Storeandforwardservicesbasedoncellularnetworkdevelopment原文来源:WilliamEnckPatrickTraynorPatrickMcDanielandThomasLaPorta;SystemsandInternetinfrastructureSecurityLaboratoryDepartmentofComputerScienceandEngineering;ThePennsylvaniaStateUniversityPark,PA168021．SMS/CELLULARNETWORKOVERVIEWThissectionoffersasimplifiedviewofanSMSmessagetraversingaGSM-basedsystemfromsubmissiontodelivery.TheseproceduresaresimilarinothercellularnetworksincludingCDMA.1.1SubmittingaMessageTherearetwomethodsofsendingatextmessagetoamobiledevice-viaanothermobiledeviceorthroughavarietyofExternalShortMessagingEntities(ESMEs).ESMEsincludealargenumberofdiversedevicesandinterfacesrangingfromemailandweb-basedmessagingportalsatserviceproviderwebsitestovoicemailservices,pagingsystemsandsoftwareapplications.WhetherthesesystemsconnecttothemobilephonenetworkviatheInternetorspecificdedicatedchannels,messagesarefirstdeliveredtoaserverthathandlesSMStrafficknownastheShortMessagingServiceCenter(SMSC).AserviceprovidersupportingtextmessagingmusthaveatleastoneSMSCintheirnetwork.Duetotherisingpopularityofthisservice,however,itisbecomingincreasinglycommonforserviceproviderstosupportmultipleSMSCsinordertoincreasecapacity.Uponreceivingamessage,thecontentsofincomingpacketsareexaminedand,ifnecessary,convertedandcopiedintoSMSmessageformat.Atthispointinthesystem,messagesfromtheInternetbecomeindistinguishablefromthosethatoriginatedfrommobilephones.MessagesarethenplacedintoanSMSCqueueforforwarding.1.2RoutingaMessageTheSMSCneedstodeterminehowtoroutemessagestotheirtargetedmobiledevices.TheSMSCqueriesaHomeLocationRegister(HLR)database,whichservesasthepermanentrepositoryofuserdataandincludessubscriberinformation(e.g.callwaitingandtextmessaging),billingdata,availabilityofthetargeteduserandtheircurrentlocation.Throughinteractionwithothernetworkelements,theHLRdeterminestheroutinginformationforthedestinationdevice.IftheSMSCreceivesareplystatingthatthecurrentuserisunavailable,itstoresthetextmessageforlaterdelivery.Otherwise,theresponsewillcontaintheaddressoftheMobileSwitchingCenter(MSC)currentlyprovidingservice.Inadditiontocallrouting,MSCsareresponsibleforfacilitatingmobiledeviceauthentication,locationmanagementforattachedbasestations(BS),performinghandoffsandactingasgatewaystothePublicSwitchedTelephoneNetwork(PSTN).WhenatextmessagearrivesfromtheSMSC,theMSCfetchesinformationspecifictothetargetdevice.TheMSCqueriesadatabaseknownastheVisitorLocationRegister,whichreturnsalocalcopyofthetargeteddevice’sinformationwhenitisawayfromitsHLR.TheMSCthenforwardsthetextmessageontotheappropriatebasestationfortransmissionovertheairinterface.AdiagramofamobilephonenetworkisdepictedinFigure1.1,followedbyasimplifiedSMSmessageflowinFigure1.2.Figure1.1SMSNetworkFigure1.2SimplifiedexamplesofanSMSNetworkandmessageflow1.3WirelessDeliveryTheairinterfaceisdividedintotwoparts-theControlChannels(CCH)andTrafficChannels(TCH).TheCCHisfurtherdividedintotwotypesofchannels-theCommonCCHandDedicatedCCHs.TheCommonCCH,whichconsistsoflogicalchannelsincludingthePagingChannel(PCH)andRandomAccessChannel(RACH),isthemechanismusedbythebasestationtoinitiatethedeliveryofvoiceandSMSdata.Accordingly,allconnectedmobiledevicesareconstantlylisteningtotheCommonCCHforvoiceandSMSsignaling.ThebasestationsendsamessageonthePCHcontainingtheTemporaryMobileSubscriberID(TMSI)associatedwiththeenddest...