SS7 & SIP

ableofContents 1.Introduction...................... 1.Introducti on...........................................3 .....................3 2.Scope............................. 2.Scope..... .............................................3 .....................3 3.Scenarios......................... 3.Scenarios. .............................................5 .....................5 4.SIPMechanismsRequired........... 4.SIPMechan ismsRequired................................6 .....................6

Camarillo/Roach/Peterson/Ong Camarillo/Roach/Peters on/Ong[Page1 [Page1] ] ISUPtoSIPMapping ISUPtoSIPMapping August200 August2001 1 4.1."Transparent"TransitofISUPmessages.................6 4.1."Transparent"TransitofISUPmess ages.................6 4.2.UnderstandingofMultipartBodies. 4.2.Understand ingofMultipartBodies......................6 .....................6 4.3.TransmissionofDTMFinformation.. 4.3.Transmissi onofDTMFinformation.......................7 .....................7 4.4.ReliableTransmissionofProvision 4.4.ReliableT ransmissionofProvisionalResponses.........7 alResponses.........7 4.5.ProvisionalMediaStreams......... 4.5.Provisiona lMediaStreams..............................7 .....................7 4.6.Mid-CallTransactionsWhichdonot 4.6.Mid-CallT ransactionsWhichdonotChangeSIPState....7 ChangeSIPState....7 5.Mapping........................... 5.Mapping... .............................................7 .....................7 6.SIPtoISUPmapping............... 6.SIPtoISU Pmapping....................................8 .....................8 6.1.CallFlows........................ 6.1.CallFlows .............................................8 .....................8 6.1.1.En-blocCallSetup(nonauto-answe 6.1.1.En-blocCa llSetup(nonauto-answer)...................8 r)...................8 6.1.2.Auto-answercallsetup............ 6.1.2.Auto-answe rcallsetup.................................10 .....................10 6.1.3.ISUPT7expires................... 6.1.3.ISUPT7ex pires........................................10 .....................10 6.1.4.SIPTimeout....................... 6.1.4.SIPTimeou t............................................11 .....................11 6.1.5.ISUPSetupFailure................ 6.1.5.ISUPSetup Failure.....................................12 .....................12 6.1.6.CausepresentinACMmessage...... 6.1.6.Causepres entinACMmessage...........................13 .....................13 6.1.7.CallcancelledbySIPnode........ 6.1.7.Callcance lledbySIPnode.............................14 .....................14 6.2.StateMachine..................... 6.2.StateMach ine..........................................15 .....................15 6.2.1.INVITEreceived................... 6.2.1.INVITErec eived........................................16 .....................16 6.2.1.1INVITEtoIAMprocedures.......... 6.2.1.1INVITEto IAMprocedures...............................17 .....................17 6.2.2.ISUPT7expires................... 6.2.2.ISUPT7ex pires........................................19 .....................19 6.2.3.CANCELorBYEreceived............ 6.2.3.CANCELor BYEreceived.................................19 .....................19 6.2.4.RELreceived...................... 6.2.4.RELreceiv ed...........................................20 .....................20 6.2.4.1ISDNCauseCodetoSIPStatusCode 6.2.4.1ISDNCause CodetoSIPStatusCodemapping.............20 mapping.............20 6.2.5.EarlyACMreceived................ 6.2.5.EarlyACM received.....................................23 .....................23 6.2.6.ACMreceived...................... 6.2.6.ACMreceiv ed...........................................23 .....................23 6.2.7.CONorANMreceived............... 6.2.7.CONorANM received....................................24 .....................24 6.2.8.TimerT9expires.................. 6.2.8.TimerT9e xpires.......................................24 .....................24 6.2.9.CPGreceived...................... 6.2.9.CPGreceiv ed...........................................24 .....................24 6.2.10.ACKreceived...................... 6.2.10.ACKreceiv ed...........................................25 .....................25 7.ISUPtoSIPmapping............... 7.ISUPtoSI Pmapping....................................25 .....................25 7.1.CallFlows........................ 7.1.CallFlows .............................................25 .....................25 7.1.1.En-bloccallsetup(nonauto-answe 7.1.1.En-blocca llsetup(nonauto-answer)...................25 r)...................25 7.1.2.Auto-answercallsetup............ 7.1.2.Auto-answe rcallsetup.................................27 .....................27 7.1.3.SIPTimeout....................... 7.1.3.SIPTimeou t............................................27 .....................27 7.1.4.ISUPT9Expires................... 7.1.4.ISUPT9Ex pires........................................28 .....................28 7.1.5.SIPErrorResponse................ 7.1.5.SIPError Response.....................................30 .....................30 7.1.6.SIPRedirection................... 7.1.6.SIPRedire ction........................................30 .....................30 7.1.7.CallCancelledbyISUP............ 7.1.7.CallCance lledbyISUP.................................32 .....................32 7.2.StateMachine..................... 7.2.StateMach ine..........................................33 .....................33 7.2.1.InitialAddressMessagereceived.. 7.2.1.InitialAd dressMessagereceived.......................34 .....................34 7.2.1.1IAMtoINVITEprocedures.......... 7.2.1.1IAMtoINV ITEprocedures...............................34 .....................34 7.2.2.100received...................... 7.2.2.100receiv ed...........................................36 .....................36 7.2.3.18xreceived...................... 7.2.3.18xreceiv ed...........................................36 .....................36 7.2.4.200received...................... 7.2.4.200receiv ed...........................................37 .....................37 7.2.5.3xxreceived...................... 7.2.5.3xxreceiv ed...........................................38 .....................38 7.2.6.4xx-6xxreceived................ 7.2.6.4xx-6xx received.....................................38 .....................38

7.2.6.1SIPStatusCodetoISDNCauseCodemapping.............38 7.2.6.1SIPStatusCodetoISDNCauseCode mapping.............38 7.2.7.RELreceived...................... 7.2.7.RELreceiv ed...........................................40 .....................40

Camarillo/Roach/Peterson/Ong Camarillo/Roach/Peters on/Ong[Page2 [Page2] ] ISUPtoSIPMapping ISUPtoSIPMapping August200 August2001 1 7.2.8.ISUPT11Expires.......................................40 7.2.8.ISUPT11Expires.................. .....................40 8.Suspend/Resumeandhold........... 8.Suspend/Re sumeandhold................................41 .....................41 8.1.SUSandRES....................... 8.1.SUSandRE S............................................41 .....................41 8.2.Hold(re-INVITE).................. 8.2.Hold(re-I NVITE).......................................41 .....................41 9.NormalReleaseoftheConnection.. 9.NormalRel easeoftheConnection.......................42 .....................42 9.1.SIPinitiated..................... 9.1.SIPinitia ted..........................................42 .....................42 9.2.ISUPInitiated.................... 9.2.ISUPIniti ated.........................................43 .....................43 9.2.1.Callerhangsup................... 9.2.1.Callerhan gsup........................................43 .....................43 9.2.2.Calleehangsup................... 9.2.2.Calleehan gsup........................................43 .....................43 10.ISUPmaintenancemessages......... 10.ISUPmaint enancemessages..............................43 .....................43 10.1.Resetmessages.................... 10.1.Resetmess ages.........................................44 .....................44 10.2.Blockingmessages................. 10.2.Blockingm essages......................................44 .....................44 10.3.Continuitychecks................. 10.3.Continuity checks......................................44 .....................44 11.ConstructionofTelephonyURIs.... 11.Constructi onofTelephonyURIs.........................45 .....................45 12.OtherISUPflavors................ 12.OtherISUP flavors.....................................48 .....................48 12.1.GuidelinestosendotherISUPmess 12.1.Guidelines tosendotherISUPmessages.................49 ages.................49 13.Acronyms.......................... 13.Acronyms.. .............................................50 .....................50 14.Acknowledgments................... 14.Acknowledg ments........................................51 .....................51 15.RevisionHistory.................. 15.RevisionH istory.......................................51 .....................51 16.References........................ 16.References .............................................51 .....................51 17.SecurityConsiderations........... 17.SecurityC onsiderations................................53 .....................53 18.Authors'Addresses................ 18.Authors'A ddresses.....................................53 .....................53 1.Introduction SIP[1]isanapplicationlayerprotocolforestablishing, terminatingandmodifyingmultimediasessio terminatingandmod ifyingmultimediasessions.Itistypically ns.Itistypically carriedoverIP.Telephonecallsareconsid carriedoverIP.Te lephonecallsareconsideredatypeofmultimedia eredatypeofmultimedia sessionswherejustaudioisexchanged. ISUP[2]isalevel4protocolusedinSS7networks.Ittypically ISUP[2]isalevel4protocolusedinSS7 networks.Ittypically runsoverMTPalthoughitcanalsorunover runsoverMTPaltho ughitcanalsorunoverIP[15].ISUPisusedfo IP[15].ISUPisusedfor r controllingtelephonecallsandformainten controllingtelepho necallsandformaintenanceofthenetwork anceofthenetwork (blockingcircuits,resettingcircuitsetc.). Amoduleperformingthemappingbetweenthesetwoprotocolsis Amoduleperformingthemappingbetweenthe setwoprotocolsis usuallyreferredtoasMediaGatewayContro usuallyreferredto asMediaGatewayController(MGC),althoughthe ller(MGC),althoughthe terms'softswitch'or'callagent'arealso terms'softswitch' or'callagent'arealsosometimesused.AnMGC sometimesused.AnMGC haslogicalinterfacesfacingbothnetworks haslogicalinterfa cesfacingbothnetworks,thenetworkcarrying ,thenetworkcarrying ISUPandthenetworkcarryingSIP.TheMGC ISUPandthenetwor kcarryingSIP.TheMGCalsohassomecapabilitie alsohassomecapabilities s forcontrollingthevoicepath;thereisty forcontrollingthe voicepath;thereistypicallyaMediaGateway picallyaMediaGateway (MG)withE1/T1trunkinginterfaces(voice (MG)withE1/T1tru nkinginterfaces(voicefromPSTN)andwithIP fromPSTN)andwithIP interfaces(VoIP).TheMGCandtheMGcanb interfaces(VoIP). TheMGCandtheMGcanbemergedtogetherinone emergedtogetherinone physicalboxorkeptseparate. TheseMGCsarefrequentlyusedtobridgeSIPandISUPnetworksso TheseMGCsarefrequentlyusedtobridgeSI PandISUPnetworksso thatcallsoriginatinginthePSTNcanreac thatcallsoriginat inginthePSTNcanreachIPtelephoneendpoints hIPtelephoneendpoints

Camarillo/Roach/Peterson/Ong Camarillo/Roach/Peters on/Ong[Page3 [Page3] ] ISUPtoSIPMapping ISUPtoSIPMapping August200 August2001 1 andviceversa.ThisisusefulforcasesinwhichPSTNcallsneedto andviceversa.Thisisusefulforcasesin whichPSTNcallsneedto takeadvantageofservicesinIPworld,in takeadvantageofs ervicesinIPworld,inwhichIPnetworksareuse whichIPnetworksareused d astransitnetworksforPSTN-PSTNcalls,ar astransitnetworks forPSTN-PSTNcalls,architecturesinwhichcall chitecturesinwhichcalls s originateondesktop'softphones'buttermi originateondeskto p'softphones'butterminateatPSTNterminals, nateatPSTNterminals, andmanyothersimilarnext-generationtele andmanyothersimi larnext-generationtelephonearchitectures. phonearchitectures. ThisdocumentdescribeslogicandprocedureswhichanMGCmightuse Thisdocumentdescribeslogicandprocedure swhichanMGCmightuse toimplementthemappingbetweenSIPandIS toimplementthema ppingbetweenSIPandISUPbyillustratingthe UPbyillustratingthe correspondences,atthemessagelevelandp correspondences,at themessagelevelandparameterlevel,between arameterlevel,between theprotcols.Italsodescribestheinterp theprotcols.Ita lsodescribestheinterplaybetweenparallelstat laybetweenparallelstate e machinesforthesetwoprotocolsasarecom machinesforthese twoprotocolsasarecommendationforimplementor mendationforimplementors s tosynchronizeprotocoleventsininterwork tosynchronizeprot ocoleventsininterworkingarchitectures. ingarchitectures. 2.Scope ThisdocumentfocusesonthetranslationofISUPmessagesintoSIP Thisdocumentfocusesonthetranslationof ISUPmessagesintoSIP messages,andthemappingofISUPparameter messages,andthem appingofISUPparametersintoSIPheaders.The sintoSIPheaders.The purposeoftranslationinISUP-SIPinterwor purposeoftranslat ioninISUP-SIPinterworkingistwofold:forISUP kingistwofold:forISUP callsthattraverseaSIPnetwork,translat callsthattraverse aSIPnetwork,translationallowsSIPelements ionallowsSIPelements suchasproxyserverstomakeroutingdecis suchasproxyserve rstomakeroutingdecisionsbasedonISUP ionsbasedonISUP criteriasuchasthecalledpartynumber;t criteriasuchasth ecalledpartynumber;translationalsoprovides ranslationalsoprovides criticalinformationaboutthecalltoSIP criticalinformatio naboutthecalltoSIPendpointsthatcannot endpointsthatcannot understandencapsulatedISUP(orperhapswh understandencapsul atedISUP(orperhapswhichmerelycannot ichmerelycannot understandtheparticularISUPvariantinuse). ThisdocumentonlytakesintoaccountthecallfunctionalityofISUP Thisdocumentonlytakesintoaccountthec allfunctionalityofISUP. . MaintenancemessagesdealingwithPSTNtrun Maintenancemessage sdealingwithPSTNtrunksaretreatedonlyasfa ksaretreatedonlyasfar r astheyaffectthecontrolofanongoingca astheyaffectthe controlofanongoingcall;otherwisethese ll;otherwisethese messageneitherhavenorrequireanyanaloginSIP. MessagesindicatingerrororcongestionsituationsinthePSTN Messagesindicatingerrororcongestionsit uationsinthePSTN (MTP-3)andtherecoverymechanismsusedsu (MTP-3)andtherec overymechanismsusedsuchasUserPartAvailable chasUserPartAvailable andUserPartTestISUPmessagesareoutsid andUserPartTest ISUPmessagesareoutsidethescopeofthis ethescopeofthis document ThereareseveralflavorsofISUP.ITU-TQ.767InternationalISUP[2 ThereareseveralflavorsofISUP.ITU-TQ. 767InternationalISUP[2] ] isusedthroughthisdocument;somediffere isusedthroughthi sdocument;somedifferenceswithANSIISUP[3] nceswithANSIISUP[3] andTTCISUPareoutlined.ISUPQ.767[2]i andTTCISUPareou tlined.ISUPQ.767[2]isusedinthisdocument susedinthisdocument becauseitistheleastcomplexofallthe becauseitisthel eastcomplexofalltheISUPflavors.Duetothe ISUPflavors.Duetothe smallnumberoffieldsthatmapdirectlyfr smallnumberoffie ldsthatmapdirectlyfromISUPtoSIP,the omISUPtoSIP,the signalingdifferencesbetweenQ.767andspe signalingdifferenc esbetweenQ.767andspecificnationalvariantso cificnationalvariantsof f ISUPwillgenerallyhavelittletonoimpac ISUPwillgenerally havelittletonoimpactonthemapping.Note, tonthemapping.Note, however,thattheITU-Thasnotsubstantial however,thattheI TU-Thasnotsubstantiallystandarizedpractices lystandarizedpractices forLocalNumberPortabilitysinceportabil forLocalNumberPo rtabilitysinceportabilitytendstobegrounded itytendstobegrounded innationalnumberingplanpractices,andt innationalnumberi ngplanpractices,andthatconsequentlyLNPmust hatconsequentlyLNPmust bedescribedonavirtuallyper-nationbasis. MappingofSIPheaderstoISUPparametersi MappingofSIPhead erstoISUPparametersinthisdocumentfocuses nthisdocumentfocuses

