SIP is a widely adopted application layer protocol used in VoIP calls and confernecing applciations and in IMS architeture or pure packet switched networks ...
Skiptocontent
SIPisawidelyadoptedapplicationlayerprotocolusedinVoIPcallsandconfernecingapplciationsandinIMSarchitetureorpurepacketswitchednetworks.
MoreonSIP,itspacketstructure,transactionanddialogs,looseandstrictrecordrouting,locationservice,nearandfarendnating,andcommonlyusedSIPCallflowslikeRedirection,forking,clicktoDial–https://telecom.altanai.com/2013/07/13/sip-session-initiaion-protocol/(opensinanewtab)
SIPRequestandRepsosnes
TraditionalSIPheadersforCallsetupareINVITE,ACKandteardownareCANCELorBYE,howeverwithmoreadoptionnewermethodsspecifictoserviceswereaddedsuchas:
MESSAGEMethodsforInstantMessagebasedservicesSUBSCRIBE,NOTIFYstandardisedbyEventnotificationextensionRFC3856PUBLISHtopushpresenceinformationtothenetwork
OutliningtheSIPRequestsandResponsesintablesbelow,
RequestMessage
RequestMessageDescriptionREGISTERAClientusethismessagetoregisteranaddresswithaSIPserverINVITEAUserorServiceusethismessagetoletanotheruser/serviceparticipateinasession.Thebodyofthismessagewouldincludeadescriptionofthesessiontowhichthecalleeisbeinginvited.ACKThisisusedonlyforINVITEindicatingthattheclienthasreceivedafinalresponsetoanINVITErequestCANCELThisisusedtocancela pendingrequestBYEAUserAgentClientusethismessagetoterminatethecallOPTIONSThisisusedtoqueryaserveraboutitscapabilities
ResponseMessage
CodeCategoryDescription1xxProvisionalTherequesthasbeenreceivedandprocessingiscontinuing2xxSuccessAnACK,toindicatethattheactionwassuccessfullyreceived,understood,andaccepted.3xxRedirectionFurtheractionisrequiredtoprocessthisrequest4xxClientErrorTherequestcontainsbadsyntaxandcannotbefulfilledatthisserver5xxServerErrorTheserverfailedtofulfillanapparentlyvalidrequest6xxGlobalFailureTherequestcannotbefulfilledatanyserver
SIPheaders
Displaynames
Fromoriginatorssipuri
CSeqorCommandSequencecontainsanintegerandamethodname.TheCSeqnumberisincrementedforeachnewrequestwithinadialogandisatraditionalsequencenumber.
Contact–SIPURIthatrepresentsadirectroutetotheoriginatorusuallycomposedofausernameatafullyqualifieddomainname(FQDN),alsoIPaddressesarepermitted.TheContactheaderfieldtellsotherelementswheretosendfuturerequests.
Max-Forwards-tolimitthenumberofhopsarequestcanmakeonthewaytoitsdestination.Itconsistsofanintegerthatisdecrementedbyoneateachhop.
Content
Content-Type–descriptionofthemessagebody.
Content-Type:application/h.323
Content-Type:message/sip
Content-Type:application/sdp
Content-Type:multipart/signed;
protocol="application/pkcs7-signature";
micalg=sha1;boundary=boundary42
Content-Type:application/pkcs7-signature;name=smime.p7s
ContentEncoding
Content-Encoding:text/plain
ContentLanguage
Content-Language:en
Content-Length–anoctet(byte)countofthemessagebody.
Content-Disposition
describeshowthemessagebodyor,formultipartmessages,amessagebodypartistobeinterpretedbytheUACorUAS.ItextendstheMIMEContent-Type
DispositionTypes:
“session”–bodypartdescribesasession,foreithercallsorearly(pre-call)media“render”–bodypartshouldbedisplayedorotherwiserenderedtotheuser.“icon”–bodypartcontainsanimagesuitableasaniconicrepresentationofthecallerorcallee“alert”–bodypartcontainsinformation,suchasanaudioclip
Accept
Accept–acceptableformatslikeapplication/sdporcurrency/dollars
HeaderfieldwhereproxyACKBYECANINVOPTREG
AcceptR-o-om*oAccept2xx---om*oAccept415-c-ccc
AnemptyAcceptheaderfieldmeansthatnoformatsareacceptable.
