Twilio's Programmable Voice SIP Interface product enables you to use your existing SIP communications infrastructure to initiate SIP sessions with the Twilio ...
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ProgrammableVoice
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GettingStartedwithProgrammableVoice
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BeforeyouBegin
BeforeyoucanuseSIPInterface,youmustsignupforaTwilioaccount(ifyoudon'talreadyhaveone).Tosignupforanaccountclickhere.
Overview
ConnectyourcommunicationsinfrastructuretoTwilioandstartbuildingprogrammablevoiceapplications,suchascallcentersandIVRs,withTwilio’spowerfulandflexiblevoicecapabilities.YoucanconnecttoTwiliooverthepublicinternetoralternativelyviaaprivateconnectionusingTwilio’sInterconnect.ProgrammableVoiceSIPletsyourouteyourvoicecallswithglobalreachtoanylandlinephone,mobilephone,browser,mobileapp,oranyotherSIPendpoint.
ThefollowingdiagramillustratesthepositionoftheTwilioCloudinthecallflows.
WhatisSIP?
SessionInitiationProtocol(SIP)isastandardizedcommunicationsprotocolthathasbeenwidelyadoptedformanagingmultimediacommunicationsessionsforvoiceandvideocalls.SIPmaybeusedtoestablishconnectivitybetweenyourcommunicationsinfrastructuressuchasanon-premiseorvirtualPBXandTwilio'scommunicationsplatform.
SendingSIPtoTwilio
Twilio’sProgrammableVoiceSIPInterfaceproductenablesyoutouseyourexistingSIPcommunicationsinfrastructuretoinitiateSIPsessionswiththeTwilioCloud.SIPInterfaceusesTwilio’sTwiMLlanguageand/orTwilio’sRESTAPIstocreateadvancedvoiceapplications.LearnhowtogetstartedconnectingyourSIPcommunicationsinfrastructuretotheTwilioCloud.
ReceivingSIPfromTwilio
Twilio’sProgrammableVoiceSIPInterfaceproductenablesyouradvancedvoiceapplicationstoinitiateSIPsessionsfromtheTwilioCloudtowardsyourexistingSIPcommunicationsinfrastructureusingTwilio’sTwiMLlanguageand/orTwilio’sRESTAPIs.LearnhowtogetstartedconnectingtheTwilioCloudtoyourSIPcommunicationsinfrastructure.
Limits
MakesureyouareawareofthefollowingProgrammableVoiceSIPDomainlimits.
100SIPDomainsperAccountorSubAccount
IPAccessControlLists(ACLs)limits
CredentialListslimits
SIPRegistrationlimits
Features
SIPRegistration
TwilioallowsyoutoregisteryourSIPPhonesorSIPEndpointswithTwilio.SIPRegistrationisusedtoidentifythelocationoftheSIPEndpoints.Therefore,theusercanreceivecallsirrespectiveofphysicallocationoftheSIPEndpoint.
ThisfeatureallowsyourSIPEndpointscansendREGISTERrequesttoTwilio.Fordetailsseehere.
CallTransfersusingSIPREFERfromTwilio
Calltransferenablesyoutomoveanactivecallfromoneendpointtoanother,inSIPthisisaccomplishedusingtheSIPREFERmethod.
TwiliosupportsinitiatingSIPREFERmethodfromTwiliotowardsyourIPcommunicationsinfrastructureleveragingtheverb.
SIPCustomHeader
SIPcustomheaderallowsyoutosendcustomizedheaders.
UUI(User-to-UserInformation)Header
UUIheaderallowsyoutosendcontextualinformationovertheSIPcall.YoucancheckSending-sipwithUUIandReceiving-sipwithUUIforfurtherUUIdetails.
DTMF
TwiliosupportsRFC-2833forsendingandreceivingDTMF.
Mediacodec
TwiliosupportsG.711μ-law(PCMU)andA-law(PCMA)codecsformedia.Thesearethemostpopularcodecsusedbycarrierssotranscodingisunnecessary.