Camarillo/Roach/Peterson/Ong Camarillo/Roach/Peters on/Ong[Page4 [Page4] ] ISUPtoSIPMapping ISUPtoSIPMapping August200 August2001 1 largelyonthemappingbetweentheparametersfoundintheISUP largelyonthemappingbetweentheparamete rsfoundintheISUP InitialAddressMessage(IAM)andtheheade InitialAddressMes sage(IAM)andtheheadersassociatedwiththeSI rsassociatedwiththeSIP P INVITEmessage;bothofthesemessagesare INVITEmessage;bot hofthesemessagesareusedintheirrespective usedintheirrespective protocolstorequesttheestablishmentofa protocolstoreques ttheestablishmentofacall.OnceanINVITEhas call.OnceanINVITEhas beensentforaparticularsession,suchhe beensentforapar ticularsession,suchheadersastheToandFrom adersastheToandFrom fieldbecomeessentiallyfixed,andnofurt fieldbecomeessent iallyfixed,andnofurthertranslationwillbe hertranslationwillbe requiredduringsubsequentsignaling,which requiredduringsub sequentsignaling,whichisroutedinaccordance isroutedinaccordance withViaandRouteheaders.Hence,theprob withViaandRoute headers.Hence,theproblemofparameter-to-heade lemofparameter-to-header r mappinginSIP-Tisconfinedmoreorlesst mappinginSIP-Tis confinedmoreorlesstotheIAMandtheINVITE. otheIAMandtheINVITE. Someadditionaldetailisgiveninthepopu Someadditionaldet ailisgiveninthepopulationofparametersin lationofparametersin theISUPACMandRELmessagesbasedonSIPstatuscodes. ThisdocumentdescribeswhenthemediapathassociatedwithaSIP Thisdocumentdescribeswhenthemediapath associatedwithaSIP callistobeinitialized,terminated,modi callistobeiniti alized,terminated,modified,etc.,butitdoes fied,etc.,butitdoes notgointodetailssuchashowtheinitial notgointodetails suchashowtheinitializationisperformedor izationisperformedor whichprotocolsareusedforthatpurpose. 3.Scenarios ThereareseveralscenarioswhereISUP-SIPmappingtakesplace.The ThereareseveralscenarioswhereISUP-SIP mappingtakesplace.The waythemessagesaregeneratedisdifferent waythemessagesar egeneratedisdifferentdependingonthe dependingonthe scenario. WhenthereisasingleMGCandthecallisfromaSIPphonetoaPST WhenthereisasingleMGCandthecallis fromaSIPphonetoaPSTN N phone,orviceversa,theMGCgeneratesthe phone,orvicevers a,theMGCgeneratestheISUPmessagesbasedon ISUPmessagesbasedon themethodsdescribedinthisdocument. +-------------++-----++-------------+ |PSTNswitch+-------+MGC+-------+SIPUAC/UAS| +-------------++-----++-------------+ ThescenariowhereacalloriginatesinthePSTN,goesintoaSIP Thescenariowhereacalloriginatesinthe PSTN,goesintoaSIP networkandterminatesinthePSTNagainis networkandtermina tesinthePSTNagainisknownas"SIPbridging". knownas"SIPbridging". SIPbridgingshouldprovideISUPtransparen SIPbridgingshould provideISUPtransparencybetweenthePSTN cybetweenthePSTN switcheshandlingthecall.Thisisachieve switcheshandlingt hecall.Thisisachievedbyencapsulatingthe dbyencapsulatingthe incomingISUPmessagesinthebodyoftheS incomingISUPmessa gesinthebodyoftheSIPmessages(see[4]).I IPmessages(see[4]).In n thiscase,theISUPmessagesgeneratedbyt thiscase,theISUP messagesgeneratedbytheegressMGCaretheone heegressMGCaretheones s presentintheSIPbody(possiblywithsome presentintheSIP body(possiblywithsomemodifications;for modifications;for example,ifthecallednumberinthereques example,ifthecal lednumberintherequestURIisdifferentfrom tURIisdifferentfrom theonepresentintheISUPduetoSIPredi theonepresentin theISUPduetoSIPredirection,theISUPmessage rection,theISUPmessage willneedtobeadjusted). +------++-------------++-----++------------++------+ +------++-------------++-----++-----------++------+ |PSTN+---+IngressMGC+---+SIP+---+Eg |PSTN+---+Ingres sMGC+---+SIP+---+EgressMGC+---+PSTN| ressMGC+---+PSTN| +------++-------------++-----++--+------++------------++-----++------------++------+ ---------++------+ SIPisusedinthemiddleofbothMGCsbecausethevoicepathhasto SIPisusedinthemiddleofbothMGCsbeca usethevoicepathhasto beestablishedthroughtheIPnetworkbetwe beestablishedthro ughtheIPnetworkbetweenbothMGs;this enbothMGs;this

Camarillo/Roach/Peterson/Ong Camarillo/Roach/Peters on/Ong[Page5 [Page5] ]

ISUPtoSIPMapping ISUPtoSIPMapping August200 August2001 1 structurealsoallowsthecalltotakeadvantageofcertainSIP structurealsoallowsthecalltotakeadva ntageofcertainSIP services.ISUPmessagesintheSIPbodiesp services.ISUPmess agesintheSIPbodiesprovidefurtherinformatio rovidefurtherinformation n (suchascausevaluesandoptionalparamete (suchascausevalu esandoptionalparameters)tothepeerMGC. rs)tothepeerMGC. Inbothscenarios,theingressMGCplacestheincomingISUPmessages Inbothscenarios,theingressMGCplacest heincomingISUPmessages intheSIPbodybydefault.Notethatthis intheSIPbodyby default.Notethatthishassecurityimplications hassecurityimplications; ; seesection17.Iftherecipientofthesem seesection17.If therecipientofthesemessages(typicallyaSIP essages(typicallyaSIP UAC/UAS)doesnotunderstandthemanegotia UAC/UAS)doesnotu nderstandthemanegotiationusingtheSIP tionusingtheSIP `Accept'and`Require'headerswilltakepl `Accept'and`Requi re'headerswilltakeplaceandtheywillnotbe aceandtheywillnotbe includedinthenextSIPmessageexchange. TherecanbeaSignalingGateway(SG)betweenthePSTNandtheMGC. TherecanbeaSignalingGateway(SG)betwe enthePSTNandtheMGC. ItencapsulatestheISUPmessagesoverIPi Itencapsulatesthe ISUPmessagesoverIPinamannersuchastheon namannersuchastheone e describedin[15].Themappingdescribedin describedin[15]. Themappingdescribedinthisdocumentisnot thisdocumentisnot affectedbytheunderlyingtransportprotocolofISUP. Notethatoverlapdialingmechanisms(useoftheSubsequentAddress Notethatoverlapdialingmechanisms(useo ftheSubsequentAddress Message,SAM)areoutsidethescopeofthis Message,SAM)areo utsidethescopeofthisdocument.Thisdocument document.Thisdocument assumesthatgatewaysfacingISUPnetworks assumesthatgatewa ysfacingISUPnetworksinwhichoverlapdialing inwhichoverlapdialing isusedwillimplementtimerstoinsuretha isusedwillimplem enttimerstoinsurethatalldigitshavebeen talldigitshavebeen collectedbeforeanINVITEistransmittedtoaSIPnetwork. Insomeinstances,gatewaysmayreceiveincompleteISUPmessages Insomeinstances,gatewaysmayreceiveinc ompleteISUPmessages whichindicatemessagesegmentationdueto whichindicatemess agesegmentationduetoexcessivemessagelength. excessivemessagelength. Commonlythesemessageswillbefollowedby Commonlythesemess ageswillbefollowedbyaSegmentationMessage aSegmentationMessage (SGM)containingtheremainderoftheorigi (SGM)containingth eremainderoftheoriginalISUPmessage.An nalISUPmessage.An incompletemessagemaynotcontainsufficie incompletemessage maynotcontainsufficientparameterstoallowfo ntparameterstoallowfor r apropermappingtoSIP;similarly,encapsu apropermappingto SIP;similarly,encapsulating(seebelow)an lating(seebelow)an incompleteISUPmessagemaybeconfusingto incompleteISUPmes sagemaybeconfusingtoterminatinggateways. terminatinggateways. Consequently,agatewaymustwaituntilac Consequently,agat ewaymustwaituntilacompleteISUPmessageis ompleteISUPmessageis received(whichmayinvolvewaitinguntilo received(whichmay involvewaitinguntiloneormoreSGMsarrive) neormoreSGMsarrive) beforesendinganycorrespondingINVITE. 4.SIPmechanismsRequired ForacorrectmappingbetweenISUPandSIP,someSIPmechanismsabov ForacorrectmappingbetweenISUPandSIP, someSIPmechanismsabove e andbeyondthoseavailableinthebaseSIP andbeyondthoseav ailableinthebaseSIPspecificationareneeded. specificationareneeded. Thesemechanismsarediscussedbelow.Ifth Thesemechanismsar ediscussedbelow.IftheSIPUAC/UASinvolvedin eSIPUAC/UASinvolvedin thecalldoesnotsupportthem,itisstill thecalldoesnots upportthem,itisstillpossibletoproceed,but possibletoproceed,but thebehaviorintheestablishmentoftheca thebehaviorinthe establishmentofthecallmaybeslightly llmaybeslightly differentthanthatexpectedbytheuser(e differentthanthat expectedbytheuser(e.g.otherpartyanswers .g.otherpartyanswers beforereceivingtheringbacktone,useris beforereceivingth eringbacktone,userisnotinformedaboutthe notinformedaboutthe callbeingforwarded,etc.). 4.1."Transparent"TransitofISUPmessages Toprovideuserstheabilitytotakeadvantageofthefullrangeof Toprovideuserstheabilitytotakeadvant ageofthefullrangeof servicesaffordedbytheexistingtelephone servicesaffordedb ytheexistingtelephonenetworkwhenplacing networkwhenplacing

Camarillo/Roach/Peterson/Ong Camarillo/Roach/Peters on/Ong[Page6 [Page6] ]

ISUPtoSIPMappingAugust2001 callsfromPSTNtoPSTNacrossaSIPnetwork,SIPmessageswillneed tocarryISUPpayloadsfromgatewaytogateway.Theformatfor carryingthesemessagesisdefinedin"MIMEmediatypesforISUPand QSIGObjects"[4]. SIPclientsandserverswhichdonotunderstandISUParepermittedto ignorethese(andother)optionalMIMEbodies. 4.2.UnderstandingofMultipartBodies InmostPSTNinterworkingsituations,theSIPbodywillberequired tocarrysessioninformation(SDP)inadditiontoISUPand/orbilling information. PSTNinterworkingnodesshouldunderstandtheMIMEtypeof "multipart/mixed"asdefinedinRFC2046[5].Clientsexpresssupport forthisbyincluding"multipart/mixed"inan"Accept"header. 4.3.TransmissionofDTMFinformation Sincethecodecselectedforvoicetransmissionmaynotbeideally suitedforcarryingDTMFinformation,asymbolicmethodof transmittingthisinformationin-bandisdesirable(sinceout-of-band transmissionalonewouldprovidemanychallengesforsynchronization ofthemediastreamfortonere-insertion).Thistransmissionshould beperformedasdescribedin"RTPPayloadforDTMFDigits,Telephony TonesandTelephonySignals"[6],andisinallrespectsorthogonal tothemappingofISUPandSIP. 4.4.ReliableTransmissionofProvisionalResponses Provisionalresponsesareusedinthetransmissionofvariouscall progressinformation.PSTNinterworkinginparticularreliesonthese messagesforcontrolofthemediachannelandtimingofmessages. PSTNinteroperationnodesshouldimplementtheextensiondefinedin "ReliabilityofProvisionalResponsesinSIP"[8]. 4.5.ProvisionalMediaStreams Toallowthetransmissionofmessagesandtonesbeforeafinal connectionhasbeenestablished,SIPnodeswhichinterworkwiththe PSTNneedtobeabletoestablishtemporarymediaconnectionsduring thisperiod. PSTNinteroperatingnodesshouldsupporttheestablishmentof temporaryprovisionalmediastreamsusingthe183statuscode (describedin[9]).

Camarillo/Roach/Peterson/Ong[Page7]

ISUPtoSIPMappingAugust2001 4.6.Mid-CallTransactionsWhichdonotChangeSIPState WheninterworkingwithPSTN,therearesituationswhenPSTNnodes willneedtosendmessageswhichdonotcorrespondtoanySIP operationstoeachotheracrossaSIPnetwork. ThemethodforperformingthistransitwillbeintheINFOmethod, definedin"TheSIPINFOMethod"[10]. NodeswhichdoserveasPSTNinterworkingpointsshouldaccept"405 MethodNotAllowed"and"501NotImplemented"responsestoINFO requestsasnon-fatal. 5.Mapping ThemappingbetweenISUPandSIPisdescribedusingcallflow diagramsandstatemachines.OnestatemachinehandlescallsfromSIP toISUPandthesecondfromISUPtoSIP.Therearedetails,suchas someretransmissionsandsomestates(waitingforRLC,waitingfor ACKetc.),thatarenotshowninthefiguresinordertomakethem easiertofollow. Theboxesrepresentthedifferentstatesofthegateway,andthe arrowsshowchangesinthestate.Theeventthattriggersthechange inthestateandtheactionstotakeappearonthearrow:event/ sectiondescribingtheactionstotake. Forexample,`INVITE/6.2.1'indicatesthatanINVITErequesthas beenreceivedbythegateway,andtheprocedureuponreceptionis describedinthesection6.2.1ofthisdocument. 6.SIPtoISUPmapping 6.1.CallFlows Thefollowingcallflowsillustratetheorderofmessagesintypical successanderrorcaseswhensettingupacallinitiatedfromtheSIP network."100Trying"acknowledgementstoINVITErequestsarenot displayed,sincetheirpresenceisoptional. Inthesediagrams,allcallsignaling(SIP,ISUP)isgoingtoand fromtheMGC;mediahandling(e.g.audiocut-through,trunkfreeing) isbeingperformedbytheMG,underthecontroloftheMGC.Forthe purposeofsimplicity,theseareshownasasinglenode,labeled "MGC/MG."