Accept-Encoding
Accept-EncodingR-o-oooAccept-Encoding2xx---om*oAccept-Encoding415-c-ccc
Accept-Language:languagesforreasonphrases,sessiondescriptions,orstatusresponsescarriedasmessagebodiesintheresponse.
Accept-Language:da,en-gb;q=0.8,en;q=0.7
Accept-LanguageR-o-ooo
Accept-Language2xx---om*o
Accept-Language415-c-ccc
Taggloballyuniqueandcryptographicallyrandomwithatleast32bitsofrandomness.identifyadialog,whichisthecombinationoftheCall-IDalongwithtwotags(fromToandFROMheaders)
Call-Iduniquelyidentifyasession
contact–sipurlalternativefordirectrouting
Encryption
Expires–whenmsgcontentisnolongervalid
MandatorySIPheaders
INVITEsip:[email protected]/2.0
Via:SIP/2.0/UDPhost.domain.com:5060
From:Bob
To:Altanai
Call-ID:[email protected]
CSeq:1INVITE
Informationalheaders
Call-Infoadditionalinformationforexample,throughawebpage.The“card”parameterprovidesabusinesscard,forexample,invCard[36]orLDIF[37]formats.AdditionaltokenscanberegisteredusingIANA
Call-Info:http://wwww.example.com/alice/photo.jpg;purpose=icon,http://www.example.com/alice/;purpose=info
ContactContact:“Mr.Watson”;q=0.7;expires=3600,“Mr.Watson”[email protected];q=0.1m:;expires=60
Priorityindicatestheurgencyoftherequestasperceivedbytheclient.canhavethevalues“non-urgent”,“normal”,“urgent”,and“emergency”,butadditionalvaluescanbedefinedelsewhere
Subject:Atornadoisheadingourway!Priority:emergency
or
Subject:WeekendplansPriority:non-urgent
Subjectsummaryorindicatesthenatureofcall
Subject:Needmoreboxess:TechSupport
Supportedenumeratesalltheextensionssupported.cancontainlistofoptiontags,described
Supported:100relk:100rel
Unsupportedfeaturesnotsupported
Unsupported:foo
User-AgentinformationabouttheUACoriginatingtherequest.
User-Agent:SoftphoneBeta1.5
OrganizationconveysthenameoftheorganizationtowhichtheSIPelementissuingtherequestorresponsebelongs.
Organization:AltanaiTelecomCo.
Warningadditionalinformationaboutthestatusofaresponse.Listofwarn-code
300Incompatiblenetworkprotocol:301Incompatiblenetworkaddressformats:302Incompatibletransportprotocol:303Incompatiblebandwidthunits:304Mediatypenotavailable:305Incompatiblemediaformat:306Attributenotunderstood:307Sessiondescriptionparameternotunderstood:330Multicastnotavailable:331Unicastnotavailable:370Insufficientbandwidth:399Miscellaneouswarning:1xxand2xxhavebeentakenbyHTTP/1.1.
Warning:307isi.edu“Sessionparameter‘foo’notunderstood”Warning:301isi.edu“Incompatiblenetworkaddresstype‘E.164′”
AutheticationandAuthorizationrelatedheaders
Authentication-InfomutualauthenticationwithHTTPDigest.AUASMAYincludethisheaderfieldina2xxresponsetoarequestthatwassuccessfullyauthenticatedusingdigestbasedontheAuthorizationheaderfield.
Authentication-Info:nextnonce=”47364c23432d2e131a5fb210812c”
AuthorizationauthenticationcredentialsofaUA
Authorization:Digestusername=”Alice”,realm=”atlanta.com”,nonce=”84a4cc6f3082121f32b42a2187831a9e”,response=”7587245234b3434cc3412213e5f113a5432″
Proxy-Authenticatecontainsanauthenticationchallenge.