SecuringSIPTrafficusingTLS
Encryptionensuresthatthecallsignalingremainsprivateduringtransmission.TransportLayerSecurity(TLS)providesencryptionforSIPsignaling.
ToenableTLS,ensurethatyouhaveimportedTwilio'sRootCACertificate.ThereisnofurtherconfigurationrequiredforTLSandyoucanstartsendingoverport5061straightaway.TLSFunctionality/Port5061isalwaysactiveanddoesnotrequireamanualtogglelikeSecureMedia.TostopusingTLS,simplysendSIPtoPort5060orremovethetransport=tlsparameter.
SIPInterfacesupportsthefollowingconfigurationsforTLS:
5060(noTLS,NoSecureMedia)
5061(TLS,NoSecureMedia)
5061(TLS,SecureMedia)
ForcallswhereTLSisactivethiswillcausecertainfunctionalitytobehavedifferently:
SIPPCAPsfromtheconsolewillproduceonlyablankfile.
Callmetadatawillcontinuetobeavailableforexamplemajorerrorcodes,starttime,endtime,to/from.
SIPReferwillfunctionasexpectedusingTLS.
WhensendingTLSSIPtraffictoTwilio,youwillneedtoensurethatyourinfrastructureisusingnext-hopdomainasopposedtonext-hopip.Thisisacommonmisconfigurationandwillcausea403errorthatwillnotbevisibleonyourTwilioaccount.Trafficmustbesenttothedomain{example}.sip.{region}.twilio.com,ratherthananIPaddressinordertoassociatethetrafficwithyourTwilioaccount.
SecureMedia
SecureMediausesencryptiontoensurethatthecallmediaandassociatedsignalingremainsprivateduringtransmission.SecureReal-TimeProtocol(SRTP)providesencryptionformedia.Fordetailsseehere.
TLS/SRTPSpecifications
SIPTLS
Versions:TwiliosupportsTLSv1.0,TLSv1.1andTLSv1.2.
PLEASENOTE:Tobettercomplywithsecurityrequirements,wehavedeprecatedTLSv1.0andTLSv1.1forinboundandoutboundSIPcalls,aswellasSIPregistration.IfyourSIPinfrastructurerequiresusingTLSv1.0orTLSv1.1,youcanconfigureyourTwilioAccounttoallowthesedeprecatedversionsinyourconsoleunderVoice→Settings→AllowDeprecatedSIP/TLSversions.Ifthissettingisenabled,yourSIPendpointscanusethedeprecatedTLSv1.0andTLSv1.1versionsforSIPsignalingsenttoorreceivedfromTwilio.Ifdisabled,onlynon-deprecatedTLSv1.2+isallowed.TwiliostronglyrecommendstheuseofTLSversion1.2whenconnectingyourSIPinfrastructure.
Ciphers:ECDHE-ECDSA-AES128-GCM-SHA256,ECDHE-RSA-AES128-GCM-SHA256,ECDHE-ECDSA-AES128-SHA256,ECDHE-RSA-AES128-SHA256,ECDHE-ECDSA-AES256-GCM-SHA384,ECDHE-RSA-AES256-GCM-SHA384,ECDHE-ECDSA-AES256-SHA384,ECDHE-RSA-AES256-SHA384,AES128-GCM-SHA256,AES128-SHA256,AES128-SHA,AES256-GCM-SHA384,AES256-SHA256,AES256-SHA
IfyouareusingTwiMLtosendSIPfromTwilio,toenableencryptionyoumustusethetransport=tlsparameterinyourSIPnouninyourDialverb.
Bydefaultport5061willbeusedforTLS,however,youmayspecifytheportyouwishtouseinyourURI.
SecureMedia
SendingSRTPtoTwilio:TwiliosupportsthefollowingCryptosuites:AES_CM_128_HMAC_SHA1_80andAES_CM_128_HMAC_SHA1_32.Bothmaybeincludedinyourorderofpreference.