Camarillo/Roach/Peterson/Ong[Page8] ISUPtoSIPMappingAugust2001 6.1.1.En-blocCallSetup(nonauto-answer) SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<=========Audio===========| ||<-----------ACM-----------|3 4|<----------18x------------|| |<=========Audio===========|| 5|----------PRACK---------->|| 6|<----------200------------|| ||<-----------CPG-----------|7 8|<----------18x------------|| 9|----------PRACK---------->|| 10|<----------200------------|| ||<-----------ANM-----------|11 ||<=========Audio==========>| 12|<----------200------------|| |<=========Audio==========>|| 13|-----------ACK----------->|| (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest. (2)UponreceiptofanINVITErequest,thegatewaymapsittoan IAMmessageandsendsittotheISUPnetwork. (3)TheremoteISUPnodeindicatesthattheaddressissufficient tosetupacallbysendingbackanACMmessage. (4)The"calledpartystatus"codeintheACMmessageismapped toaSIPprovisionalresponse(asdescribedin6.2.5and6.2.6). andreturnedtotheSIPnode.This responsemaycontainSDPtoestablishanearlymediastream (asshowninthediagram).IfnoSDPispresent,theaudio willbeestablishedinbothdirectionsafterstep12. (5)TheSIPnodesendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (6)ThePRACKisconfirmed. (7)IftheISUPvariantpermits, theremoteISUPnodemayissueavarietyofCPGmessagesto indicate,forexample,thatthecallisbeingforwarded.

Camarillo/Roach/Peterson/Ong[Page9]

ISUPtoSIPMappingAugust2001 (8)UponreceiptofaCPGmessage,thegatewaywillmaptheevent codetoaSIPprovisionalresponse(seesection6.2.9.)and sendittotheSIPnode. (9)TheSIPnodesendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (10)ThePRACKisconfirmed (11)OncethePSTNuseranswers,anANMmessagewillbesentto thegateway. (12)UponreceiptoftheANM,thegatewaywillsenda200message totheSIPnode. (13)TheSIPnode,uponreceivinganINVITEfinalresponse(200), willsendanACKtoacknowledgereceipt. 6.1.2.Auto-answercallsetup SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<=========Audio===========| ||<-----------CON-----------|3 ||<=========Audio==========>| 4|<----------200------------|| |<=========Audio==========>|| 5|-----------ACK----------->|| NotethatthisflowisnotsupportedinANSInetworks. (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest. (2)UponreceiptofanINVITErequest,thegatewaymapsittoan IAMmessageandsendsittotheISUPnetwork. (3)Sincetheremotenodeisconfiguredforautomaticanswering, itwillsendaCONmessageuponreceiptoftheIAM.(For ANSI,thismessagewillbeanANM). (4)UponreceiptoftheCON,thegatewaywillsenda200message totheSIPnode. (5)TheSIPnode,uponreceivinganINVITEfinalresponse(200), willsendanACKtoacknowledgereceipt.

Camarillo/Roach/Peterson/Ong[Page10] ISUPtoSIPMappingAugust2001

6.1.3.ISUPT7expires SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<=========Audio===========| ||***T7Expires***| |**MGReleasesPSTNTrunk**| 4|<----------504------------|------------REL---------->|3 5|-----------ACK----------->|| (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest. (2)UponreceiptofanINVITErequest,thegatewaymapsittoan IAMmessageandsendsittotheISUPnetwork.TheISUPtimer T7isstartedatthispoint. (3)TheISUPtimerT7expiresbeforereceiptofanACMorCON message,soaRELmessageissenttocancelthecall. (4)AgatewaytimeoutmessageissentbacktotheSIPnode. (5)TheSIPnode,uponreceivinganINVITEfinalresponse(504), willsendanACKtoacknowledgereceipt. 6.1.4.SIPTimeout SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<=========Audio===========| ||<-----------CON-----------|3 ||<=========Audio==========>| 4|<----------200------------|| |***T1Expires***|| |<----------200------------|| |***T1Expires***|| |<----------200------------|| |***T1Expires***|| |<----------200------------|| |***T1Expires***|| |<----------200------------|| |***T1Expires***|| |<----------200------------|| |***T1Expires***||

Camarillo/Roach/Peterson/Ong[Page11] ISUPtoSIPMappingAugust2001

5|<----------200------------|| |***T1Expires***|| |**MGReleasesPSTNTrunk**| 7|<----------BYE------------|------------REL---------->|6 ||<-----------RLC-----------|8 (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest. (2)UponreceiptofanINVITErequest,thegatewaymapsittoan IAMmessageandsendsittotheISUPnetwork. (3)Sincetheremotenodeisconfiguredforautomaticanswering, itwillsendaCONmessageuponreceiptoftheIAM.InANSIflows, ratherthanaCONanANM(withoutACM)wouldbesent. (4)UponreceiptoftheANM,thegatewaywillsenda200message totheSIPnodeandsetSIPtimerT1. (5)TheresponseisretransmittedeverytimetheSIPtimerT1 expires. (6)Aftersevenretransmissions,thecallistorndownbysending aRELtotheISUPnode,withacausecodeof102(recoveron timerexpiry). (7)ABYEistransmittedtotheSIPnodeinanattempttoclose thecall.Furtherhandlingforthiscleanupisnotshown, sincetheSIPnode'sstateisnoteasilyknowninthis scenario. (8)UponreceiptoftheRELmessage,theremoteISUPnodewill replywithanRLCmessage. 6.1.5.ISUPSetupFailure SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<-----------REL-----------|3 ||------------RLC---------->|4 5|<----------4xx+-----------|| 6|-----------ACK----------->|| (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest.

Camarillo/Roach/Peterson/Ong[Page12] ISUPtoSIPMappingAugust2001 (2)UponreceiptofanINVITErequest,thegatewaymapsittoan

IAMmessageandsendsittotheISUPnetwork. (3)SincetheremoteISUPnodeisunabletocompletethecall,it willsendaREL. (4)Thegatewayreleasesthecircuitandconfirmsthatitis availableforreusebysendinganRLC. (5)ThegatewaytranslatesthecausecodeintheRELtoaSIP errorresponse(seesection6.2.4.)andsendsittotheSIP node. (6)TheSIPnodesendsanACKtoacknowledgereceiptofthe INVITEfinalresponse. 6.1.6.CausepresentinACMmessage SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<=========Audio===========| ||<---ACMwithcausecode---|3 4|<------183withSDP-------|| |<=========Audio===========|| 5|----------PRACK---------->|| 6|<----------200------------|| **Interworktimerexpires** 7|<----------4xx+-----------|| ||------------REL---------->|8 ||<-----------RLC-----------|9 10|-----------ACK----------->|| (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest. (2)UponreceiptofanINVITErequest,thegatewaymapsittoan IAMmessageandsendsittotheISUPnetwork. (3)SincetheISUPnodeisunabletocompletethecallandwants togeneratetheerrortone/announcementitself,itsendsan ACMwithacausecode.Thegatewaystartsaninterworktimer. (4)UponreceiptofanACMwithcause(presenceoftheCAI parameter), thegatewaywillgenerate a183messagetowardstheSIPnode;thiscontainsSDPto

Camarillo/Roach/Peterson/Ong[Page13] ISUPtoSIPMappingAugust2001 establishearlymediacut-through. (5)TheSIPnodesendsaPRACKmessagetoconfirmreceiptofthe

provisionalresponse. (6)ThePRACKisconfirmed. (7)AfinalINVITEresponse,basedonthecausecodereceivedin theearlierACMmessage,isgeneratedandsenttotheSIP nodetoterminatethecall.Seesection6.2.4.forthetable whichcontainsthemappingfromcausecodetoSIPresponse. (8)Uponexpirationoftheinterworktimer,aRELissenttowards thePSTNnodetoterminatethecall.NotethattheSIPnode canalsoterminatethecallbysendingaCANCELbeforethe interworktimerexpires.Inthiscase,thesignaling progressesasinsection6.1.7. (9)UponreceiptoftheRELmessage,theremoteISUPnodewill replywithanRLCmessage. (10)TheSIPnodesendsanACKtoacknowledgereceiptofthe INVITEfinalresponse. 6.1.7.CallcancelledbySIPnode SIPMGC/MGPSTN 1|---------INVITE---------->|| |<----------100------------|| ||------------IAM---------->|2 ||<=========Audio===========| ||<-----------ACM-----------|3 4|<----------18x------------|| |<=========Audio===========|| 5|----------PRACK---------->|| 6|<----------200------------|| |**MGReleasesIPResources**| 7|----------CANCEL--------->|| 8|<----------200------------|| |**MGReleasesPSTNTrunk**| ||------------REL---------->|9 10|<----------487------------|| ||<-----------RLC-----------|11 12|-----------ACK----------->|| (1)WhenaSIPuserwishestobeginasessionwithaPSTNuser, theSIPnodeissuesanINVITErequest.

Camarillo/Roach/Peterson/Ong[Page14] ISUPtoSIPMappingAugust2001 (2)UponreceiptofanINVITErequest,thegatewaymapsittoan IAMmessageandsendsittotheISUPnetwork. (3)TheremoteISUPnodeindicatesthattheaddressissufficient tosetupacallbysendingbackanACMmessage.

(4)The"calledpartystatus"codeintheACMmessageismapped toaSIPprovisionalresponse(asdescribedin6.2.5and6.2.6) andreturnedtotheSIPnode.This responsemaycontainSDPtoestablishanearlymediastream. (5)TheSIPnodesendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (6)ThePRACKisconfirmed. (7)Tocancelthecallbeforeitisanswered,theSIPnodesends aCANCELrequest. (8)TheCANCELrequestisconfirmedwitha200response. (9)UponreceiptoftheCANCELrequest,thegatewaysendsaREL messagetoterminatetheISUPcall. (10)Thegatewaysendsa"487CallCancelled"messagetotheSIP nodetocompletetheINVITEtransaction. (11)UponreceiptoftheRELmessage,theremoteISUPnodewill replywithanRLCmessage. (12)Uponreceiptofthe487,theSIPnodewillconfirmreception withanACK. 6.2.StateMachine NotethatRELcanbereceivedinanystate;thehandlingisthesame foreachcase(seesection6.2.4.).

Camarillo/Roach/Peterson/Ong[Page15] ISUPtoSIPMappingAugust2001 +---------+ +----------------------->|Idle|<---------------------+ |+----+----+| ||| ||INVITE/6.2.1| |V| |T7/6.2.2+-------------------------+REL/6.2.4|

+<----------------+Trying+------------>+ |+-+--------+------+-------+| |CANCEL/6.2.3||||| +<----------------+|E.ACM/|ACM/|CON/| ||6.2.5|6.2.6|6.2.7| |V||| |T9/6.2.8+--------------+||| +<----------+Notalerting|||| |+-------+------+||| |CANCEL/6.2.3||||| |<--------------+|CPG/||| ||6.2.9||| |VV|| |T9/6.2.8+---------------+|REL/6.2.4| +<----------------+Alerting|-|-------------------->| |<----------------+--+-----+------+|| |CANCEL/6.2.3|^||| |CPG/|||ANM/|| |6.2.9+--+|6.2.7|| |VV| |+-------------------------+REL/9.2| ||WaitingforACK|------------>| |+-------------+-----------+| ||| ||ACK/6.2.10| |V| |BYE/9.1+-------------------------+REL/9.2| +<----------------+Connected+------------>+ +-------------------------+ 6.2.1.INVITEreceived WhenanINVITErequestisreceivedbythegateway,a"100Trying" responsemaybesentbacktotheSIPnetworkindicatingthattheMGC ishandlingthecall. Theresourcesforthemediastreamhavetobereservedatthisstage, sinceanIAMmessagecannotbesentbeforetheresourcereservation takesplace.Typicallytheresourcesconsistofatimeslotinan E1/T1andanRTP/UDPportontheIPside.Resourcesmightalso includeQoSor/andsecurityprovisions.BeforesendingtheIAMthe

Camarillo/Roach/Peterson/Ong[Page16] ISUPtoSIPMappingAugust2001 MGgenerallyconnectsthebackwardmediapath. AftersendingtheIAMthetimerT7isstarted.Thedefaultvalueof T7isbetween20and30seconds.TheMGCgoestothe`Trying'state. 6.2.1.1INVITEtoIAMprocedures ThissectiondetailsthemappingoftheSIPheadersinanINVITE

messagetotheISUPparametersinanIAM. FivemandatoryparametersappearwithintheIAMmessage:theCalled PartyNumber(CPN),theNatureofConnectionIndicator(NCI),the ForwardCallIndicators(FCI),theCallingParty'sCategory(CPC), andfinallyaparameterthatindicatesthedesiredbearer characteristicsofthecall-insomeISUPvariantstheTransmission MediumRequirement(TMR)isrequired,inotherstheUserService Information(USI)(orboth). TherearequiteafewoptionalparametersthatcanappearinanIAM message;Q.763[20]lists29inall.However,eachofthese parametersneednottobetranslatedinordertoachievethegoalsof SIP-ISUPmapping.Asisstatedabove,translationallowsSIPnetwork elementstounderstandthePSTNcontextofthesessioniftheyare notcapableofdecipheringanyencapsulatedISUP.Parametersthatare onlymeaningfultothePSTNwillbecarriedthroughPSTN-SIP-PSTN networksviaencapsulation-translationisnotnecessaryforthese parameters.Oftheaforementioned29optionalparameters,onlythe followingareimmediatelyusefulfortranslation:theCallingParty's Number(CIN,whichiscommonlypresent),TransitNetworkSelection (TNS),CarrierIdentificationParameter(CIP,presentinANSI networks),OriginalCalledNumber(OCN),andtheGenericDigits (knowninsomevariantsastheGenericAddressParameter(GAP)). WhenaSIPINVITEarrivesataPSTNgateway,thegatewayshould attempttomakeuseofanyencapsulatedISUP(see[4])toassistin theformulationofoutboundPSTNsignaling.However,threeconditions cancomplicatethisprocess: oThereisnoISUPencapsulatedintheSIPINVITE-theSIPINVITE originatedatadeviceotherthananISUP-SIPgateway. oThereisencapsulatedISUP,butthegatewaycannotunderstand theISUPvariantandthereforetheISUPmustbediscarded. oThereisencapsulatedISUP,butthereismorerecentsession contextinformationavailableintheSIPheaders,andconsequently theSIPheadersmust'overwrite'theencapsulatedISUP. Inallofthesecasestranslationmustbeperformed.Gatewaysshould usedefaultvaluesformandatoryISUPparametersthatarenotderived

Camarillo/Roach/Peterson/Ong[Page17] ISUPtoSIPMappingAugust2001 fromtranslationorencapsulation(suchastheNCIorTMR parameters).TheFCIparametershouldalsohaveadefault,although its'M'bitmaybeoverwrittenduringtheprocessoftranslation. First,theRequest-URIshouldbeinspected. Ifthereisno'npdi=yes'fieldwithintheRequest-URI,thenthemain telephonenumberinthetelURL(thedigitsimmediatelyfollowing 'tel:')shouldbeconvertedtoISUPformat,followingtheprocedure describedinsection11,andusedtopopulatetheCPNparameter.

