A SIP INVITE is a SIP request message that initiates a SIP call. A SIP INVITE is made up of lines of text. The first line in an INVITE is called a ...
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ASIPINVITEisaSIPrequestmessagethatinitiatesaSIPcall.
ASIPINVITEismadeupoflinesoftext.ThefirstlineinanINVITEiscalledaRequest-Line,whichisfollowed bymorelinesoftextcalled"headers".TheheaderscontaininformationabouttheINVITE,suchastheidentityofthecaller,whethertheINVITEwasforwardedbeforebeingsenttotherecipient,andthenumberoftimesacallmaybeforwarded.
TableofContents:
ExampleSIPINVITE
SIPURIs
SIPUser
SIPHostorSIPDomain
SIPPort
SIPRequest-Line
Request-URI
CommonSIPINVITEHeaders
Viaheader
Max-Forwardsheader
Toheader
Fromheader
Call-IDheader
CSeqheader
Contactheader
Diversionheader
P-Asserted-Identityheader
OtherSIPINVITEHeaders
Remote-Party-Id(RPID)header
P-Charge-Infoheader
ExampleSIPINVITE
BelowisanexampleofaSIPINVITErequestmessage,whichincludessomecommonly-usedSIPINVITEheaders.
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
SIPURIs
IntheINVITEabove,youcanseeseveralexamplesofwhatarecalledSIPURIsthatlooklikee-mailaddresses.ASIPURIidentifiesausers'contactinformationbyindicatingaspecificuserataspecifichost/domain.ASIPURIcouldbeanidentifierforaspecificperson,avoicemailbox,agroupwithinanorganization(like"sales"or"marketing"),etc.
sip:[email protected]
ThepartsofaSIPURIaredescribedbelow.
SIPUser
Theuserisaphonenumber,word,orusernamethatsitsbetweenthesip:andthe@inaSIPURI.
sip:[email protected]
sip:[email protected]
sip:[email protected]
SIPHostorSIPDomain
Thehostordomainfollowsthe@inaSIPURIandcanbeadomainorIPaddress.
sip:[email protected]
sip:[email protected]
SIPPort
ASIPURIcanalsocontainaportnumber.Itiswrittenaftera:followingthehost.IfnoportisincludedintheSIPURI,thedefaultSIPport5060isused.
sip:[email protected]:6000
SIPRequest-Line
ASIPINVITEisatypeofSIPrequest.ThefirstlineinanySIPrequestiscalledtheRequest-Line.
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheRequest-Linecontainsthreeparts:
Therequestmethodname:
INVITEsip:[email protected]/2.0
TheRequest-URI:
INVITEsip:[email protected]/2.0
TheSIPprotocolversion:
INVITEsip:[email protected]/2.0
Request-URI
TheRequest-URIisthecontactinformationfortherecipientoftheSIPINVITE.ItisfoundwithintheRequest-LineoftheINVITE.
TheRequest-URI:
INVITEsip:[email protected]/2.0
TheRequest-URIUser:
INVITEsip:[email protected]/2.0
TheRequest-URIHost:
INVITEsip:[email protected]/2.0
CommonSIPINVITEHeaders
SIPheaderscontaininformationabouttheSIPmessage.
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheSIPheadersinaSIPrequestfollowtheRequest-Line.
ASIPheaderhasanameandavalue.Theheadernameisbeforethecolon(:),theheadervalueiswhatfollowsthecolon.Fortheheaderonline7above,theheaderwouldbecalledthe"CSeqheader",andvalueoftheCSeqheaderis1INVITE.
Viaheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
Thisheaderfielddescribesthetransportusedforthetransaction(SIP/2.0/UDP)andidentifieswhereresponsesshouldbesent(to192.168.10.10onport5060).ThebranchparameterisauniquevalueusedtoidentifythetransactionthatiscreatedbytheSIPrequest.
