The Beginner's Guide to SIP Headers - Telnyx

A SIP Header is a component of a SIP message that is used to convey information about the SIP message. Including the correct SIP Header and ... BacktoblogSIPmessagerequestsarecriticaltosuccessfullyutilizingSIPtrunkingtechnology.Useragentsandnetworkserversusemessagerequeststolocate,invite,andmanagecalls.SIPmessagerequestsuseSIPheaderstosupplyinformationabouttherequestedactionorinformation.WhynottryoutourSIPTrunkingproductandseeforyourselfhowSIPheaderswork?YoucansetupaTelnyxPortalaccountinminutes&receive$10offreetestingcredit.WhatisaSIPHeader?ASIPHeaderisacomponentofaSIPmessagethatisusedtoconveyinformationabouttheSIPmessage.IncludingthecorrectSIPHeaderandcorrectlyformattingtheseSIPHeadersiscriticaltoensurethatrequestsaresuccessfullyroutedtotherightrecipients.We'lltryandrunthroughsomeofthemostcommonSIPHeadersinthisblogpost.HeadersfortheStandardSIPCallUsually,anINVITEmessageinitiatesasession—essentiallyaphonecall—ontheSIPprotocol.WhiletherearemanyotherSIPheaders,thenineoutlinedbelowsupplytheminimumrequiredinformationtoinitiateacalloveraSIPtrunkingnetwork.ABYErequestisusedtoterminatecalls.ToTheToheaderspecifiestherecipientofthecall.Format1To:“(name)”CopyViaTheViaheaderidentifiesacall’spathwiththeprotocolname,protocolversion,transporttype,useragentclient(UAC),theprotocolportfortherequestandabranchparameterwhichservesasauniqueidentifierforeachSIPtransaction.TheViaheaderroutesSIPresponsestothecorrectdevice,similartoareturnaddressonapackage.IfaSIPrequestisroutedthroughmultipledevices,eachUACaddsitsownVIAheadertotherequestbeforesendingiton.Format1Via:SIP/(protocolversion)/(transporttype)(UAC):(protocolport);branch=(branchnumber)CopyCall-IDTheCall-IDSIPHeadercreatesagloballyuniqueidentifierforthecall.ToensurethateachCall-IDidentifierisgloballyunique,arandomnumberisgenerated(whichoftenlookslikethis:f_169eac17a017b0a4e0adfa8_I),andthesender’sIPaddressisappendedtothisnumber.ThisguaranteesthattheCall-IDnumberwillbegloballyunique,sincenotwodeviceswillhavethesameIPaddress.Format1Call-ID:(generatednumber)@(ip\_address)CopyContactTheContactheaderidentifiesthemostdirectrouteforsendingfuturerequeststotherequestingdevice.TheContactheaderspecifiesacallerdomainnameorIPaddressandatransporttype.Format1Contact:sip:(user)@(domain);transport=(transporttype)CopyFromTheFromheaderspecifieswhothecalliscomingfrom.Format1From:“(name)”CopyContent-LengthTheContent-Lengthheaderspecifiesthesizeofthemessagecontentinbytes.AContent-Lengthof0indicatesthatthereisnomessagebody.Format1Content-Length:(numberofbytesinmessagebody)CopyCSeqTheCSeqheaderspecifiesthenumberofrequestsofeachtypethathavebeensent.Forexample,CSeq:15INVITEmeansthatisthe15thinviterequest.Thenumberincreasesbyoneforeachadditionalrequestofthesametype.Format1CSeq:(number)(requesttype)CopyMax-ForwardsTheMax-Forwardsheaderlimitsthenumberoftimesarequestcanbeforwardedonitswaytotherecipient.Thenumberisreducedbyoneeachtimetherequestisforwarded.TheMax-ForwardsheaderpreventsarequestfromendlesslycirclingtheSIPnetworkiftherecipientcannotbefound.Thedefaultvalueis70.Format1Max-Forwards:(maximumnumberofforwards)CopyContent-TypeIfthemessagehasabody,theContent-Typeheaderidentifieshowthebodyisformatted.Atextmessagemightbeidentifiedastext/HTMLoranapplicationmakingacallmightidentifythecontentasapplication/SDP.Format1Content-Type:(typeofcontent)CopyGuidelinesforSIPHeadersBelowarearesometipsandbestpracticesthatyoucanfollowtomakethemostofSIPheaders.Formorein-depthinformation,reachouttoourteamofexperts.Headerscanbeplacedinanyorder.However,theessentialheadersshouldbelistedfirst.TheREQUESTlineistechnicallynotaheaderandalwaysgoesfirst.Keepheadersasshortaspossible.Compactheaderscanbeusedforevenshorterheaders.Forexample:HeaderCompactFormToTViaVCall-IDIConatctMFromFSubjectSContactLengthLIfyou’reusingapoint-to-pointSIPclient,anIPaddressmustbeusedinplaceofa[email protected]identifier.UtilizeWiresharktocaptureSIPpacketsforanalysisornetworkdiagnostics-it'sfree!StillconfusedaboutSIPtrunking?Readourbeginner'sguideforeverythingyouneedtoknow,orchattoourexpertstofindouthowSIPtrunkingcanmakeyourphonesystemcheaperandmoreflexiblethaneverbefore.ShareonSocialSetupSIPtrunkinginlessthan10minutesSignupRelatedPosts5ThingsforPoSDeviceVendorstoConsiderin2022aSIMcardandtheindustrywords"mPOS""checkoutexperience"and"Bigtech"areshownontheleftEasilybuildvoicecallingintoyourapplicationBuildtheno-fussvideosolutionyou'vealwayswantedTelnyxandIterablePartnerforGlobalMessagingEmployeeSpotlight:NatashaTomattisClaimOffer