InANSInetworks,ifthe'npdi=yes'fieldexistsintheRequest-URI, thentheFCIparameterbitfor'numbertranslated'withintheIAM shouldreflectthatanumberportabilitydiphasbeenperformed. Ifinadditiontothe'npdi=yes'fieldthereisno'rn='field present,thenthemaintelephonenumberinthetelURLshouldbe convertedtoISUPformat(seesection11)andusedtopopulatethe CPNparameter. Ifinadditiontothe'npdi=yes'fieldan'rn='fieldispresent, theninANSInetworksthe'rn='fieldshouldbeconvertedtoISUP formatandusedtopopulatetheCPN.Themaintelephonenumberinthe telURLshouldbeconvertedtoISUPformatandusedtopopulatethe GenericDigitsParameter(orGAPinANSI).Insomenetworksthe numbergiveninthe'rn='fieldshouldbeprependedtothemain telephonenumberandthecombinedresultshouldbeusedtopopulate theCPN. IfmaintelephonenumberintheRequest-URIandthatoftheToheader areatvariance,thentheToheadershouldbeusedtopopulateanOCN parameter.OtherwisetheToheadershouldbeignored. Ifthe'cic='parameterispresentintheRequest-URI,thegateway shouldconsultlocalpolicytomakesurethatitisappropriateto transmitthisCarrierIdentificationCodeintheIAM.Ifthegateway supportsmanyindependenttrunks,itmayneedtochooseaparticular trunkthatpointstothecarrieridentifiedbytheCIC,oratandem throughwhichthatcarrierisreachable.Policiesforsuchtrunks (basedonthepreferencesofthecarrierswithwhichthetrunksare associated)maydictatewhethertheCIPorTNSparametershouldbe used(althoughnotethatinnon-ANSInetworkstheCIPwillneverbe used).Intheabsenceofanypre-arrangedpolicies,theTNSshouldbe usedwhentheCPNparameterisinaninternationalformat(i.e.the NoAfieldoftheCPNindicatesthatthisisaninternationalnumber), andtheCIPshouldbeusedinothercases. IfaSIPcallhasarrivedatagateway,thentheRequest-URIwill

Camarillo/Roach/Peterson/Ong[Page18] ISUPtoSIPMappingAugust2001 mostlikelycontainatelURL(oraSIPURIwithatelURLuser portion).However,ifthecalloriginatedatanativeIPendpoint suchasaSIPphone,theFromfieldmaynotreflectanytelephone number-itmaybeasimpleuser@hostconstruction.TheCINparameter shouldbeomittedfromtheoutboundIAMiftheFromfieldis unusable. NotethatwhentheISUPparametersregardinginterworkingaresetin theForwardCallIndicators(FCI)parameteroftheIAM,this indicatesthatISDNisinterworkingwithanetworkwhichisnot capableofprovidingasmanyservicesasISDNdoes.ISUPwill thereforenotemploycertainfeaturesitotherwisenormallyuses. Thus,`interworkingencountered'mustnotbespecifiedsothatISUP

behavesnormally.SIPisconsideredasanSS7networkandaSIPphone isconsideredasISDNaccesssincetheSIPnetworkissupposedto provideatleastasmanyservicesasISUP. ClaimingtobeanISDNnodemightmakethecalleerequestISDNuser touserservices.Sinceusertouserservices1and2mustbe requestedbythecaller,theydonotrepresentaproblem[13].User touserservice3canberequestedbythecalleealso.Innon-SIP bridgingsituations,theMGCshouldbecapableofrejectingthis servicerequest. 6.2.2.ISUPT7expires SincenoresponsewasreceivedfromthePSTNalltheresourcesinthe MGarereleased.A`504gatewaytimeout'issentbacktotheSIP network.ARELmessagewithcausevalue102(protocolerror,recovery ontimerexpiry)issenttothePSTN.ThePSTNrespondswithRLCand theSIPnetworkrespondswithanACKindicatingthattherelease sequencehasbeencompleted. 6.2.3.CANCELorBYEreceived IfaCANCELorBYErequestisreceived,a`200OK'issenttotheSIP networktoconfirmtheCANCELorBYE;a487isalsosenttoterminate theINVITEtransaction.AlltheresourcesarereleasedandaREL messageissenttothePSTNwithcausevalue16(normalclearing).A RLCfromthePSTNisreceivedindicatingthatthereleasesequenceis complete. Itisimportantthatalltheresourcesarereleasedbeforethe gatewaysendsanyRELmessage. InSIPbridgingsituations,aRELmightarriveintheCANCELorBYE requestbody.ThisRELissenttothePSTN.

Camarillo/Roach/Peterson/Ong[Page19] ISUPtoSIPMappingAugust2001 Thissection(6.2.3.)applieseverytimethataCANCELoraBYEis receivedbeforeafinalSIPresponsehasbeensent. 6.2.4.RELreceived ThissectionapplieseverytimethataRELisreceivedbeforeafinal SIPresponsehasbeensent. TheresourcesarereleasedintheMGandaRLCissenttotheISUP networktoindicatethatthecircuitisavailableforreuse. IftheINVITEoriginatingthistransactioncontainedanISUPmessage initsbody(suchasanIAM),theMGCishandlingaSIPbridging situation.Therefore,theRELmessagejustreceivedshouldbe

includedinthebodyoftheresponse. Notethatthereceiptofcertainmaintenancemessagesinresponseto IAMsuchasBLOorRSC(ortheircircuitgroupmessageequivalents) mayalsoresultintheteardownofcallsinthisphaseofthestate machine.Behaviorformaintenancemessagesisgivenbelowinsection 10. 6.2.4.1ISDNCausecodetoSIPStatusCodemapping AnRELmessagecontainsanISDNCauseCode(see[16])intheCause Indicator(CAI)parameter.MostISUPvariants(includingANSIand ETSI)usethesecausecodestorepresentconditionssurroundingthe terminationofacall. InadditiontotheISDNCauseCode,theCAIparameteralsocontainsa cause'location'thatgivessomesenseofwhichentityinthenetwork wasresponsibleforterminatingthecall(themostimportant distinctionbeingbetweentheuserandthenetwork).Inmostcases, thecauselocationdoesnotaffectthemappingtoaSIPstatuscode; someexceptionsarenotedbelow.Adiagnosticfieldmayalsobe presentforsomeISDNcauses;thisdiagnosticwillcontainadditional datapertainingtotheterminationofthecall. TheuseoftheRELmessageintheSS7networkisverygeneral, whereasSIPhasanumberofspecifictoolsthat,collectively,play thesameroleasREL-namelyBYE,CANCEL,andthestatuscodes.An RELcanbesenttoteardownacallthatisalreadyinprogress (BYE),tocancelapreviouslysentcallsetuprequest(IAM)thathas notyetbeencompleted(CANCEL),ortorejectacallsetuprequest (IAM)thathasjustbeenreceived(correspondingtoaSIPstatus code). Ifacausevalueotherthanwhatislistedbelowisreceived,the

Camarillo/Roach/Peterson/Ong[Page20] ISUPtoSIPMappingAugust2001 defaultresponse`500Serverinternalerror'wouldbeused. NotethatitisnotnecessarilyappropriatetomapsomeISDNcause codestoSIPmessagesbecausethesecausecodesareonlymeaningful totheISUPinterfaceofagateway.Agoodexampleofthisiscause code44"Requestcircuitorchannelnotavailable."44signifiesthat theCircuitIdentificationCode(CIC)forwhichanIAMhadbeensent wasbelievedbythereceivingequipmenttobeinastateincompatible withanewcallrequest-however,theappropriatebehaviorinthis caseisfortheoriginatingswitchtore-sendtheIAMforadifferent CIC,notforthecalltobetorndown.Clearly,thereisnot(nor shouldtherebe)anSIPstatuscodeindicatingthatanewCICshould beselected-thismatterisinternaltotheoriginatinggateway. Hencereceiptofcausecode44shouldnotresultinanySIPstatus codebeingsent;effectively,thecausecodeisuntranslatable.

Normalevent ISUPCausevalueSIPresponse ---------------------------1unallocatednumber404NotFound 2noroutetonetwork404Notfound 3noroutetodestination404Notfound 16normalcallclearing---(*) 17userbusy486Busyhere 18nouserresponding408RequestTimeout 19noanswerfromtheuser480Temporarilyunavailable 20subscriberabsent480Temporarilyunavailable 21callrejected403Forbidden(+) 22numberchanged(w/odiagnostic)410Gone 22numberchanged(w/diagnostic)301MovedPermanently 23redirectiontonewdestination302MovedTemporarily 26non-selecteduserclearing404NotFound(=) 27destinationoutoforder502BadGateway 28addressincomplete484Addressincomplete 29facilityrejected501Notimplemented 31normalunspecified480Temporarilyunavailable (*)ISDNCause16willusuallyresultinaBYEorCANCEL (+)Ifthecauselocationis'user'thanthe6xxcodecouldbegiven ratherthanthe4xxcode(i.e.403becomes603) (=)ANSIprocedure-inANSInetworks,26isoverloadedto signify'misroutedportednumber'.Presumably,anumberportability dipshouldhavebeenperformedbyapriornetwork. ARELwithISDNcause22(numberchanged)mightcontaininformation aboutanewnumberwherethecalleemightbereachableinthe

Camarillo/Roach/Peterson/Ong[Page21] ISUPtoSIPMappingAugust2001 diagnosticfield.IftheMGCisabletoparsethisinformationit mightbeaddedtotheSIPresponse(301)inaContactheader. Resourceunavailable Thiskindofcausevalueindicatesanonpermanentsituation.A `Retry-After'headerhastobeaddedtotheresponse. ISUPCausevalueSIPresponse ---------------------------34nocircuitavailable503Serviceunavailable 38networkoutoforder503Serviceunavailable 41temporaryfailure503Serviceunavailable 42switchingequipmentcongestion503Serviceunavailable 47resourceunavailable503Serviceunavailable Serviceoroptionnotavailable

Thiskindofcausevalueindicatesapermanentsituation ISUPCausevalueSIPresponse ---------------------------55incomingcallsbarredwithinCUG403Forbidden 57bearercapabilitynotauthorized403Forbidden 58bearercapabilitynotpresently503Serviceunavailable available Serviceoroptionnotimplemented ISUPCausevalueSIPresponse ---------------------------65bearercapabilitynotimplemented501Notimplemented 79serviceoroptionnotimplemented501Notimplemented Invalidmessage ISUPCausevalueSIPresponse ---------------------------87usernotmemberofCUG503Serviceunavailable 88incompatibledestination503Serviceunavailable 95invalidmessage503Serviceunavailable Protocolerror

Camarillo/Roach/Peterson/Ong[Page22] ISUPtoSIPMappingAugust2001 ISUPCausevalueSIPresponse ---------------------------102recoveryoftimerexpiry408Requesttimeout 111protocolerror500Serverinternalerror Interworking ISUPCausevalueSIPresponse ---------------------------127interworkingunspecified500Serverinternalerror 6.2.5.EarlyACMreceived Thismessageissentincertainsituationsforresettingthetimers. Inthesecasesthismessageindicatesthatthecallisinprogress butcalleeisnotbeingalerted.Thisoccursforexampleinmobile networks,whereroamingcantakealongtime.TheearlyACMissent beforetheuserisalertedtoresetT7andstartT9.

AnACMisconsideredan`earlyACM'iftheCalledParty'sStatus Indicatorissetto00(noindication). AfterreceivinganearlyACMtheprogressofthecallisindicatedby thenetworksendingCPGs. Whenthereisinterworkingwithsomeoldsystems,itispossibleto receiveanANMimmediatelyafteranearlyACM(withoutCPG).Inthis situationtheSIPuserwillnothearanykindofringbacktonebefore thecalleeanswers.InISDN[11]thisissolvedbyconnectingthe voicepathbackwardsbeforesendingtheIAM. TheMGCsendsa183SessionProgress[9]totheSIPnetworkwitha mediadescriptioninside.InSIPbridgingsituationstheearlyACMis includedintheresponsebody.Thus,theproblemofmissingthering backtoneissolvedandtheearlyACMistransportedtransparently throughtheSIPnetwork. 6.2.6.ACMreceived UponreceptionofanACMtimerT9isstarted.T9typicallylasts between90secondsand3minutes[12].Itallowsthecallertohear announcementsfromthenetworkforthatperiodoftimewithoutbeing chargedfortheconnection.Iflongerannouncementshavetobeplayed thenetworkhastosendanANM.WhentheANMissentthecallbegins beingcharged.