Proxy-Authenticate:Digestrealm=”atlanta.com”,domain=”sip:ss1.carrier.com”,qop=”auth”,nonce=”f84f1cec41e6cbe5aea9c8e88d359″,opaque=””,stale=FALSE,algorithm=MD5
Timers
exponentialback-offonre-transmissions
SessionExpireHeaderFeild
limitthetimeperiodoverwhichastatefulproxymustmaintainstateinformation.options
Useragentsmustteardownthecallaftertheexpirationofthetimer,orallercansendre-INVITEstorefreshthetimer,enablinga“keepalive”mechanismforSIP.
SDP(SessionDescriptionProtocol)
SIPcanbearmanykindsofMIMEattachments,onesuchisSDP.Itisastandardforprotocoldefinitionforexchangeofmedia,metadataandothertransportrealtedattributesbetweentheparticpantsbeforeestablishingaVoIPcall.
SDPsessiondescriptionisentirelytextualusingtheISO10646charactersetinUTF-8encodinganddescribedbyapplication/SDPmediatype.
ItshouldbenotedthatSDPitselfdoesnotincorporateatransportprotocolandcanbeusedwithdifferenceprotoclslikeSessionannouncementproctols(SAP),SIP,HTTP,ElectronicMAIlMIMEextension,RTSPetc.
IncaseofSIPSDPisencapsulatedinsideofSIPpacketanduseoffer/answermodeltoconveyinformationaboutmediastreaminmultimediasession.
SDPbodycontains2parts:sessionbasedsectionstartingwithv=lineandmediabsesctionstartingwithm=lineMediaandTransportInformationcancontaintypeofmedialikevideo,audio,transportprotocollikeRTP/UDP/IP,H.320andformatofthemediasuchasH.261video,MPEGvideo,etc.
SessionDescriptioninSDP
protocolversion(v=)protocolversionmostlyversion0
originatorandsessionidentifier(o=)
o=
o=-64768885762848743442INIP4127.0.0.1
sessionname(s=)andsessioninformation(i=)sessionnameistextualandcancontainemptyspaceorevens=-butmustnotbeempty.Sessioninfomrationisoptionaltextualinformationaboutthesession
URIofdescription(u=)
EmailAddressandPhoneNumber(“e=”and“p=”)
BothareoptionalfreetextstringSHOULDbeintheISO-10646charactersetwithUTF-8encoding
NothethatifgiventhePhonenumbersSHOULDfollowinternationalpublictelecommunicationnumberspecification(ITU-TRecommendationE.164)andbeprecededbya“+”.Spacesandhyphensmaybeusedtosplitupaphonefieldtoaidreadabilityifdesired.
[email protected]=+1617555-6011
ConnectionData(c=)connectioninformation—notrequiredifincludedinallmediainwhichmediaspecificconneciondataoverrideoverallsessionconnectiondata
c=
c=INIP4172.31.90.251
Ifthesessionismulticast,theconnectionaddresswillbeanIPmulticastgroupaddress.TTLshoudlbepresentinIPv4multicastaddress.IfconnectionisunicasttheaddresscontainstheunicastIPaddressoftheexpecteddatasourceordatarelayordatasink.