ReceivingSRTPfromTwilio:Onlyasinglecryptosuitewillbeadvertised:AES_CM_128_HMAC_SHA1_80
ImportingTwilio'sRootCACertificateTLSisusedtoencryptSIPsignalingbetweenSIPendpoints.InorderforthistofunctionproperlyitisrequiredthatcertaindevicesinthenetworkimportaCAcertificate.TwiliousescertificatesfromaCA(CertificateAuthority).Itisimportantthatyouaddthefollowingrootcertificatetoyourcommunicationsinfrastructuretoestablishitsauthenticity.DownloadTwilio'sCAcertificate.ItisimportanttonotethatTwiliousesawildcardcertificatewhichcanbeusedformultiplesubdomainsofadomain(*.sip.twilio.com).Ifyournetworkelementdoesnotsupportwildcardedcertificatespleasedisablecertificatevalidation.
TwiliosRootCAcontainsacertificatechainsignedbymultipleCertificateAuthorities.YoushouldimporttheentirePEMfileratherthanindividualcertificates.
Twiliodoesnotsupportimportingrootcertificatesfromathirdpartyatthispointintime.InordertouseTwilioVoicewithTLS,theTwilioRootCAmustbeused.
Note:TwilioSIPInterfaceoutboundcallURIconfigurationsusingthesipsURIschemeinordertoenableend-to-endencryptionisNOTsupportedbyTwilio.However,wedosupportsipURIschemesusingtransport=tlsforpoint-to-pointencryption.
IfyouconfigureyourSIPInterfaceURIstousesipsschemes,thesesipsURIswillbehandledasiftheyweresipURIsusingTLStransport.TwiliowilleffectivelyadjusttheURIinternallytoinsteadberoutedusingthesipschemeandtransport=tlsontheoutboundmessages,resultinginpoint-to-pointencryptionbetweenTwilioandthecustomerequipment.
TwiliostronglysuggestsnotusingsipsschemesinyourTwilioSIPconfigurations,asthiscouldcausepossiblyunintendedbehavior,duetohowweprocesssuchURIs.Instead,wesuggestusingsipschemeswithTLStransport.Thismethod,alongwiththesecurityofourvoicearchitectureandSuperNetwork,isaneffectivewayofaddingencryptiontoyourTwilioSIPconnections.
IPaddresses
PrepareyourcommunicationsinfrastructuretomakesurethatyourSIPinfrastructurehasconnectivitytotheTwilioCloudandviceversa.Toensurethatyourcommunicationsinfrastructuredoesn’tblockcommunication,youmustupdateyourlistofallowedIPaddresses.WestronglyencourageyoutoallowallofthefollowingIPaddressrangesandportsonyourfirewallforSIPsignalingandRTPmediatraffic.
ThisisimportantifyouhaveNumbersindifferentregionsaswellasforavailabilitypurposes(e.g.ifNorthAmericaVirginiagatewaysaredown,thenNorthAmericaOregongatewayswillbeused).
PleaseseeTwilio'sSIPIPaddressesforthecompletelist.
Glossary
CommunicationsInfrastructure
AbroadtermtorefertoIP-PBX,SBC,IP-phones,etc...
SIPEndpoint
IP-phoneorasoftclientwithwhichauserinitiatesaVoIPcall
SIPURI
EquivalenttoaSIPphonenumberandtakestheform,sip:username@SIPDomain
TwilioSIPDomain
Ittakestheform{example}.sip.{region}.twilio.comwhere{example}isspecifiedbythecustomerand{region}isthedatacenterwheretheregistrarislocated.Initiallyonlyus1.
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Wealldosometimes;codeishard.Gethelpnowfromoursupportteam,orleanonthewisdomofthecrowdbyvisitingTwilio'sStackOverflowCollectiveorbrowsingtheTwiliotagonStackOverflow.
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