Camarillo/Roach/Peterson/Ong[Page23] ISUPtoSIPMappingAugust2001 Thenearestlocalexchangetothecalleegeneratestheringbacktone andmaysendvoiceannouncements. UsuallyonreceiptofanACMa`180Ringing'issenttotheSIP network.Itshouldgenerallycontainasessiondescriptioninorder toallowSIPUAstopreventclippingofinitialcalleemedia.The ringbacktoneortheproperannouncementswillbegeneratedbythe PSTNexchange,andnotbythecallersSIPUAC/UAS. IftheBackwardsCallIndicator(BCI)parameteroftheACMindicates thatinterworkinghasbeenencountered(generallydesignatingthat theISUPnetworksendingtheACMisinterworkingwithaless sophisticatednetworkwhichcannotsupportcausecodes),thenthere maybein-bandannouncementsofcallstatussuchasanaudiblebusy toneorcallerinterceptmessage.Inthiscaseratherthana180 statuscode,a183SessionProgressmessageshouldbesentinorder toallowpre-ANMmediatoflowinthebackwardsdirection. InSIPbridgingsituations,theACMisincludedinthebodyofthe 180response. 6.2.7.CONorANMreceived

A`200OK'responseissenttotheSIPnetwork.InSIPbridging situations,theISUPmessageisincludedinthebodyofthe200OK response.Thisisalsothepointatwhichatwo-waymediastreamwill beestablished. 6.2.8.TimerT9expires ThisindicatesthattheANMhasnotarrivedintimespecified.This resultsinthecallbeingaborted.Alltheresourcesrelatedtothe mediapatharereleased.A`480temporarilyunavailable'issentto theSIPnetwork.ARELmessagewithcausevalue19(noanswerfrom theuser)issenttotheISUPpart.ThePSTNrespondswithRLCand theSIPnetworkrespondswithanACKindicatingthattherelease sequencehasbeencompleted. 6.2.9.CPGreceived ACPGcanindicateprogress,alertingorin-bandinformation.Ifthe CPGcomesafteranACM,thereisalreadyaone-wayvoicepathopen, sothereisnoneedoftakingfurtheractioninthemediapath. InSIPbridgingsituations,theCPGissentinthebodyofa18x response,determinedfromtheCPGeventcode. ISUPeventcodeSIPresponse

Camarillo/Roach/Peterson/Ong[Page24] ISUPtoSIPMappingAugust2001 ---------------------------1Alerting180Ringing 2Progress183Callprogress 3In-bandinformation183Callprogress 4Callforward;linebusy181Callisbeingforwarded 5Callforward;noreply181Callisbeingforwarded 6Callforward;unconditional181Callisbeingforwarded -(noeventcodepresent)183Callprogress Notethat,iftheCPGdoesnotindicate"Alerting,"thecurrentstate willnotchange. 6.2.10.ACKreceived Atthisstage,thecallisconnectedandtheconversationcantake place. 7.ISUPtoSIPmapping 7.1.CallFlows

Thefollowingcallflowsillustratetheorderofmessagesintypical successanderrorcaseswhensettingupacallinitiatedfromthe PSTNnetwork."100Trying"acknowledgementstoINVITErequestsare notexplained,sincetheirpresenceisoptional. Inthesediagrams,allcallsignaling(SIP,ISUP)isgoingtoand fromtheMGC;mediahandling(e.g.audiocut-through,trunkfreeing) isbeingperformedbytheMG,underthecontroloftheMGC.Forthe purposeofsimplicity,theseareshownasasinglenode,labeled "MGC/MG." 7.1.1.En-bloccallsetup(nonauto-answer) SIPMGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| |-----------100----------->|| 3|-----------18x----------->|| |==========Audio==========>|| ||=========================>| ||------------ACM---------->|4 5|<---------PRACK-----------|| 6|-----------200----------->|| 7|-----------18x----------->|| ||------------CPG---------->|8 9|<---------PRACK-----------||

Camarillo/Roach/Peterson/Ong[Page25] ISUPtoSIPMappingAugust2001 10|-----------200----------->|| 11|-----------200----------->|| |<=========Audio==========>|| ||------------ANM---------->|12 ||<=========Audio==========>| 13|<----------ACK------------|| (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnode. (3)Whenaneventsignifyingthatthecallhassufficient addressinginformationoccurs,theSIPnodewillgeneratea provisionalresponseof180orgreater. (4)Uponreceiptofaprovisionalresponseof180orgreater,the gatewaywillgenerateanACMmessage.Iftheresponseisnot 180,theACMwillcarrya"calledpartystatus"valueof"no

indication." (5)ThegatewaysendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (6)ThePRACKisconfirmed (7)TheSIPnodemayusefurtherprovisionalmessagestoindicate callprogress. (8)AfteranACMhasbeensent,allprovisionalresponseswill translateintoISUPCPGmessagesasindicatedin7.2.3. (9)ThegatewaysendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (10)ThePRACKisconfirmed (11)WhentheSIPnodeanswersthecall,itwillsenda200OK message. (12)Uponreceiptofthe200OKmessage,thegatewaywillsendan ANMmessagetowardstheISUPnode. (13)ThegatewaywillsendanACKtotheSIPnodetoacknowledge receiptoftheINVITEfinalresponse.

Camarillo/Roach/Peterson/Ong[Page26] ISUPtoSIPMappingAugust2001 7.1.2.Auto-answercallsetup SIPMGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| 3|-----------200----------->|| |<=========Audio==========>|| ||------------CON---------->|4 ||<=========Audio==========>| 5|<----------ACK------------|| (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnodebased oncallednumberanalysis. (3)SincetheSIPnodeissetuptoautomaticallyanswerthe call,itwillsenda200OKmessage.

(4)Uponreceiptofthe200OKmessage,thegatewaywillsenda CONmessagetowardstheISUPnode. (5)ThegatewaywillsendanACKtotheSIPnodetoacknowledge receiptoftheINVITEfinalresponse. 7.1.3.SIPTimeout SIPMGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| |***T1Expires***|| 3|<--------INVITE-----------|| |***T1Expires***|| |<--------INVITE-----------|| ||***T11Expires***| ||------------ACM---------->|4 |***T1Expires***|| |<--------INVITE-----------|| |***T1Expires***|| |<--------INVITE-----------|| |***T1Expires***|| |<--------INVITE-----------|| |***T1Expires***||

Camarillo/Roach/Peterson/Ong[Page27] ISUPtoSIPMappingAugust2001 |<--------INVITE-----------|| |***T1Expires***|| |**MGReleasesPSTNTrunk**| ||------------REL---------->|5 6|<--------CANCEL-----------|| ||<-----------RLC-----------|7 (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnodebased oncallednumberanalysis.TheISUPtimerT11andSIPtimer T1aresetatthistime. (3)TheINVITEmessagewillcontinuetobesenttotheSIPnode eachtimethetimerT1expires.TheSIPstandardspecifies thatINVITEtransmissionwillbeperformed7timesifno responseisreceived. (4)WhenT11expires,anACMmessagewillbesenttotheISUP nodetopreventthecallfrombeingtorndownbytheremotenode's ISUPT7.ThisACMcontainsa`CalledPartyStatus'valueof `noindication.'

(5)OncethemaximumnumberofINVITErequestshasbeensent,the gatewaywillsendaREL(causecode18)totheISUPnodeto terminatethe call. (6)ThegatewayalsosendsaCANCELmessagetotheSIPnodeto terminateanyinitiationattempts. (7)UponreceiptoftheREL,theremoteISUPnodewillsendan RLCtoacknowledge. 7.1.4.ISUPT9Expires SIPMGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| |***T1Expires***|| 3|<--------INVITE-----------|| |***T1Expires***|| |<--------INVITE-----------|| ||***T11Expires***|

Camarillo/Roach/Peterson/Ong[Page28] ISUPtoSIPMappingAugust2001 ||------------ACM---------->|4 |***T1Expires***|| |<--------INVITE-----------|| |***T1Expires***|| |<--------INVITE-----------|| |***T1Expires***|| |<--------INVITE-----------|| ||***T9Expires***| |**MGReleasesPSTNTrunk**| ||<-----------REL-----------|5 ||------------RLC---------->|6 7|<--------CANCEL-----------|| (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnodebased oncallednumberanalysis.TheISUPtimerT11andSIPtimer T1aresetatthistime. (3)TheINVITEmessagewillcontinuetobesenttotheSIPnode eachtimethetimerT1expires.TheSIPstandardspecifies thatINVITEtransmissionwillbeperformed7timesifno responseisreceived.SinceSIPT1startsat1/2secondor moreanddoubleseachtimeitisretransmitted,itwillbeat

leastaminutebeforeSIPtimesouttheINVITErequest;since SIPT1isallowedtobelargerthan500msinitially,itis possiblethat7xSIPT1willbelongerthanISUPT11+ISUP T9. (4)WhenT11expires,anACMmessagewillbesenttotheISUP nodetopreventthefrombeingtorndownbytheremotenode's ISUPT7.ThisACMcontainsa`CalledPartyStatus'valueof `noindication.' (5)WhenISUPT9intheremotePSTNnodeexpires,itwillsenda REL. (6)UponreceiptoftheREL,thegatewaywillsendanRLCto acknowledge. (7)TheRELwilltriggeraCANCELrequest,whichgetssenttothe SIPnode.

Camarillo/Roach/Peterson/Ong[Page29] ISUPtoSIPMappingAugust2001 7.1.5.SIPErrorResponse SIPMGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| 3|-----------4xx+---------->|| 4|<----------ACK------------|| |**MGReleasesPSTNTrunk**| ||------------REL---------->|5 ||<-----------RLC-----------|6 (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnodebased oncallednumberanalysis. (3)TheSIPnodeindicatesanerrorconditionbyreplyingwitha responsewithacodeof400orgreater. (4)ThegatewaysendsanACKmessagetoacknowledgereceiptof theINVITEfinalresponse. (5)AnISUPRELmessageisgeneratedfromtheSIPcode,as specifiedinsection7.2.6.

(6)TheremoteISUPnodeconfirmsreceiptoftheRELmessagewith anRLCmessage. 7.1.6.SIPRedirection SIPnode1MGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| 3|-----------3xx+---------->|| ||------------CPG---------->|4 5|<----------ACK------------|| || || SIPnode2|| 6|<--------INVITE-----------|| 7|-----------18x----------->|| |<=========Audio===========|| ||------------ACM---------->|8

Camarillo/Roach/Peterson/Ong[Page30] ISUPtoSIPMappingAugust2001 9|<---------PRACK-----------|| 10|-----------200----------->|| 11|-----------200----------->|| |<=========Audio==========>|| ||------------ANM---------->|12 ||<=========Audio==========>| 13|<----------ACK------------|| (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnodebased oncallednumberanalysis. (3)TheSIPnodeindicatesthattheresourcewhichtheuseris attemptingtocontactisatadifferentlocationbysendinga 3xxmessage. (4)ThegatewaysendsaCPGwitheventindicationthatthecall isbeingforwardeduponreceiptofthe3xxmessage.Notethat thistranslationshouldbeabletobedisabledby configuration,assomeISUPnodesdonotsupportreceiptof CPGmessagesbeforeACMmessages. (5)ThegatewayacknowledgesreceiptoftheINVITEfinalresponse bysendinganACKmessagetotheSIPnode. (6)Thegatewayre-sendstheINVITEmessagetotheaddress indicatedintheContact:fieldofthe3xxmessage.

(7)Whenaneventsignifyingthatthecallhassufficient addressinginformationoccurs,theSIPnodewillgeneratea provisionalresponseof180orgreater. (8)Uponreceiptofaprovisionalresponseof180orgreater,the gatewaywillgenerateanACMmessagewithaneventcodeas indicatedinsection7.2.3. (9)ThegatewaysendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (10)ThePRACKisconfirmed (11)WhentheSIPnodeanswersthecall,itwillsenda200OK message.

Camarillo/Roach/Peterson/Ong[Page31] ISUPtoSIPMappingAugust2001 (12)Uponreceiptofthe200OKmessage,thegatewaywillsendan ANMmessagetowardstheISUPnode. (13)ThegatewaywillsendanACKtotheSIPnodetoacknowledge receiptoftheINVITEfinalresponse. 7.1.7.CallCancelledbyISUP SIPMGC/MGPSTN ||<-----------IAM-----------|1 ||==========Audio==========>| 2|<--------INVITE-----------|| 3|-----------18x----------->|| |==========Audio==========>|| ||------------ACM---------->|4 5|<---------PRACK-----------|| 6|-----------200----------->|| |**MGReleasesPSTNTrunk**| ||<-----------REL-----------|7 ||------------RLC---------->|8 9|<---------CANCEL----------|| |**MGReleasesIPResources**| 10|-----------200----------->|| 11|-----------487----------->|| 12|<----------ACK------------|| (1)WhenaPSTNuserwishestobeginasessionwithaSIPuser, thePSTNnetworkgeneratesanIAMmessagetowardsthe gateway. (2)UponreceiptoftheIAMmessage,thegatewaygeneratesan INVITEmessage,andsendsittoanappropriateSIPnodebased oncallednumberanalysis.

(3)Whenaneventsignifyingthatthecallhassufficient addressinginformationoccurs,theSIPnodewillgeneratea provisionalresponseof180orgreater. (4)Uponreceiptofaprovisionalresponseof180orgreater,the gatewaywillgenerateanACMmessagewithaneventcodeas indicatedinsection7.2.3. (5)ThegatewaysendsaPRACKmessagetoconfirmreceiptofthe provisionalresponse. (6)ThePRACKisconfirmed (7)IfthecallingpartyhangsupbeforetheSIPnodeanswersthe

Camarillo/Roach/Peterson/Ong[Page32] ISUPtoSIPMappingAugust2001 call,aRELmessagewillbegenerated. (8)ThegatewayfreesthePSTNcircuitandindicatesthatitis availableforreusebysendinganRLC. (9)UponreceiptofaRELmessagebeforeanINVITEfinal response,thegatewaywillsendaCANCELtowardstheSIP node. (10)UponreceiptoftheCANCEL,theSIPnodewillsenda200 response. (11)TheremoteSIPnodewillsenda"487CallCancelled"to completetheINVITEtransaction. (12)ThegatewaywillsendanACKtotheSIPnodetoacknowledge receiptoftheINVITEfinalresponse. 7.2.StateMachine NotethatRELmayarriveinanystate.Wheneverthisoccurs,the actionsinsection7.2.7.aretaken.Notallofthesetransitionsare showninthisdiagram.

Camarillo/Roach/Peterson/Ong[Page33] ISUPtoSIPMappingAugust2001 +---------+ +----------------------->|Idle|<---------------------+ |+----+----+| ||| ||IAM/7.2.1| |V| |REL/7.2.7+-------------------------+400+/7.2.6| +<----------------+Trying|------------>| |+-+--------+------+-------+| ||||| ||T11/|18x/|200/| ||7.2.8|7.2.3|7.2.4| |V||| |REL/7.2.7+--------------+||400+/7.2.6| |<----------|Progressing|-|------|-------------------->| |+--+----+------+||| |||||| |200/||18x/||| |7.2.4||7.2.3||| ||VV|| |REL/7.2.7|+---------------+|400+/7.2.6| |<-------------|--|Alerting|-|-------------------->| ||+--------+------+|| ||||| |||200/|| |||7.2.4|| |VVV| |BYE/9.1+-----------------------------+REL/9.2| +<------------+Connected+------------>+ +-----------------------------+ 7.2.1.InitialAddressMessagereceived UponthereceptionofanIAM,resourcesarereservedinthemedia gatewayanditconnectsaudiointhebackwardsdirection(towardsthe caller).

