Android Telephony Internals.docx
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Android Telephony Internals.docx
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AndroidTelephonyInternals
AndroidTelephonyInternals
The restofthischaptercoverstelephony-relatedclassesintheinternalspackagethatonlyPhoneAppuses, android.internal.telephony.Thispackageislayeredoveranimplementationoftelephonyinternalsforaparticulartelephonytechnology,suchasGSMorCDMA.Thatlayer,inturn,communicateswithaRadioInterfaceLayer(RIL)that isimplementedasadaemoninAndroid.
Figure15-1 showsthearchitectureoftheAndroidtelephonysystem.PhoneAppsupportsanIntentthatenablesotherapplicationstostartphonecalls.TheTelephonyManagerisavailablethroughListeners,asshownintheprevioussection.
Figure15-1.Layersoftelephonypackages
15.2.1.Inter-ProcessCommunicationandAIDLinthe android.internal.telephonyPackage
Many oftheinternalpackagesusetheremotemethodsfeaturediscussedin Section13.2.The TelephonyManager and PhoneStateListener classesrelyonthistocommunicatewithPhoneApp.The ServiceManager classisalsoused.
Tomarshalldataforremotemethods,thepackageincludesAIDLfiles.Forinstance,thefollowingAIDLcomesfrom IPhoneStateListener.aidl:
onewayinterfaceIPhoneStateListener{
voidonServiceStateChanged(inServiceStateserviceState);
voidonSignalStrengthChanged(intasu);
voidonMessageWaitingIndicatorChanged(booleanmwi);
voidonCallForwardingIndicatorChanged(booleancfi);
//weusebundlehereinsteadofCellLocationsoitcangettherightsubclass
voidonCellLocationChanged(inBundlelocation);
voidonCallStateChanged(intstate,StringincomingNumber);
voidonDataConnectionStateChanged(intstate);
voidonDataActivity(intdirection);
}
15.2.2.Theandroid.internal.telephonyPackage
ThispackagecontainstheclassesandinterfacesPhoneAppusestoprovideservicestootherapplicationsthatwanttostartphonecalls,andclassesthatdefineanAPItotheRIL.
PhoneApp,likeallpartsofAndroid,istheoreticallyreplaceable.IfyourapplicationneedstomodifytheclassesusedbyPhoneApp,yourapplicationwillprobablyhavetoreplaceormodifyPhoneApp,andshouldprovidethesameservicestootherapplications,usingtheclassesinthispackage.
ThedescriptionoftheseclassesshouldhelpyouunderstandhowAndroidinterfacestoamobileradio,andthecapabilitiesthatareexposed—andnotexposed—by PhoneApp tootherapplications.Thisisalargeandcomplexpackage,andacompleteunderstandingwillrequirereadingtheAndroidsourcecode.Thesedescriptionswillhelpyoufindwheretostartforyourpurposes:
ATParseEx
Extends RuntimeExceptionandisthrownbymethodsofthe ATResponseParser class.
ATResponseParser
Thisclassparses partoftheATcommandsyntaxusedtocommunicatewiththemobileradiohardwareinamobilehandset.Thisis,infact,acommandsyntaxverymuchliketheATcommandsyntaxusedbymodems,astandarddescribedinthe3GPPdocumentnumberTS27.007andrelatedspecifications.Thisprotocolforcontrollingmobileradiosiswidelyused.
Call
Thisclassisan abstractbaseclass.Otherclassesuseitasabasisforobjectsthatrepresentphonecallsandthestateofthosecalls.
CallerInfo
Thisclass holdsinformationaboutthepartythatoriginatedanincomingcall.ThisclassstartswithcallerIDinformationfromthemobilenetworkinterfaceandlooksupotherinformationaboutacallerinthedatabaseofcontacts.
CallerInfoAsyncQuery
Thisclass enablesasynchronousdatabasequeriesforinformationthatcouldbefoundaboutacallerbasedonthecallerIDinformation.
CallStateException
Theclass extendsExceptionandisthrownbymethodsthatmaintaincallstateincaseswherestateisinconsistent.
Connection
Thisclass isanabstractbaseclassusedbyotherclasses,andisabasisforobjectsthatrepresentconnectionsonthemobilenetworkandthestateoftheseconnections. Connection objectscanbeassociatedwitha Call object,buttheycanalsoexistindependently.ThedatainaConnection objectcanbeespeciallyusefulindiagnosingthereasonacallfailed.
DefaultPhoneNotifier
Thisclass implementsthePhoneNotifierinterfaceinordertoreceivenotificationsfroma Phone object.ItthenusestheAndroidservicesystemtocommunicatestatetoActivityinstancesthathaveregisteredtoreceivethosenotifications.Seethe Handler and Mailbox classesforinformationonhowtoreceivenotifications.
IPhoneStateListener
This interfacedefinesthesignaturesofmethodsanapplicationimplementstoreceivenotificationofcallstatechange,andchangestoforwardingandmessage-waitingstates.
IPhoneSubInfo
Thisinterface isusedtoobtainsubscriberinformation.
ITelephony
This interfacedefinestheinter-processinterfaceusedinTelephonyManagertoenableapplicationstocommunicatewithPhoneApp.
ITelephonyRegistry
This interfaceisthecallbackinterfacefromtheRILdaemon.