Bandwidth(b=)interpretedaskilobitspersecondbydefault
b=:
EncryptionKeys(k=)OnlyisSDPisexchangedinsecureandtrustedchannel,keysvabeexcahngedonthisSDPfield.Althoughthisprocessisnotrecomended,
k=clear:k=base64:k=uri:k=prompt
Attributes(a=)
extendstheSDPwithvalueslikeflags
a=inactive,a=sendonly,a=sendrecv,a=recvonly
MappingtheEncoderSpecfrom
a=rtpmap:/[/]
a=rtpmap:96opus/48000/2a=rtpmap:0PCMU/8000a=rtpmap:8PCMA/8000a=rtpmap:9G722/8000a=rtpmap:101telephone-event/48000a=rtpmap:97telephone-event/8000
ConferenecTypelike“broadcast”,“meeting”,“moderated”,“test”,
a=type:
Orientationportraitorlandscapeforwhiteboardsession
a=orient:
ICEcandidates
a=ice-pwd:86701d63e2d96ec42268679a
a=ice-ufrag:948a1316
a=rtcp-12133xr:rcvr-rtt=all:10000stat-summary=loss,dup,jitt,TTLvoip-metrics
Framepersecondforvideo
a=framerate:
Qualitybetween0–10(10beststillimage,5default,0wrst)
a=quality:
FormatspecificParameters
a=fmtp:
a=rtpmap:114AMR-WB/16000/1
a=fmtp:114mode-change-capability=2;max-red=220
a=rtpmap:113AMR-WB/16000/1
a=fmtp:113octet-align=1;mode-change-capability=2;max-red=220
a=rtpmap:102AMR/8000/1
a=fmtp:102mode-change-capability=2;max-red=220
a=rtpmap:115AMR/8000/1
a=fmtp:115octet-align=1;mode-change-capability=2;max-red=220
a=rtpmap:105telephone-event/16000
a=fmtp:1050-15
a=rtpmap:101telephone-event/8000
a=fmtp:1010-15
TimeDescriptioninSDP
Timing(t=)timethesessionisactive)
t=
Iftheissettozero,thenthesessionisnotbounded,thoughitwillnotbecomeactiveuntilafterthe.Iftheisalsozero,thesessionisregardedaspermanent.
t=00
RepeatTimes(r=)
zeroormorerepeattimesforschedulingasession
r=
timezoneadjustments(z=)
z=….
usefulforscejdulingsessionduringtransationtodaylightvsavingtostandardtimeandviceversa
MediaDescriptioninSDP
ForRTP,thedefaultisthatonlytheeven-numberedportsareusedfordatawiththecorrespondingone-higheroddportsusedfortheRTCPbelongingtotheRTPsession
m=…
m=audio20098RTP/AVP0101
willstreamRTPon20098andRTCPon20099
FormultipletransportportspairsofRTP,RTCPstreamarespecified
m=/…
m=audio20098/2RTP/AVP0101willstreamonepaironRTP20098,RTCP20099andRTP20100,RTCP20101
Ifnon-contiguousportsarerequired,theymustbesignalledusingaseparateattributelikeexample,“a=rtcp:”
AdditioanSDPfeatures:Inadditiontonormalunicastsessions,SDPcanalsoconverymulticastgroupaddressformediaonIPmulticastsession.Private(encryptionofSDP)orpublicsessionarenottreateddifferentlybySDPandtheyareentorelyafunctionofimplementingmechanismlikeSIPorSAP.OptiopnalSDPparamsincludeURI,Categorisation“a=cat:”,Internationalisationetc
Example1:TypicalAudiocallSIPINVITEshowingSIPheadersinblueandSDPingreenbelow
INVITEnbspsip:[email protected]/2.0
Via:SIP/2.0/UDPx.x.x.x:5060branch=z9hG4bK400fc6e6
From:"123456789"ltsip:[email protected]=as42e2ecf6
To:ltsip:[email protected]
Contact:ltsip:[email protected]
Call-ID:[email protected]
CSeq:102INVITE
User-Agent:nbspMatrixSwitch
Date:Thu,22Dec200518:38:28GMT
Allow:INVITE,ACK,CANCEL,OPTIONS,BYE,REFER
Content-Type:application/sdp
Content-Length:268
v=0
o=root1404014040INIP4x.x.x.x
s=session
c=INIP4x.x.x.x
t=00
m=audio26784RTP/AVP0818101
a=rtpmap:0PCMU/8000
a=rtpmap:8PCMA/8000
a=rtpmap:18G729/8000
a=rtpmap:101telephone-event/8000
a=fmtp:1010-16
a=fmtp:18nbspannexb=no----
c=*(connectioninformation-optionalifincludedatsession-level)
b=*(bandwidthinformation)
a=*(zeroormoremediaattributelines)
TheaboveSDPshows4supportedmediacodecsonaudiostreamwhichare0PCMU,8PCMA,18G729andfinally101usedfortelephoneevents.ItalsoshowsRTP/AVPasRTPprofileanddoesnotcontainanym=cideolinewhichshowsthatthisendpointdoesnotwantavideocall,onlyanaudioone.