7.2.1.1IAMtoINVITEprocedures WhenanIAMarrivesataPSTN-SIPgateway,aSIPINVITEmessagewill becreatedfortransmissiontotheSIPnetwork.Thissectiondetails theprocessbywhichagatewaypopulatestheINVITEbasedon parametersfoundwithintheIAM. ThesessioncontextinformationdiscoveredbythegatewayintheIAM willbestoredprimarilyintwoURIsintheINVITE,onerepresenting theoriginatorofthesessionandtheotherthedestination.The formerwillalwaysappearintheFromheader(afterithasbeen

Camarillo/Roach/Peterson/Ong[Page34] ISUPtoSIPMappingAugust2001 convertedfromISUPformatbytheproceduredescribedinsection11), andthelatterisalmostalwaysusedforboththeToheaderandthe Request-URI. TheconstructionofdestinationURIbeginswithdeterminingwhich ISUPparametercurrentlycontainsthecalledpartynumber.Usually, thiswillbetheCPNparameter.However,ifthedestinationnumber hasbeenported(see[x])andadiptotherelevantLNPdatabasehas alreadybeenperformed,thenthecalledpartynumberwill,insome ISUPvariantsincludeANSI,infactappearintheGenericDigits ParameterorGAP.Generallyinsuchvariantsthe'numbertranslated' bitoftheFCIparametershouldbeconsultedtodeterminewhetherthe calledpartynumberisintheCPNparameterortheGAPparameter.In othervariants,ifaportabilitydiphasbeenperformedtherouting numbermaybefoundedprependedtothecalledpartynumberintheCPN parameter. Oncethelocationofthecalledpartynumberhasbeendetermined,it shouldbetranslatedintoatelURLthroughthemechanismdescribed above.SomeadditionalfieldsmayneedtobeaddedtothetelURL aftertranslationhasbeencompleted,namely: oIf(inANSInetworks)theFCI'numbertranslated'bitindicated thatanLNPdiphadbeenperformed,or(inothervariants)ifa routingnumberhasbeenprependedtotheCPN,thenan'npdi=yes' fieldmustbeappendedtothetelURL.Iftheroutingnumberisnot presentintheCPN,thenifaGenericDigitsParameter(orGAPin ANSI)ispresentintheIAM,thenthecontentsoftheCPNshouldbe translatedfromISUPformat(asdescribedabove)andcopiedintoan 'rn='fieldwhichmustbeappendedtothetelURL.Notethat LocationRoutingNumbers(LRNs)storedinCPNforcallstoported numbersarenecessarilynationalinscope,andconsequentlythey willnotbeprecededbya'+'inthe'rn='field.Forfurther informationonthesetelURLfieldssee[17]. oIfeithertheCIP(inANSInetworks)orTNSispresent,the carrieridentificationcode(CIC)shouldbeextractedfromthe parameterandanalyzedbythegateway.Ifdoingsoisinkeeping withlocalpolicy(i.e.providedthattheCICdoesnotindicate

thenetworkwhichownsthegatewayorsomesimilarcondition),a 'cic='fieldwiththevalueoftheCICshouldbeappendedtothe telURL.NotethattheCICshouldbeprefixedwiththecountrycode usedorimpliedinthecalledpartynumber,sothatCIC'5062' becomes,intheUnitedStates,'+1-5062'.Forfurtherinformation onthe'cic='telURLfieldsee[17]. Inmostcases,theresultingURIshouldbeusedintheTofieldand Request-URIsentbythegateway.However,iftheOCNparameteris

Camarillo/Roach/Peterson/Ong[Page35] ISUPtoSIPMappingAugust2001 presentintheIAM,theTofieldconstructedfromthetranslationof theOCNparameter,andhencetheRequest-URIandTofieldwillbe different. TheconstructionoftheFromfieldisdependentonthepresenceofa CINparameter.IftheCINisnotpresent,thenthegatewayshould createadummyFromheadercontainingaSIPURIwithoutauser portionwhichcommunicatesonlythehostnameofthegateway(e.g. 'sip:gw.level3.net').IftheCINisavailable,thenitshouldbe translated(inaccordancewiththeproceduredescribedabove)intoa telURLwhichshouldpopulatetheFromfield. 7.2.2.100received A100responsedoesnottriggeranyPSTNinterworkingmessages;it onlyservesthepurposeofsuppressingINVITEretransmissions. 7.2.3.18xreceived IfnoACMhasbeensentyetandnoISUPispresentinthe18xmessage body,andISUPmessageisgeneratedaccordingtothefollowingtable. Notethat,ifanearlyACMissent,thecallentersstate "Progressing"insteadofstate"Alerting." ResponsereceivedMessagesentbytheMGC ---------------------------------------180RingingACM 181CallisbeingforwardedEarlyACMandCPG,event=6 182QueuedACM 183SessionprogressmessageACM IfanACMhasalreadybeensentandnoISUPispresentinthe18x messagebody,anISUPmessageisgeneratedaccordingtothefollowing table. ResponsereceivedMessagesentbytheMGC ---------------------------------------180RingingCPG,event=1(Alerting) 181CallisbeingforwardedCPG,event=6(Forwarding) 182QueuedCPG,event=2(Progress)

183SessionprogressmessageCPG,event=2(Progress) Ifthereceptionofa`180Ringing'responsewithoutmedia description,theMGgeneratestheringbacktonetobeheardbythe caller. IftheMGCreceivesany1xxresponse(except100)withasession descriptionpresentformediasetup,itsetsupthesessionbeing

Camarillo/Roach/Peterson/Ong[Page36] ISUPtoSIPMappingAugust2001 described.Thecallprogressmedia(e.g.ringbacktoneor announcement)isgeneratedbyanentitydownstream(intheSIP networkorbyaPSTNexchangeinSIPbridgingsituations). IfanACMhasnotbeensentyet,oneisgeneratedandsent.The mandatoryparametersoftheACMaredescribedbelow: Messagetype:ACM BackwardIndicators Chargeindicator:10charge Calledparty'sstatusindicator:01subscriberfreeor 00noindication(E.ACM) Calledparty'scategoryindicator:01ordinarysubscriber End-to-endmethodindicator:00noend-to-endmethod Interworkingindicator:0nointerworking End-to-endinformationindicator:0noend-to-endinfo ISDNuserpartindicator:1ISUPalltheway Holdingindicator:0noholding ISDNaccessindicator:1ISDNaccess Echocontroldeviceindicator:Itdependsonthecall SCCPmethodindicator:00noindication InSIPbridgingsituationstheMGCsendstheISUPmessagecontained intheresponsebody. Notethatsending183beforeagatewayhasconfirmationthatthe addressiscomplete(ACM)createsknownproblemsinSIPbridging cases,anditshouldthereforebeavoided. 7.2.4.200received ResponsereceivedMessagesentbytheMGC ---------------------------------------200OKANM,ACK Afterreceivinga200OKresponsetheMGCestablishesatwo-wayvoice pathintheMGanditsendsanANMtothePSTNandanACKtotheSIP network. Ifthe`200OK'responsearrivesbeforetheMGChassenttheACM,a CONissentinsteadoftheANM.

InSIPbridgingsituationstheMGCsendstheANMortheCONinthe responsebody.

Camarillo/Roach/Peterson/Ong[Page37] ISUPtoSIPMappingAugust2001 7.2.5.3xxreceived Whenany3xxresponseisreceived,theMGCshouldtrytocontactthe userusingthe`Contact'headerorheaderspresentintheresponse. These3xxresponsesaretypicallysentbyare-directserver.Thisis asimilardevicetotheHLRinmobilenetworks.Itprovidesanother addresswherethecalleemaybereached. ACPGmessagewithaneventcodeof2(Progress)maybesentto indicatethatthecallisproceeding.NotethatsomeISUPnodesmay notsupportCPGbeforeACM,sothisfeatureshouldbeconfigurable. IfthenewlocationpresentedintheContactheaderofa3xxisbest reachable(accordingtothegateway'sroutingpolicies)viathePSTN, theMGCsendsanewIAMandfromthatmomentonactsasanormalPSTN switch(noSIPinvolved).Ifthenewlocationisbestreachableusing SIP,theMGCsendsanINVITEwithpossiblyanewIAMgeneratedbythe MGCinthemessagebody. Allredirectionsituationshavetobetreatedverycarefullybecause theyinvolvedspecialchargingsituations.InPSTNthecaller typicallypaysthefirstcalllegandthecalleepaysthesecond. 7.2.6.4xx-6xxreceived TheMGCreleasestheresourcesintheMG,sendaRELtothePSTNwith acausevalueandsendanACKtotheSIPnetwork.AnRLCarrives indicatingthatthereleasesequenceiscomplete. 7.2.6.1SIPStatusCodetoISDNCauseCodemapping Bydefault,thecauselocationassociatedwiththeCAIparameter shouldbeencodedsuch6xxcodesaregiventhelocation'user', whereas4xxand5xxcodesaregivena'network'location.Exceptions aremarkedbelow. AnySIPstatuscodesnotlistedbelow(associatedwithSIP extensions,versionsofSIPsubsequenttotheissueofthisdocument, orsimplyomitted)shouldbemappingtocausecode31"Normal, unspecified". JustastherearecertainISDNcausecodesthatareISUP-specificand

havenocorollarySIPaction,sothereareSIPstatuscodesthat shouldnotbetranslatedtoISUP.Examplesareflaggedwith(+) below. ResponsereceivedCausevalueintheREL ---------------------------------------

Camarillo/Roach/Peterson/Ong[Page38] ISUPtoSIPMappingAugust2001 401Unauthorized21Callrejected(*) 402Paymentrequired21Callrejected 403Forbidden21Callrejected 404Notfound1Unallocatednumber 405Methodnotallowed63Serviceoroption unavailable 406Notacceptable79Service/optionnot implemented 407Proxyauthenticationrequired21Callrejected(*) 408Requesttimeout102Recoveryontimerexpiry 409Conflict48Temporaryfailure 410Gone22Numberchanged (w/odiagnostic) 411Lengthrequired127Interworking(+) 413RequestEntitytoolong127Interworking(+) 414Request-URItoolong127Interworking(+) 415Unsupportedmediatype79Service/optionnot implemented(+) 420Badextension127Interworking(+) 480Temporarilyunavailable18Nouserresponding 483Toomanyhoops25Exchange-routingerror 484Addressincomplete28InvalidNumberFormat(+) 485Ambiguous1Unallocatednumber 486Busyhere17Userbusy 488NotAcceptablehere---byWarningheader 500Serverinternalerror41Temporaryfailure 501Notimplemented38Networkoutoforder 502Badgateway38Networkoutoforder 503Serviceunavailable41Temporaryfailure 504Servertime-out102Recoveryontimerexpiry 600Busyeverywhere17Userbusy 603Decline21Callrejected 604Doesnotexistanywhere1Unallocatednumber 606Notacceptable---byWarningheader (*)Insomecases,itmaybepossibleforaSIPgatewaytoprovide credentialstotheSIPUASthatisrejectinganINVITEdueto authorizationfailure.Ifthegatewaycanauthenticateitself,then obviouslyitshoulddosoandproceedwiththecall;onlyifthegateway cannotauthorizeitselfshouldcausecode21besent. (+)Ifatallpossible,aSIPgatewayshouldrespondtotheseprotocol errorsbyremedyingunacceptablebehaviorandattemptingtore-originate thesession.OnlyifthisprovesimpossibleshouldtheSIPgatewayfail theISUPhalfofthecall.

WhentheWarningheaderispresentinaSIP606or488message,there maybespecificISDNcausecodemappingsappropriatetotheWarning

Camarillo/Roach/Peterson/Ong[Page39] ISUPtoSIPMappingAugust2001 code.Thisdocumentassumesthatsending'31Normal,unspecified' willbesufficientforallcurrentlyassignedWarningcodes. 7.2.7.RELreceived TheMGCshouldaborttheestablishmentofthesession.ACANCEL requesthastobeissued.ABYEisnotused,sincenofinalresponse hasarrivedfromtheSIPside.A200OKfortheCANCELarrives,anda 487fortheINVITEarrives. TheMGChastostorestateinformationforacertainperiodoftime, sincea200finalresponsefortheINVITEoriginallysentmight arrive(evenafterthereceptionofthe200OKfortheCANCEL).In thissituation,theMGCsendsanACKandthenaBYE. InSIPbridgingsituations,theRELmessagemaybeincludedinthe CANCELmessagebody.CANCELrequestsareansweredwithafinal response(suchas200OK)bythefirstproxy.Therefore,theMGCdoes notknowiftheCANCELhasarrivedtotheenduser(egressMGCin thisscenario).Hence,ifa200OKresponseforthepreviouslysent INVITEarrivestheMGCsendsanACKandthenaBYEwiththeRELin themessagebody. 7.2.8.ISUPT11Expires InordertopreventtheremoteISUPnode'stimerT7fromexpiring, thegatewaymaychoosetokeepitsownsupervisorytimer;ISUP definesthistimerasT11.T11'sdurationiscarefullychosensothat itwillalwaysbeshorterthantheT7ofanynodetowhichthe gatewayiscommunicating. ToclarifytimerT11'srelevancewithrespecttoSIPinterworking, Q.764[14]explainsitsuseas:"Ifinnormaloperation,adelayin thereceiptofanaddresscompletesignalfromthesucceedingnetwork isexpected,thelastcommonchannelsignalingexchangewill originateandsendanaddresscompletemessage15to20seconds [timer(T11)]afterreceivingthelatestaddressmessage."SinceSIP nodeshavenoobligationtorespondtoanINVITErequestwithin20 seconds,SIPinterworkinginarguablyqualifiesassuchasituation. Ifthegateway'sT11expires,itwillsendanearlyACM(i.e.called partystatussetto"noindication")topreventtheexpirationofthe remotenode'sT7.Seesection7.2.3.forthevalueoftheACM parameters. Ifa"180Ringing"messagearrivessubsequently,itwillbesentina

CPG,asshowninsection7.2.3.