Max-Forwardsheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
Thisheaderlimitsthenumberofhopsarequestcanmakeonthewaytoitsdestination.Thevalueisanintegerthatdecreasesbyoneateachhop.IfthevalueoftheMax-Forwardsheaderreaches0beforetheSIPrequestreachesitsdestination,therequestwillberejectedwitha483error(TooManyHops).
Toheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheToheadercontainsthecontactinformationforthecalledparty(therecipientoftheSIPINVITE).
Todisplayname:
To:“Bob”
ToURI:
To:“Bob”
Touser:
To:“Bob”
Tohost:
To:“Bob”
Fromheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheFromheadercontainsthecontactinformationforthepartythatinitiatedtheSIPINVITE.
Fromdisplayname:
From:“Alice”;tag=1
FromURI:
From:“Alice”;tag=1
Fromuser:
From:“Alice”;tag=1
Fromhost:
From:“Alice”;tag=1
Call-IDheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheCall-IDheaderactsasauniqueidentifierthathelpsgroupaseriesofmessagestogether.Itmustbethesameforallrequestsandresponsessentbyeitherpartyinadialog(anexchangeofrelatedmessagesbetweentwouser-agents).Thevalueshouldbeacryptographicallyrandomgroupofcharacters,andcanbefollowedby@andahost/domain.
CSeqheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheCSeqheaderservesasawaytoidentifyandordertransactions.ItismadeupofanintegerandaSIPmethod.
Contactheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheContactheaderprovidesaSIPorSIPSURIthatshouldbeusedtocontacttheuseragentthatsenttheINVITE.
Contactdisplayname:
Contact:"Alice"
ContactURI:
Contact:“Alice”
Contactuser:
Contact:“Alice”
Contacthost:
Contact:“Alice”
Diversionheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheDiversionheadercontainsinformationaboutanyre-directing/forwardingthecallhasundergone.Itincludesthecontactinformationforthepartythatforwardedthecall.
Diversiondisplayname:
Diversion:"Sales"
DiversionURI:
Diversion:“Sales”
Diversionuser:
Diversion:“Sales”
Diversionhost:
Diversion:“Sales”
P-Asserted-Identityheader
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDP192.168.10.10:5060;branch=z9hG4bK776asdhds
Max-Forwards:70
To:"Bob"
From:"Alice";tag=1
Call-ID:a84b4c76e66710
CSeq:1INVITE
Contact:"Alice"
Diversion:"Sales"
P-Asserted-Identity:"Alice"
Content-Length:0
TheP-Asserted-IdentityheadercontainstheCallerIDinformationforthecallthatwasauthenticatedinsomeway.Thisheadermaybeusedwhenforwardingcallswithintrusteddomains,inordertomaintaintheoriginalcaller'scallerIDratherthantheforwardingentity's.
P-Asserted-Identitydisplayname:
P-Asserted-Identity:"Alice"
P-Asserted-IdentityURI:
P-Asserted-Identity:“Alice”
P-Asserted-Identityuser:
P-Asserted-Identity:“Alice”
P-Asserted-Identityhost:
P-Asserted-Identity:“Alice”
OtherSIPINVITEHeaders
Remote-Party-Id(RPID)header
Remote-Party-Id:“Alice”
TheRemote-Party-Id(RPID)headeridentifiestheoriginatorofthecall.
Remote-Party-Id(RPID)displayname:
Remote-Party-Id:"Alice"
Remote-Party-Id(RPID)URI:
Remote-Party-Id:“Alice”
Remote-Party-Id(RPID)user:
Remote-Party-Id:“Alice”
Remote-Party-Id(RPID)host:
Remote-Party-Id:“Alice”
P-Charge-Infoheader
P-Charge-Info:“Alice”
TheP-Charge-Infoheadercontainsinformationabouttheidentityofthepartytobecharged.
P-Charge-Infodisplayname:
P-Charge-Info:"Alice"
P-Charge-InfoURI:
P-Charge-Info:“Alice”
P-Charge-Infouser:
P-Charge-Info:“Alice”
P-Charge-Infohost:
P-Charge-Info:“Alice”
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