request  S1AP Request / S1AP Initial UE Context Setup

 Optional Measurement Report solicitation  PS HO / CCO optionally with NACC / connection release with redirection to GERAN/UTRAN 

LA update or combined LA/RA update  Paging Response  Connection Release / Reject

if the MSC is changed

LA update or combined LA/RA update and Roaming Retry for CSFB 

CS connection establishment

Figure10MTcall TheMSCreceivesanincomingvoicecall. TheMMEreceivesaCSPaging(IMSI,VLRTMSI,LocationInformation,

optionalCallerLineIdentification))messagefromtheMSCoveraSGs interface.TheTMSI(orIMSI)receivedfromtheMSCisusedbytheMMEto findtheS-TMSIwhichisusedasthepagingaddressontheradiointerface. IftheUEisinIdlemodetheMMEpagestheUEinalltheTAs,theUEis registeredto.1 InactivemodetheMMEreusestheexistingconnectiontorelaytheCSPage totheUE. TheeNBforwardsthepagingmessagetotheUE.Themessagecontainsa suitableUEIdentity(i.e.S-TMSIorIMSI)andaCNDomainindicatorand CallerLineIdentificationifavailableandneeded. TheUEestablishesanRRCconnectionorreusestheexistingconnection

tosendanExtendedServiceRequest(CSFallbackIndicator,Rejector Accept)toMME.  1Thisproceduretakesplacebeforestep,immediatelyafterMSCreceivesMAP_PRNfromHSS,ifprepagingisdeployed.

13


MMEsendsS1APInitialUEContextSetuporS1APRequestmessageto

eNBthatincludesCSFBindicator.ThismessageindicatestotheeNBthat theUEshouldbemovedtoUTRAN/GERAN. TheeNBmayoptionallysolicitameasurementreportfromtheUEto

determinethetargetGERAN/UTRANcelltowhichPShandoverwillbe performed. IftheUEandthenetworksupportinter-RAThandoverfromE-UTRANto

GERAN/UTRAN,theeNBtriggersPShandovertoaGERAN/UTRAN neighbourcellbysendingaHandoverRequiredmessagetotheMME. IftheUEandnetworksupportinter-RATCellChangeOrder(CCO)to GERANandthetargetcellisGERAN,theeNBtriggersaninter-RATCCO (optionallywithNACC). IftheUEorthenetworkdoesnotsupportinter-RAThandoverfromE-UTRAN toGERAN/UTRANnorinter-RATCCO,theeNBtriggersconnectionrelease withredirectiontoGERAN/UTRANinsteadofPSHOorCOO. IftheUEobtainsLA/RAinformationofthenewUTRAN/GERANcell(e.g.

basedonthesysteminformationorredirectioninfo)andtheLA/RAofthe newcellisdifferentfromtheonestoredintheUE,itperformsaLocationArea UpdateoraCombinedRA/LAprocedureifthetargetsystemoperatesin NMOI TheUEestablishesCSsignallingconnectioninthetargetRATandsends PagingResponsemessage2.Thesimultaneoussupportofpacketdata

bearersdependsonselectedRATandadditionalfeatureslikee.g.DTM. IftheMSCthatreceivesthePagingResponseisdifferentfromtheMSC

thatsentthepagingrequestandiftheLocationAreaUpdate/Combined RA/LAUpdatewasnotperformedinstep,theMSCrejectsthepage responsebyreleasingtheA/Iu-csconnection.TheBSC/RNCinturnreleases thesignallingconnectionforCSdomain.Thesignallingconnectionrelease triggerstheUEtoperformaLAupdateorCombinedRA/LAupdate. TheLAupdatetriggerstheRoamingRetryforCSFallbackprocedure, describedinthenextsection. describedinthenextsection. IncasetheMSCservingthe2G/3GcellisthesameastheMSCthat

servedtheUEwhilecampedonLTE,itshallstopthepagingresponsetimer andestablishtheCSconnection.

 2MSCshouldbepreparedtoreceiveapagingresponseafterarelativelylongtimefromwhentheCS Pagingwassent.TheBSSshouldbepreparedtoreceiveaPagingResponseevenwhenthe correspondingPagingRequesthasnotbeensentbythisBSS.