Camarillo/Roach/Peterson/Ong[Page40] ISUPtoSIPMappingAugust2001 See7.1.3.foranexamplecallflowthatincludestheexpirationof T11. 8.Suspend/Resumeandhold 8.1.SUSandRES InISDNnetworks,ausercangenerateaSUS(timerT2,user initiated)inordertounplugtheterminalfromthesocketandplug itinanotherone.ARESissentoncetheterminalhasbeen reconnectedandtheT2timerhasnotexpired. WhenaSUSarrivesfromthePSTN,theMGCshouldsendanINVITEto putthemediastreamonhold.ThereceptionofaREStriggersareINVITEthatresumesthemediastream.FortheSIPUAC/UAStheresult isaninterruptioninthevoicepathuntiltheotherpartypicksup thephoneagain.Puttingthemediaonholdinsuresthatbandwidthis conservedwhennoaudiotrafficneedstobetransmitted. Insomeinstancesitmaybeundesirabletoputthemediaforacall onholdwhenaSUSisreceived.Intheseinstancesare-INVITEshould stillbeusedtocarrytheSUSmessage;however,theSDPwithinthe INVITEshouldrepeatthelastSDPgivenratherthansubstitutingthe 'null'SDPusedtoputcallsonhold(i.e.inwhichthec=lineor portinthem=lineindicates'0'). InSIPbridgingsituations,theSUSandRESmessagescanbe transferredinthebodyoftheINVITE. SIPMGC/MGPSTN ||<-----------SUS-----------|1 2|<--------INVITE-----------|| 3|-----------200----------->|| 4|<----------ACK------------|| ||<-----------RES-----------|5 6|<--------INVITE-----------|| 7|-----------200----------->|| 8|<----------ACK------------|| Thehandlingofanetwork-initiatedSUSimmediatelypriortocall teardownishandledinsection9.2.2. 8.2.Hold(re-INVITE) Afteracallhasbeenconnected,are-INVITEmaybesenttoagateway fromtheSIPsideinordertoplacethecallonhold.Thisre-INVITE

willhaveanSDPindicatingthattheoriginatorofthere-INVITEno longerwishestoreceivemedia.

Camarillo/Roach/Peterson/Ong[Page41] ISUPtoSIPMappingAugust2001 SIPMGC/MGPSTN 1|---------INVITE---------->|| ||------------CPG---------->|2 3|-----------200----------->|| 4|<----------ACK------------|| Whensuchare-INVITEisreceived,thegatewayshouldsendaCall ProgressMessage(CPG)inordertoexpressthatthecallhasbeen placedonhold.TheCPGshouldcontainaGenericNotification Indicator(or,inANSInetworks,aNotificationIndicator)witha valueof'remotehold'. Ifsubsequenttothesendingofthere-INVITEtheSIPsidewishesto taketheremoteendoffhold,andtobeginreceivingmediaagain,it mayrepeattheflowabovewithanINVITEthatcontainsanSDPwitha reachablemediadestination.TheGenericNotificationIndicatorwould inthisinstancehaveavalueof'remoteretrieval'(orinsome variants'remoteholdreleased'). Finally,notethataCPGwithholdindicatorsmaybereceivedbya gatewayfromthePSTN.Intheinterestsofconservingbandwidth,the gatewaymaywishtostopsendingmediauntilthecallisresume, and/orsendare-INVITEtotheSIPlegofthecallrequestingthat theremotesidestopsendingmedia. 9.NormalReleaseoftheConnection EithertheSIPsideortheISUPsidemayreleaseacall,regardless ofwhichsideinitiatedthecall. 9.1.SIPinitiated Foranormalreleaseofthecall(receptionofBYE),theMGC immediatelysendsa200response.Itthenreleasestheresourcesin theMGandsendsanRELwithacausecodeof16(normalcall clearing)tothePSTN.ReleaseofresourcesisconfirmedbythePSTN withaRLC. InSIPbridgingsituations,theRELcontainedintheBYEissentto thePSTN. SIPMGC/MGPSTN 1|-----------BYE----------->|| |**MGReleasesIPResources**| 2|<----------200------------|| |**MGReleasesPSTNTrunk**| ||------------REL---------->|3

||<-----------RLC-----------|4

Camarillo/Roach/Peterson/Ong[Page42] ISUPtoSIPMappingAugust2001 9.2.ISUPInitiated Ifthereleaseoftheconnectionwascausedbythereceptionofa REL,theRELisincludedintheBYEsentbytheMGC. 9.2.1.Callerhangsup Foranormalreleaseofthecall(receptionofRELfromthePSTN), theMGCfirstreleasestheresourcesintheMGandthenconfirmsthat theyarereadyforre-usebysendinganRLC.TheSIPconnectionis releasedbysendingaBYE(whichisconfirmedwitha200). SIPMGC/MGPSTN ||<-----------REL-----------|1 |**MGReleasesPSTNTrunk**| ||------------RLC---------->|2 3|<----------BYE------------|| |**MGReleasesIPResources**| 4|-----------200----------->|| 9.2.2.Calleehangsup InanalogPSTN,ifthecalleehangsupinthemiddleofacall,the localexchangesendsaSUSinsteadofaRELandstartsatimer(T6, SUSisnetworkinitiated).Whenthetimerexpires,theRELissent. SIPMGC/MGPSTN ||<-----------SUS-----------|1 2|<--------INVITE-----------|| 3|-----------200----------->|| 4|<----------ACK------------|| ||***T6Expires***| ||<-----------REL-----------|5 |**MGReleasesPSTNTrunk**| ||------------RLC---------->|6 7|<----------BYE------------|| |**MGReleasesIPResources**| 8|-----------200----------->|| 10.ISUPmaintenancemessages ISUPcontainsasetofmessagesusedformaintenancepurposes.They canbereceivedduringanongoingcall.Therearebasicallytwokinds ofmaintenancemessages(apartfromthecontinuitycheck):message forblockingcircuitsandmessagesforresettingcircuits.

Camarillo/Roach/Peterson/Ong[Page43] ISUPtoSIPMappingAugust2001 10.1.Resetmessages Uponreceptionofaresetmessageforthecircuitbeingused,the callhastobereleased.RSCmessagesareansweredwithRLCafter resettingthecircuitintheMG.GRSmessagesareansweredwithGRA afterresettingallthecircuitsaffectedbythemessage. TheMGCactsasifaRELhadbeenreceivedinordertoreleasethe connectionontheSIPside.Thesessionwillbeterminated.ABYEor aCANCELaresentdependingofthestatusofthecall. 10.2.Blockingmessages Therearetwokindsofblockingmessages:maintenanceorientedor hardwarefailureoriented.Maintenanceorientedblockingmessages indicatesthatthecircuithastobeblockedforsubsequentcalls. Therefore,thesemessagesdonotaffectanyongoingcall. Hardwareorientedblockingmessageshavetobetreatedasreset messages.Thecallisreleased. BLOisalwaysmaintenanceorientedanditisansweredbytheMGCwith BLAwhenthecircuitisblocked.CGBmessageshavea"typeindicator" insidethe"circuitgroupsupervisionmessagetypeindicator".It indicatesiftheCGBismaintenanceorhardwarefailureoriented. CGBsareansweredwithCGBAs. 10.3ContinuityChecks Acontinuitycheckisatestperformedonacircuitthatinvolvesthe reflectionofatonegeneratedattheoriginatingswitchbya loopbackatthedestinationswitch.Twovariantsofthecontinuity checkappearinISUP:theimplicitcontinuitycheckrequestwithinan IAM(inwhichcasethecontinuitychecktakesplacebeforecallsetup begins),andtheexplicitcontinuitychecksignaledbyaContinuity CheckRequest(CCR)message. WhenaCCRisreceivedbyaPSTN-SIPgateway,thegatewayshouldnot sendanySIPmessages;thescopeofthecontinuitycheckappliesonly tothePSTNtrunks,nottoanyIPmediapaths. WhenanIAMwiththeContinuityCheckIndicatorflagsetwithinthe NatureofConnectionIndicators(NCI)parameterisreceived,the gatewayshouldprocessthecontinuitycheckbeforesendinganINVITE message;ifthecontinuitycheckfails(aCOTwithContinuity Indicatorof'failed'isreceived),thenanINVITEshouldnotbe

sent.

Camarillo/Roach/Peterson/Ong[Page44] ISUPtoSIPMappingAugust2001 11.ConstructionofTelephonyURIs SIPproxyserversmayrouteSIPmessagesonanysignalingcriteria desiredbynetworkadministrators,butgenerallytheRequest-URIis theforemostroutingcriterion.TheToandFromheadersarealso frequentlyofinterestinmakingroutingdecisions.SIP-ISUPmapping assumesthatproxyserversareinterestedinatleastthesethree fieldsofSIPmessages,allofwhichcontainURIs. SIP-ISUPmappingfrequentlyrequirestherepresentationoftelephone numbersintheseURIs.Insomeinstancesthesenumberswillbe presentedfirstinISUPmessages,andSS7-SIPgatewayswillneedto translatetheISUPformatsofthesenumbersintoSIPURIs.Inother casesthereversetransformationwillberequired. ThemostcommonformatusedinSIPfortherepresentationof telephonenumbersisthetelURL,definedin[18].ThetelURLmay constitutetheentiretyofaURIfieldinaSIPmessage,oritmay appearastheuserportionofaSIPURI.Forexample,aTofield mightappearas: To:tel:+17208881000 Or To:sip:[email protected] WhetherornotaparticulargatewayorendpointshouldformulateURIs inthetelorSIPformatisamatteroflocaladministrativepolicyifthepresenceofahostportionwouldaidthesurroundingnetwork inroutingcalls,theSIPformatshouldbeused.Agatewayshould accepteithertelorSIPURIsfromitspeers. The'+'signprecedingthenumberintheseexamplesindicatesthat thedigitswhichfollowconstituteafully-qualifiedE.164[19] number;essentially,thismeansthatacountrycodeisprovided beforeanynational-specificareacodes,exchange/citycodes,or addresscodes.Theabsenceofa'+'signcouldmeanthatthenumber isnationallysignificant,orperhapsthataprivatedialingplanis inuse.Whenthe'+'signisnotpresent,butatelephonenumberis representedbytheuserportionoftheURI,theSIPURIshould containtheoptional';user=phone'parameter;e.g. To:sip:[email protected];user=phone However,itishighlyrecommendedthatonlyinternationally significantE.164numbersbepassedbetweenSIP-Tgateways, especiallywhensuchgatewaysareindifferentregionsordifferent

Camarillo/Roach/Peterson/Ong[Page45] ISUPtoSIPMappingAugust2001 administrativedomains.InmanyifnotmostSIP-Tnetworks,gateways arenotresponsibleforend-to-endroutingofSIPcalls;practically speaking,gatewayshavenowayofknowingifthecallwillterminate inalocalorremoteadministrativedomainand/orregion,andhence gatewaysshouldalwaysassumethatcallsrequireaninternational numberingplan.ThereisnoguaranteethatrecipientsofSIP signalingwillbecapableofunderstandingnationaldialingplans usedbytheoriginatorsofcalls-iftheoriginatinggatewaydoes notinternationalizethesignaling,thecontextinwhichthedigits weredialedcannotbeextrapolatedbyfar-endnetworkelements. InISUPsignaling,atelephonenumberappearsinacommonformatthat isusedinseveralparameters,includingtheCalledParty'sNumber (CPN)andCallingParty'sNumber(CIN);whenitrepresentsacalling partynumberitsportssomeadditionalinformation(detailedbelow). Forthepurposesofthisdocument,wewillrefertothisformatas 'ISUPformat'-iftheadditionalcallingpartyinformationis present,theformatshallbereferredtoas'ISUP-callingformat'. TheformatconsistsofabytecalledtheNatureofAddress(NoA) indicator,followedbyanotherbytewhichcontainstheNumberingPlan Indicator(NPI),bothofwhichareprefixedtoavariable-length seriesofbytesthatcontainsthedigitsofthetelephonenumberin binarycodeddecimal(BCD)format.Inthecallingpartynumbercase, theNPI'sbytealsocontainsbitfieldswhichrepresentthecaller's presentationpreferencesandthestatusofanycallscreeningchecks performedupuntilthispointinthecall. HGFEDCBAHGFEDCBA +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+ ||NoA|||NoA| +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+ ||NPI|spare|||NPI|PrI|ScI| +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+ |dig...|dig1||dig...|dig1| |...||...| |dign|dig...||dign|dig...| +-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+ ISUPformatISUPcallingformat Figure1.ISUPnumberingformats TheNPIfieldisgenerallysettothevalue'ISDN(Telephony) numberingplan(RecommendationE.164)',butthisdoesnotmeanthat thedigitswhichfollownecessarilycontainacountrycode;theNoA fielddictateswhetherthetelephonenumberisinanationalor internationalformat.Whentherepresentednumberisnotdesignated

Camarillo/Roach/Peterson/Ong[Page46] ISUPtoSIPMappingAugust2001 tobeinaninternationalformat,theNoAgenerallyprovides informationspecifictothenationaldialingplan-basedonthis informationonecanusuallydeterminehowtoconvertthenumberin questionintoaninternationalformat.NotethatiftheNPIcontains avalueotherthan'ISDNnumberingplan',thenthetelURLmaynotbe suitableforcarryingtheaddressdigits,andthehandlingforsuch callsisoutsidethescopeofthisdocument. Basedontheabove,conversionfromISUPformattoatelURLisas follows.First,providedthattheNPIfieldindicatesthatthe telephonenumberformatusesE.164,theNoAshouldbeconsulted.If theNoAindicatesthatthenumberisaninternationalnumber,then thetelephonenumberdigitsshouldbeappendedunmodifiedtoa 'tel:+'string.IftheNoAhasthevalue'national(significant) number',thenacountrycodemustbeprefixedtothetelephonenumber digitsbeforetheyarecommittedtoatelURL;ifthegateway performingthisconversioninterconnectswithswitcheshomedto severaldifferentcountrycodes,presumablytheappropriatecountry codeshouldbechosenbasedontheoriginatingswitch.IftheNoAhas thevalue'subscribernumber',bothacountrycodeandanyother numberingcomponentsnecessaryforthenumberingplaninquestion (suchasareacodesorcitycodes)mayneedtobeaddedinorderfor thenumbertobeinternationallysignificant-however,such proceduresvarygreatlyfromcountrytocountry,andhencethey cannotbespecifiedindetailhere.OnlyifacountryornetworkspecificvalueisusedfortheNoAshouldatelURLnotincludea'+' sign;inthesecases,gatewaysshouldsimplycopytheprovideddigits intothetelURLandappenda'user=phone'parameterifaSIPURI formatisused.Anynon-standardorproprietarymechanismsusedto communicatefurthercontextforthecallinISUPareoutsidethe scopethisdocument. Ifanationally-specificparameterispresentthatallowsforthe transmissionofthecallingparty'sname(suchastheGenericName ParameterinANSI),thengenerally,ifpresentationisnot restricted,thisinformationshouldbeusetopopulatethedisplaynameportionoftheFromfield. IfISUPcallingformatisusedratherthanISUPformat,thentwo additionalpiecesofinformationmustbetakenintoaccount: presentationindicatorsandscreeningindicators.Ifthepresentation indicatorsaresetto'presentationrestricted',thenaspecialURI shouldbecreatedbythegatewaywhichcommunicatestothefarend thatthecaller'sidentityhasbeenelided.ThisURIshouldbeaSIP URIwiththehostnameofthegatewaybutwithadisplaynameof 'Anonymous'usernameof'restricted',e.g.:

Camarillo/Roach/Peterson/Ong[Page47]

ISUPtoSIPMappingAugust2001 From:Anonymous Asfurthergeneral-purposeprivacymechanismsaredevelopedforthe SIPprotocol,theymayalsobeusedtoprotecttheidentityofa caller. Ifpresentationissetto'addressunavailable',thengatewaysshould treattheIAMasiftheCINparameterwasomitted.Screening indicatorsshouldnotbetranslated,astheyareonlymeaningfulendto-end. ConversionfromtelURLstoISUPformatissimpler.IftheURIisin internationalformat,thenthegatewayshouldconsulttheleading countrycodeoftheURI.Ifthecountrycodeislocaltothegateway (thegatewayhasoneormoretrunksthatpointtoswitcheswhichare homedtothecountrycodeinquestion),thegatewayshouldsetthe NoAtoreflect'national(significant)number'andstripthecountry codefromtheURIbeforepopulatingthedigitsfield.Ifthecountry codeisnotlocaltothegateway,thegatewayshouldsettheNoAto 'internationalnumber'andretainthecountrycode.Ineithercase theNPIshouldbesetto'ISDNnumberingplan'. IftheURIisnotininternationalformat,thegatewayshouldattempt totreatthetelephonenumberwithintheURIasifitwere appropriatetoitsnationalornetwork-specificdialingplan;if doingsogivesrisetointernalgatewayerrors,thenthiscondition ismostlikelybesthandledwithappropriateSIPstatuscodes(e.g. 484). WhenconvertingfromatelURLtoISUPcallingformat,theprocedure isidenticaltothatdescribedintheprecedingparagraphs,but additionally,thepresentationindicatorshouldbesetto 'presentationallowed'andthescreeningindicatorto'network provided',unlesssomeserviceproviderpolicyoruserprofile specificallydisallowspresentation. 12.OtherISUPflavors OtherflavorsofISUPdifferentthanQ.767[2]havemoreparameters andmorefeatures.Someoftheparametershavemorepossiblevalues andprovidemoreinformationaboutthestatusofthecall. TheCircuitQueryMessage(CQM)andCircuitQueryResponse(CQR)are usedinmanyISUPvariants.ThesemessageshavenoanaloginSIP, althoughreceiptofaCQRmaycausestatereconciliationifthe originatinganddestinationswitcheshavebecomedesynchronized;as statesarereconciledsomecallsmaybedropped,whichmaycauseSIP orISUPmessagestobesent.

Camarillo/Roach/Peterson/Ong[Page48] ISUPtoSIPMappingAugust2001

However,differencesinthemessageflowsaremoreimportant.InANSI ISUP[3],thereisnoCONmessage;anANMissentinstead(withno ACM).Incallforwardingsituations,CPGscanbesentbeforetheACM issent.SAMsareneverused;`enbloc'signalingisalwaysused.The ANSIExitMessage(EXM)shouldnotresultinanySIPsignalingin gateways.ANSIalsousestheCircuitReservationMessage(CRM)and CircuitReservationAcknowledgment(CRA)aspartofitsinterworking procedures-althoughaSIPgatewayshouldnoteverreceivethese messages,ifitdoesreceivesuchamessagethereisnoappropriate SIPactiontobetaken(therecommendedbehaviorissendingaRELin responsetotheCRM). AlthoughreceiptofaConfusion(CFN)messageisanindicationofa protocolerror,noSIPmessageshouldbesentonreceiptofaCFNtheCFNshouldbehandledinternallybythegateway(usuallyby retransmissionofthepackettowhichtheCFNresponded).Onlyif thisfailsrepeatedlyshouldthiscauseaSIPerrorconditionto arise. InTTCISUPCPGscanbesentbeforetheACMissent.Messagessuchas CHGcanbesentbetweenACMandANM.`Enbloc'signalingisalways usedandthereisnoT9timer. 12.1.GuidelinestosendotherISUPmessages SomeISUPflavorssendmoremessagesthantheonesdescribedinthis document.Itisgoodtofollowsomeguidelinestotransportthese ISUPmessagesinsideSIPbodies. FromthecallertothecalleeISUPmessagesshouldbeencapsulated (see[4])insideINFOmessages,eveniftheINVITEtransactionis stillnotfinished.NotethatSIPdoesnotensurethatINFOrequests aredeliveredinorder.Therefore,anegressgatewaymightprocess firstanINFOrequestthatwassentafteranotherINFOrequest.This issue,however,doesnotrepresentanimportantproblemsinceitis notlikelytohappenanditseffectsarenegligibleinmostofthe situations.TheInformation(INF)messageandInformationResponse (INR)areexamplesofmessagesthatshouldbeencapsulatedwithinan INFO. NotethatifanINRisreceivedbeforecallestablishmentiscomplete (i.e.ANMisreceived)itshouldbeencapsulatedinaanINFO,rather thananyprovisional1xxresponse.SimilarlyanINFisreceivedon theoriginatingside(probablyinreponsetoanINR)beforea200has beenreceivedshouldbecarriedwithinanINFO.Inorderforthis mechanismtofunctionproperlyintheforwarddirection,any necessaryContactorTo-tagmusthaveappearedinaprevious provisionalresponseorthemessagemightnotbecorrectlyroutedto

Camarillo/Roach/Peterson/Ong[Page49] ISUPtoSIPMappingAugust2001 itsdestination.AssuchallSIP-Tgatewaysshouldsendprovisional

responseswithaContactheaderandanynecessarytagsinorderto enableproperroutingofnewrequestsissuedbeforeafinalresponse hasbeenreceived. ISUPmessagesfromthecalleetothecallershouldbesentinside provisionalresponses.SIPensuresthatprovisionalresponses transmittedreliablyaredeliveredinorder.WhentheINVITE transactionisfinishedINFOrequestsshouldbeusedalsointhis direction. 13.Acronyms ACKAcknowledgment ACMAddressCompleteMessage ANMAnswerMessage ANSIAmericanNationalStandardsInstitute BLABlockingACKmessage BLOBlockingMessage CGBCircuitGroupBlockingMessage CGBACircuitGroupBlockingACKMessage CHGChargingInformationMessage CONConnectMessage CPGCallProgressMessage CUGClosedUserGroup GRACircuitGroupResetACKMessage GRSCircuitGroupResetMessage HLRHomeLocationRegister IAMInitialAddressMessage IETFInternetEngineeringTaskForce IPInternetProtocol ISDNIntegratedServicesDigitalNetwork ISUPISDNUserPart ITU-TInternationalTelecommunicationUnion TelecommunicationStandardizationSector MGMediaGateway MGCMediaGatewayController MTPMessageTransferPart RELReleaseMessage RESResumeMessage RLCReleaseCompleteMessage RTPReal-timeTransportProtocol SCCPSignalingConnectionControlPart SGSignalingGateway SIPSessionInitiationProtocol SS7SignalingSystemNo.7 SUSSuspendMessage TTCTelecommunicationTechnologyCommittee

Camarillo/Roach/Peterson/Ong[Page50] ISUPtoSIPMappingAugust2001 UACUserAgentClient UASUserAgentServer UDPUserDatagramProtocol

VoIPVoiceoverIP 14.Acknowledgments TheauthorswouldliketothankOlliHynonen,TomasMecklin,Bill Kavadas,JonathanRosenberg,HenningSchulzrinne,TakuyaSawada, MiguelA.Garcia,IgorSlepchin,DouglasC.Sicker,SamHoffpauir, Jean-FrancoisMule,ChristerHolmberg,DougHurtig,TahirGun,and JanVanGeelfortheirhelpandfeedbackonthisdocument. 15.RevisionHistory Changesfromdraft-ietf-sip-isup-00: -Mergeddraft-jfp-sip-isup-header-00intothisdraft -Removedoverlapsignalingcomponent(now draft-ietf-sip-overlap-00) -Adjustedcausecodetostatuscodemappings Changesfromdraft-ietf-sip-isup-01: -Addedproceduresforplacingcallsonhold -GeneralizedlanguageandproceduresforLNP,removingANSIbias -Fixedusageof'user=phone' -AddedhandlingforSegmentationMessageinISUP -UpdatedSUS/REShandlingtouseINFOconsistently(ratherthan 183) Changesfromdraft-ietf-sip-isup-02: -FixedsomemoreANSI-specificreferences(GNI,screening) -Fixedtimerexpirycausecodevalues(6.2.2) -Removedsomebis04incompatibilities(6.2.10) -Addedmotivationaltexttoabstractandintroduction

Camarillo/Roach/Peterson/Ong[Page51] ISUPtoSIPMappingAugust2001 16.References [1]M.Handley,H.Schulzrinne,E.Schooler,J.Rosenberg,"SIP:

SessionInitiationProtocol",RFC2543,IETF;March1999. [2]"ApplicationoftheISDNuserpartofCCITTsignalingsystem No.7forinternationalISDNinterconnections"ITU-TQ.767 recommendation,February1991. [3]"SignalingSystemNo.7;ISDNUserPart"T1.113-1995ANSI. January1995. [4]EZimmerer,J.Peterson,A.Vemuri,L.Ong,F.Audet,M. Watson,M.Zonoun,"MIMEmediatypesforISUPandQSIG Objects",InternetDraft, IETF;April2001.Workinprogress. [5]N.Freed,N.Borenstein,"MultipurposeInternetMail Extensions(MIME)PartTwo:MediaTypes",RFC2046,IETF; November1996. [6]H.Schulzrinne,S.Petrack,"RTPPayloadforDTMFDigits, TelephonyTonesandTelephonySignals",RFC2833,IETF;May 2000. [8]J.Rosenberg,H.Schulzrinne,"ReliabilityofProvisional ResponsesinSIP",InternetDraft, IETF;March2001.Workinprogress. [9]M.Handley,H.Schulzrinne,E.Schooler,J.Rosenberg,"SIP: SessionInitiationProtocol",InternetDraft ,IETF;August2001.Workin progress. Formerreferenceplaceholderfor183work: S.Donovan,M.Cannon,H.Schulzrinne,J.Rosenberg,A.Roach, "SIP183SessionProgressMessage",InternetDraft,IETF October1999.(expiredI-D) [10]StevenR.Donovan,"TheSIPINFOMethod",RFC2976,IETF; February2000. [11]"SignalingSystemNo.7;ISDNUserPartSignaling procedures",ITU-TQ.764recommendation,September1997. [12]Abnormalconditions-SpecialreleaseITU-TQ.118 recommendation,September1997.

Camarillo/Roach/Peterson/Ong[Page52] ISUPtoSIPMappingAugust2001 [13]"SpecificationsofSignalingSystemNo.7-ISDN supplementaryservices"ITU-TQ.737recommendation,June 1997. [14]"SpecificationsofSignalingSystemNo.7-ISDNUserPart SignalingProcedures"ITU-TQ.764recommendation,March

1993. [15]R.Stewartetal,"StreamControlTransmissionProtocol". RFC2960,IETF;October2000. [16]"UsageofcauselocationintheDigitalSubscriberSignaling SystemNo.1andtheSignalingSystemNo.7ISDNUserPart"ITU-T Q.850Recommendation,May1998 [17]J.Yu,"Extensionstothe'tel'and'fax'URLstoSupportNumber PortabilityandFreephoneService",Internet-Draft ,IETF,Feb2001.(Workinprogress) [18]A.Vaha-Sipila,"URLsforTelephoneCalls",RFC2806,IETF,April 2000. [19]"Theinternationalpublictelecommunicationnumberplan",ITU-T E.164Recommendation,May1997 [20]"FormatsandcodesoftheISDNUserPartofSignalingSystemNo. 7",ITU-TQ.763recommendation,March1993. 17.SecurityConsiderations ThetransitofISUPinSIPbodiesmayprovidemayopportunitiesfor abuseandfraud.Inparticular,SIPusersmaybeabletointerpret "private"(i.e.caller-id-blocked)numbersbyexaminingtheISUP. Similarly,ifcareisnottaken,SIPclientswouldbeabletosend ISUPmessagesintotheSS7networkwithinvalidcallingline identificationandspoofedbillingnumbers. Forthesereasons,itisabsolutelynecessarythatanyISUPsent throughanIPnetworkbestronglyencryptedandauthenticated.The keysusedforencryptionshouldnotbestatic,topreventreplay attacks.Achallenge-responsemodelisrecommended.Asanextralayer ofsecurity,itisrecommendedthatISUPbesentandreceivedonlyto andfromnodesthatareknowntohaveanestablishedtrust relationshipwiththegateway.

Camarillo/Roach/Peterson/Ong[Page53] ISUPtoSIPMappingAugust2001 18.Authors'Addresses GonzaloCamarillo Ericsson AdvancedSignallingResearchLab FIN-02420Jorvas Finland

Phone:+35892993371 Fax:+35892993052 Email:[email protected] AdamRoach EricssonInc. MailstopL-04 851InternationalPkwy. Richardson,TX75081 USA Phone:+1972-583-7594 Fax:+1972-669-0154 E-Mail:[email protected] JonPeterson NeuStar,Inc 1800SutterStreet,Suite570 Concord,CA94520 USA Phone:+19253638700 E-Mail:[email protected] LyndonOng Ciena 10480RidgeviewCourt Cupertino,CA95014 E-Mail:[email protected] FullCopyrightStatement Copyright(c)TheInternetSociety(2001).AllRightsReserved. Thisdocumentandtranslationsofitmaybecopiedandfurnishedto others,andderivativeworksthatcommentonorotherwiseexplainitor assistinitsimplementationmaybeprepared,copied,publishedand distributed,inwholeorinpart,withoutrestrictionofanykind, providedthattheabovecopyrightnoticeandthisparagraphareincluded onallsuchcopiesandderivativeworks.However,thisdocumentitself maynotbemodifiedinanyway,suchasbyremovingthecopyrightnotice orreferencestotheInternetSocietyorotherInternetorganizations, exceptasneededforthepurposeofdevelopingInternetstandardsin

Camarillo/Roach/Peterson/Ong[Page54] ISUPtoSIPMappingAugust2001 whichcasetheproceduresforcopyrightsdefinedintheInternet Standardsprocessmustbefollowed,orasrequiredtotranslateitinto languagesotherthanEnglish. Thelimitedpermissionsgrantedaboveareperpetualandwillnotbe revokedbytheInternetSocietyoritssuccessorsorassigns. Thisdocumentandtheinformationcontainedhereinisprovidedonan"AS IS"basisandTHEINTERNETSOCIETYANDTHEINTERNETENGINEERINGTASK FORCEDISCLAIMSALLWARRANTIES,EXPRESSORIMPLIED,INCLUDINGBUTNOT