MmiCode
This interfacedefinescallbacksrelatedto"MMIcodes."Thesearespecialnumbersausercandialandkeysequencesthatausercanenterduringacalltoaccess,control,andadministersupplementaryservices,suchascallwaiting,callhold,etc.MMIcodesandrelatedfunctionalityaredescribedinthe3GPPdocumentnumberTS22.030.
Phone
This interfaceincludescallbacksandmethodsforaccessingthestateofamobilephone.
PhoneBase
This classisanabstractbaseclassthatimplementsthePhoneinterface.
PhoneFactory
This classcontainsmethodsusedtocreateinstancesofthe GSMPhone class,asubclassofthe Phone class.
PhoneNotifier
Thisinterface specifiestheAPIatelephonyimplementationusestonotifyaphonestatelistenerofstatechanges.
PhoneStateIntentReceiver
This classhandles Intent objectsthathaveintenttypesspecifiedinthe TelephonyIntents class.ThisclassenablesAndroidapplicationstousetheIntentssystemtoobtainphonestateinformation.
PhoneSubInfo
Thisclass containsmethodsforobtaininginformationaboutamobileservicesubscriber,suchastheuniqueidentifyingnumberforthehandset(IMEI),theuniqueidentifyingnumberforthesubscriber(IMSI),theserialnumberoftheSIMcard,etc.
SimCard
This interfacedefinestheAPIforaccessingtheSIMcard.
TelephonyIntents
Thisclass definesconstantsforbroadcastintentsthathavesimilarfunctionalitytotheTelephonyManagerAPI.
TelephonyProperties
Thisclass definestheconstantsusedwiththe SystemProperties classforsettingandgettingtelephony-relatedproperties.
TheseclassesarenotdocumentedintheAndroidSDKdocumentation,butthedescriptionshereshouldgiveyousomeunderstandingofthesourcecodefortheseclasses.
15.2.3.Theandroid.internal.telephony.gsmPackage
ManyoftheclassesandinterfacesintheprevioussectionaretypicalofaJavaAPIthatcanhavemultipleimplementations.TheimplementationsoftheAPIdefinedinthe telephony.internal packagecorrespondtoalibraryusedintheRIL.TobetterunderstandthisAPI,wewilllookatoneimplementationherethatsupportsGSM.
Thus,thissectiondelvesfurtherintothetelephonyinternalsofAndroid,lookingespeciallyathowtheinterfacesandabstractbaseclassesareimplementedandsubclassedtoenableaccesstothefunctionalityofGSMtelephony.AlthoughitmayseemthatspecificationssuchasTS27.007covermobiletelephonyingeneral,thislayerofAndroidactuallyhastoaccommodatevariationsinmobiletelephonystandards.InCDMAtelephony,forinstance,theSIMcardisanoptionalpartofthestandardandisrarelypresentinCDMAhandsets.Inthiscase,thepackagedescribedinthissectionwouldbereplacedbyaCDMA-orientedpackagewithasimilararchitecturalrelationshiptothehigher-levelclassesdescribedintheprevioussection.TheRILcodeisalsospecifictothetypeoftelephonyinthehandset.
AttheRILlayer,thedifferencesbetweenGSMandCDMAaremainlyoutsidethecorefunctionalityofmakingphonecalls,soyoumaybewonderingwhyalltheselayersandAPIsarenecessary.But,asthedescriptionoftheclassesspecifictocommunicatingwithaGSMRILwillshow,thereareplentyofdifferencesindetail,suchasSIMcards,thetypeofmobiledatanetwork,etc.Thesemakeitimpracticaltodesignauniversalinterfacetomobileradios,despitetheuseofastandardprotocolforcommunicatingwiththem:
AdnRecord
Thisclassisusedtoloadandstore AbbreviatedDialingNumbers(ADNs)toandfromtheSIMcard.ADNsareshortnumbersusedforinformationcalls,emergencycalls,etc.
AdnRecordCache
Thisclasscaches andenablesaccesstoADNs.
ApnSetting
Thisclass holdsdataspecifyingtheaccesspointname(APN)andotherparametersforconnectingtoGeneralPacketRadioService(GPRS)and3Gmobiledatanetworks.ThismobiledatatechnologyisspecifictoGSMnetworks.
BaseCommands
ThisclassimplementstheCommandsInterfaceinterface,whichisusedthroughoutthe GSM telephonyclassestocommunicatewiththeGSMradio.
CallFailCause
This interfacedefinesconstantsfordecodingfailurecausecodes.
CallForwardInfo
Thisclassholds datathatcorrespondstotheparametersofacall-forwardingcommandtotheRIL.
CallTracker
Thisclass mapsinformationfromtheRILtostatetransitionsforthe GSMCall class.
CommandException
Thisclass isanexceptionthrownwhentheRILreportsanerrorfromacommand.
CommandsInterface
Thisinterface definestheAPItotheGSMRIL.Thisinterfaceisimplementedbythe BaseCommands class.
DataConnectionTracker
Thistracks thestateofGPRSpacketdataprotocol(PDP)connections.ThistypeofconnectionisspecifictoGSMmobiledata.
DataLink
Thisclass implementstheDataLinkInterfaceinterfaceandisusedinthe PPPLink class,whichmanagespointtopointprotocol(PPP)linksinGPRSnetworking.
DataLinkInterface
This class
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