14


MTRoamingRetry MTRoamingRetryCall RoamingRetryCall Call MTRoamingRetryCallappliestoaMTcallwhilethecalledmobileis simultaneouslymovingfromanoldtoanewMSC,iftheGMSC,theHLRand theoldterminatingVMSCsupporttheMTRoamingRetryprocedure. Inthatcase,uponreceiptofanISUPIAMmessagewhichwaspreceededby aMAPCancelLocationprocedure,theoldVMSCinstructstheGMSCto resumeterminatingcallprocedurebysendingaMAPResumeCallHandling (RCH)message.TheGMSCthenreleasestheISUPconnectiontotheold VMSC,terminateanyopenCAPdialogue,andretrytheterminatingcallsetup towardsthenewMSCbysendinganadditionalSRItotheHLR.Thissecond SRIrequestleadstoobtainingaroamingnumberfromthenewMSCtowards whichthecallcanthenbedelivered(possiblyafternewCAMELinteractions). ThesimilarprocedureisusedforRoamingRetryforCSfallback.Thereare onlytwodifferencesinthisprocedurecomparedtotheMobileTerminating RoamingRetryCallproceduredescribedearlier.Thefirstdifferenceisthat thepagingmessagetriggerstheCSfallbackincludingalocationupdatein thenewRAT.ThisfunctionalityisalreadysupportedintheCSfallbackflows forterminatingcallsandnoadditionalfunctionalityisneeded.Thesecond differenceisthattheUEmaysendapageresponsemessageafterreceiving LocationUpdateAcceptmessage.ThenewMSCignoresorrejectsthepage responsemessage. MSC I A M H R C

SRI

IAM

GMSC

SRI

N R P

C L O C N A C

C S P A G

MME

HSS

C S F B

L U P

I A M

MSC

P L U t u p e S

Figure11RoamingRetryforCSfallback

15


SMS SMS TheproceduresforSMSoverSGsapplyonlyiftheUEisEPS/IMSIattached andtheCSaccessdomainischosenbytheUEand/orthehomePLMNfor deliveringshortmessages. SMSsupportisbasedonSGsinterfacebetweentheMMEandtheMSC ServeranduseofNASsignallingbetweentheUEandtheMME,i.e.noCS FallbackisperformedforSMS. TheSMSprotocolentitiesarereusedfromtheexistingMS/UEandMSC 2G/3Gimplementations.

HSS

MSC server

SMS-IWMSC/ SMS-GMSC SMS

SGs

E-UTRAN

MME Figure12SMSoverSGs

16

SMS-SC


AcronymsandAbbreviations AcronymsandAbbreviations 3G 3G 3GPP 3GPP AES AES CBC CBC CEK CEK CTR CTR DCF DCF DMP DMP DRM DRM EMS EMS GPRS GPRS HTTP HTTP IP IP IRDA IRDA ISO ISO MIME MIME MMS MMS OBEX OBEX ODRL ODRL OMA OMA PDA PDA PDCF PDCF PKI PKI PSS PSS REL REL ROAP ROAP RTSP RTSP SDP SDP SMS SMS URI URI USB USB WAP WAP

3-rd Generation 3rd Generation Partnership Project Advanced Encryption Standard Cipher Block Chaining Content Encryption Key Counter DRM Content Format Discrete Media Profile Digital Rights Management Element Management System General Packet Radio Service Hypertext Transfer Protocol Internet Protocol Infrared Data Association International Organization for Standardization Multipurpose Internet Mail Extensions Multimedia Messaging Service Object Exchange Open Digital Rights Language Open Mobile Alliance Personal Digital Assistant Packetized DRM Content Format Public Key Infrastructur Packet Streaming Service Rights Expression Language Rights Object Acquisition Protocol Real Time Streaming Protocol Session Description Protocol Short Message Service Uniform Resource Identifier Universal Serial Bus Wireless Application Protocol

17


References References Thissectioncontainsthelocationsofvariousspecifications,document referencesandusefulinformationwhereyoucanlearnmoreaboutthis subject.

18

[1]

23.272CircuitSwitched(CS)fallbackinEvolvedPacketSystem (EPS);Stage2

[2]

23.221Architecturalrequirements

[3]

24.301Non-Access-Stratum(NAS)protocolforEvolvedPacket System(EPS);Stage3


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19

CSFB call flow - LTE

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