Example2:VideoVallSIPinvitefromLinphone
SIPURIParams
InternetAssignedNumberAuthority(IANA)UniversalResourceIdentifier(URI)ParameterRegistrydefinesURIparamsthatcanbesuedalongwithSIPscheme
sip:user:password@host:port;uri-parameters?headers
compparam
signallingcompressionofSIPmessages
sip:[email protected];comp=sigcompVia:SIP/2.0/UDPserver1.foo.com:5060;branch=z9hG4bK87a7;comp=sigcomp
TheaobveexmapleindicatesthattherequesthastobecompressedusingSigComp
transport-param
SIPcanuseanynetworktransportprotocol.ParameternamesaredefinedforUDP(RFC768),TCP(RFC761),andSCTP(RFC2960).ForaSIPSURI,thetransportparameterMUSTindicateareliabletransport.
“transport=” (“udp” /“tcp” /“sctp” /“tls” /“ws”/other-transport)
sip:alice:[email protected];transport=tcp
maddrpaarm
Theserveraddress(detsiantionaddress,port,transport)tobecontactedforthisuser,overridinganyaddressderivedfromthehostfield.
Althoughdiscouraged,maddrURIparamhasbeenusedasasimpleformofloosesourcerouting.ItallowsaURItospecifyaproxythatmustbetraverseden-routetothedestination.
user-param
“user=” (“phone” “ip” “dialstring” other-user)
sip:1-212-555-1212:[email protected];user=phone
sip:123;[email protected];user=dialstring
method-param
“method=”Method
sip:atlanta.com;method=REGISTER?to=alice%40atlanta.com
annc-parameters(announcement)
ANNC-URLsip‑ind annc‑ind “@” hostport annc‑parameters uri‑parameters
sip:[email protected];\;play=file://fs.example.net//clips/my-intro.dvi;\;content-type=video/mpeg%3bencode%d3314M-25/625-50
sip-ind -“sip:” /“sips:”
annc-ind -“annc”
annc-parameters“;” play‑param[“;” delay‑param][“;” duration‑param][“;” repeat‑param][“;” locale‑param][“;” variable‑params][“;” extension‑params]
play-param–“play=” prompt‑url
prompt-url–“/provisioned/” announcement‑id
announcement-id =1*(ALPHA /DIGIT)
content-param“content‑type=” MIME‑type
VoiceXMLMediaServices
dialog-param“voicexml=” vxml-url; vxml-urlfollowstheURIsyntax
method-param–“method=” (“get” /“post”)
postbody-param-“postbody=” token
ccxml-param–“ccxml=” json‑value
aai-param-“aai=” json‑value
json-value–false /null /true /object /array /number /string
sip:[email protected];\voicexml=http://appserver.example.com/promptcollect.vxml;\maxage=3600;maxstale=0
dialog-params(promptandcollect)
DIALOG-URL =sip-ind dialog-ind “@” hostport dialog‑parameters
ttl-param(time-to-live)
ttlparameterdeterminesthetime-to-livevalueoftheUDPmulticastpacketandMUSTonlybeusedifmaddrisamulticastaddressandthetransportprotocolisUDP.
sip:[email protected];maddr=239.255.255.1;ttl=15
causeparam
“cause”EQUALStatus-Code;404Unknown/Notavailable;486Userbusy;408Noreply;302Unconditional;487Deflectionduringalerting;480Deflectionimmediateresponse;503Mobilesubscribernotreachable;380Servicenumbertranslation RFC8119–Section2
sip:[email protected];target=bob%40example.com;cause=486
SIPResponses
1xx—ProvisionalResponses
responsethattellstoitsrecipientthattheassociatedrequestwasreceivedbutresultoftheprocessingisnotknownyetwhichcouldbeiftheprocessinghasntfinishedimmediately.Thesendermuststopretransmittingtherequestuponreceptionofaprovisionalresponse.
100Trying180Ringing:Triigersalocalringingatcallersdevice181CallisBeingForwarded:UsedbeforetraneferingtoanotherUAsuchasduringforkingortranfertovoicemailServer
182Queued
183SessioninProgress:conveysinformation.HeadersfieldorSDPbodyhasmordetailsaboutthecall.UsedinannouncementsandIVR+DTMFtoobybeingfollowedby“Earlymedia”.
199EarlyDialogTerminated
2xx—SuccessfulResponses
finalresponsesexpressresultoftheprocessingoftheassociatedrequestandtheyterminatethetransactions.
200OK202Accepted204NoNotification
3xx—RedirectionResponses
Redirectionresponsegivesinformationabouttheuser’snewlocationoranalternativeservicethatthecallershouldtryforthecall.Usedforcaseswhentheservercantsatisfythecallandwantsthecallertotryelsewhere.Afterthisthecallerissupposetoresendtherequesttothenewlocation.
300MultipleChoices301MovedPermanently302MovedTemporarily305UseProxy380AlternativeService
4xx—ClientFailureResponses
negativefinalresponsesindicatingthattherequestcouldn’tbeprocessed duetocallersfault,forreasonssuchastcontainsbadsyntaxorcannotbefulfilledatthatserver.
400BadRequest401Unauthorized402PaymentRequired403Forbidden404NotFound405MethodNotAllowed406NotAcceptable407ProxyAuthenticationRequired408RequestTimeout409Conflict410Gone411LengthRequired412ConditionalRequestFailed413RequestEntityTooLarge414Request-URITooLong415UnsupportedMediaType416UnsupportedURIScheme417UnknownResource-Priority420BadExtension421ExtensionRequired422SessionIntervalTooSmall423IntervalTooBrief424BadLocationInformation428UseIdentityHeader429ProvideReferrerIdentity430FlowFailed433AnonymityDisallowed436BadIdentity-Info437UnsupportedCertificate438InvalidIdentityHeader439FirstHopLacksOutboundSupport470ConsentNeeded480TemporarilyUnavailable481Call/TransactionDoesNotExist482LoopDetected.483TooManyHops484AddressIncomplete485Ambiguous486BusyHere487RequestTerminated488NotAcceptableHere489BadEvent491RequestPending493Undecipherable494SecurityAgreementRequired
5xx—ServerFailureResponses
negativeresponsesbutindicatingthatfaultisatserver’ssideforcasessuchasservercantordoesntwanttorespondthetherequest.
500ServerInternalError501NotImplemented502BadGateway503ServiceUnavailable504ServerTime-out505VersionNotSupported513MessageTooLarge580PreconditionFailure
6xx—GlobalFailureResponses
requestcannotbefulfilledatanyserverwithdefinitiveinformation
600BusyEverywhere603Decline604DoesNotExistAnywhere606NotAcceptable
MandatorySIPheadersinSIPrespone
SIP/2.0200OK
Via:SIP/2.0/UDPhost.domain.com:5060
From:Bob
To:Altanai
Call-ID:[email protected]
CSeq:1INVITE
Via,From,To,Call-ID,and CSeq arecopiedexactlyfromrequest
SIPVoIPsystem Architecture
YoucanreadmoreaboutSIPbasedArchitecturehere:SIPbasedarchitecture
Re-INVITEandTarget-RefreshRequestHandling
AnINVITErequestsentwithinanexistingdialogisknownasare-INVITE.Are-Invitehasanoffer-answerexchangeandcanbeusedtodothefollowing
changethesessionand/ordialogparamschangetheporttowhichmediashouldbesent.changetheconnectionaddressormediatype.Hold/ReleaseandSUSPEND/RESUMErtpstreams(connectionaddressiszero).FAX(T.38andBypass).
Re-INVITEwithSDPuseCases
1.UASrejectsallchangesinparamsinre-INVITE
SitutaionwhereUACestablishesaudioonlycall
SDP1:m=audio30000RTP/AVP0
butlaterwantstoupgradetovideoaswellSDP:
m=audio30000RTP/AVP0
m=video30002RTP/AVP31
UASconfiguredtorejectvideostreams,canrejectthiswitha4XXerrorandgetACK.Nochangestosessionaremade
2.UASreceivesre-INVITEforparambutwantstoacceptfewandrejectothers,itsendsbackSDPwithacceptablechangeswith200OK
ForinstanceUACmovestohighbandwidthaccesspointandwantstoupdateIPofmediastream.Italsowansttoaddvideostream
initialSDP
m=audio30000RTP/AVP0c=INIP4192.0.2.1
newSDPinreINVITE
m=audio30000RTP/AVP0c=INIP4192.0.2.2m=video30002RTP/AVP31c=INIP4192.0.2.2
UASreturnsa200(OK)responsetoacceptIPbutsetstheportofthevideostreamtozeroinitsSDPtoshowrejectedofvideostream.
m=audio31000RTP/AVP0
c=INIP4192.0.2.5
m=video0RTP/AVP31
anotherexampleiswhenUACwwantstoaddanotheraudiocodecandalsoaddvideostreamtosession
orignalSDP
m=audio30000RTP/AVP0
c=INIP4192.0.2.1
re-inviteSDP
m=audio30000RTP/AVP03c=INIP4192.0.2.1m=video30002RTP/AVP31c=INIP4192.0.2.1
againtheUASwilloptionallyacceptthesomeparamcangeslikeaudiocodebutsetvideotonullIPaddress
m=audio31000RTP/AVP03
c=INIP4192.0.2.5
m=video31002RTP/AVP31
c=INIP40.0.0.0
3.UASreceivesre-INVITEbutwaitsforuserintervention
UASreceivesre-INVITEtoaddvideo,butinsteadofrejecting,itpromptsusertopermit.
SoUASprovidesanullIPaddressinsteadofsettingthestreamto‘inactive’becauseinactivestreamsstillneedtoexchangeRTPControlProtocol(RTCP)traffic
m=audio31000RTP/AVP0c=INIP4192.0.2.5m=video31002RTP/AVP31c=INIP40.0.0.0
Laterifuserrejectstheadditionofthevideostream.Consequently,theUASsendsanUPDATErequest(6)settingtheportofthevideostreamtozeroinitsoffer.
m=audio31000RTP/AVP0c=INIP4192.0.2.5m=video0RTP/AVP31c=INIP40.0.0.0
SipDetailed,Callflows,Architecturedescriptions,SIPservices,sipsecurity,sipprogrammingfromALTANAIBISHT
References:
RFC3261SIPRFC4566SDPhttps://tools.ietf.org/html/rfc4566RFC6141UpdatestheRFC3261withrespecttore-INVITEandUASbehaviourhttps://tools.ietf.org/html/rfc6141Techinvote:https://www.tech-invite.com/fo-abnf/tinv-fo-abnf-sipuriup.html
SIPVoIPsystemarchitecture basicsJuly13,2013In"SIP"SIP(SessionInitiationProtocol )July13,2013In"SIP"HostedIP-PBXand SBCMarch5,2019In"TelecomInfo"SessionBordercontrollerfor WebRTCAugust2,2016In"WebRTCSaaS"KamailioDNSand NATFebruary2,2019In"Kamailio"OpensipsJune6,2018In"Opensips"
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SpecializedinCPaaS,carrier-gradeWebRTC-SIPtelecomplatformsforUnifiedcommunication-collaboration,signalinggateways,SBC,softturrets,IoT-surveillanceandtelecomintegrations.
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TelecomR&DFaultToleranceandErrorCorrectioninWebRTCMarch10,2022FluctuatingNetworksDynamicBandwidthestimationJitterBufferDemandforHighQualityVideoTradeoffbetweenLatencyvsQualityBettercompressionalgorithmsvsCPUcomputeFullINTRA-frameRequest(FIR)PictureLossIndication(PLI)LayeringforadaptivestreamingRedundantEncoding(RED)inMediaPacketsCongestionFeedbackLoopReduceframequalityandr[…]AEC(EchoCancellation)andAGC(GainControl)inWebRTCMarch10,2022AcousticEchoHybrid/ElectronicEchoinPSTNphonesNoiseSuppressioninWebRTCEchoCancellationWebRTCEchoCancellationAutomaticGainControl(AGC)Echoisthesoundofyourownvoicereverberating.Iftheamplitudeofsuchasoundishighandintervalsexceed25ms,itbecomesdisruptivetotheconversation.Itstypescanbe…ContinuereadingAEC(Ec[…]VoIPAPIdesignDecember22,2021PublicAPIendpointsInternalAPIgatewaysAPIRateLimiterTokenbasedRateLimitingTokenbucketfilterHierarchicalTokenBucket(HTB)FairQueingCBQ(ClassBasedQueing)ModularQoScommand-Lineinterface(MQC)ShapingThrottlingVoIPmanagesCallsetupandteardownusingIPprotocol.TheAPIscanbeusedtoprovidepublicorinternalendpoinsttocreat[…]HighavailiabilityandScalibilityinVoIPplatformsDecember22,2021LoadBalancersMPLSService-discoveryKeepalive,unregisteringunhealthynodesReplicationDataStoreReplicationQuickResponse/LowlatencyScalabilityautoscallingPartitioiningMultiplePoPs(pointofpresence)MinimalLatencyandlowestamountoftarfficviapublicinternetHighavailiability(HA)59’sinaggregatefailuresHAforLoadbalancer(LB)H[…]EEP(formelyHEP)ExtensibleEncapsulationProtocolwithHOMERSeptember19,2021EEPduplicatesandIPdatagramandencapsulatesandsendsforremoterelatimemonitoringforSIPspecificalertsandnotifications.HEPispopularamongmanySIPserversincludingFreeswitch,Opensips,kamailio,RTPengineasanexternalmodule.intendedforpassiveduplicatedforremotecollectioncanbeusedforauditstorageandanalysisdoesnotalter[…]EnergyEfficientVoIPsystemsJuly19,2021DataCentresaretheconcentratedprocessingunitsfortheamazingInternetthatisdrivingthetechnologicalinnovationofourgenerationandhasbecomethebackboneofourglobaleconomy.DataCentresnotonlyprocess,storeandcarrytextualdataratheravastamountofcomputingisformultimediacontentwhichcouldrangefromsocialmedia…Continuerea[…]WhyLuaisagoodchoiceforScriptingcallconfigurationsinSIPserverslikeKamailioandFreeswitchDecember1,2020PrograminginSIPserversenablestheIPtelephonyprovidertoaddcomplexcontrolthatisdifficulttorealisewithsimpledialplanXMLandIVRmenus.ThesearebesthandledbyusingaprogramthatiscompiledwiththetelecomapplicationserverandinvokedbySIPrequestsorresponsesinthesession.Thismayincludeusing…ContinuereadingWhyLuaisag[…]TeleMedicineandWebRTCNovember24,2020Thesolutionenablesdoctors/nurses/medicalpractitionersandpatients todoHighdefinitionAudio/videocalls Endtoendencryptedp2pchats IntegrationwithHMS(hospitalmanagementsystem)tofetchhistoryofthepatients Screenssharingtoshowreportswithouttransferringthemasfiles IncludemoreconcernedpeopleofdoctorsusingMeshbasedpee[…]
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