Paulo, The offer/answer model in SIP mandates that the answer be received reliably. This is achieved either using reliable provisional responses, or by putting it in the 2xx response. The callee UA MAY also add SDP to any 1xx provisional responses it sends (section 13.2.1 second bullet), but then the SDP in the 2xx MUST be the same.
As per RFC3261, the first answer received (be it in the 1xx response or in the 2xx) is used The benefit of putting the SDP in the 180 response is that the caller may receive this answer earlier than the one in the 2xx (but: not guaranteed). If the 1xx arrives, the caller can start setting up media streams, codecs, sockets etc, which results in a (slightly) faster call setup Regards, jeroen ----- Original Message ----- From: "Paulo de Arruda Borelli" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Cc: <[EMAIL PROTECTED]>; <[email protected]> Sent: Wednesday, January 25, 2006 9:59 AM Subject: Re: [Sip-implementors] 180 Ringing with SDP > Hi Amar, > > I can't understand why are you talking about reliable responses... They > are > not necessarily related to the SDP usage. I can't find anything, on the > RFC > excerpts you selected, telling that SDP is ok in 180 responses. > > Would you clarify this why you selected these excerpts? > > Thank you > Paulo. > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] > Sent: Wednesday, January 25, 2006 2:46 AM > To: Paulo de Arruda Borelli > Cc: [email protected]; > [EMAIL PROTECTED] > Subject: Re: [Sip-implementors] 180 Ringing with SDP > > Hi, > > As per the RFC 3262 any response between 101 to 199 can be sent reliably. > > From sec 3. > "A UAS MUST NOT attempt to send a 100 (Trying) response reliably. > Only provisional responses numbered 101 to 199 may be sent reliably. > If the request did not include either a Supported or Require header > field indicating this feature, the UAS MUST NOT send the provisional > response reliably." > > From sec 4. > "If a provisional response is received for an initial request, and > that response contains a Require header field containing the option > tag 100rel, the response is to be sent reliably. If the response is > a 100 (Trying) (as opposed to 101 to 199), this option tag MUST be > ignored, and the procedures below MUST NOT be used." > > So there is no harm in sending SDP in 180 ringing for early media. You > should not restrict it only to 183. > > > Rgds, > Amar > The greatest enemy of best is "good." If you're willing to accept "good" > you'll never be the "Best." > > > > "Paulo de Arruda > Borelli" > <[EMAIL PROTECTED] To > om.br> <[email protected]> > Sent by: cc > sip-implementors- > [EMAIL PROTECTED] Subject > ia.edu [Sip-implementors] 180 Ringing with > SDP > > 01/25/2006 06:18 > AM > > > > > > > > Hi, > > > > Why would an UAC send 180 Ringing with SDP? If it's supposed to use early > media, then 183 Session Progress is more appropriate, right? > > > > In my understanding, 180 with SDP is contradictory. 180 means: "play a > local > ringback tone". But the SDP content means: open the media path (in my > scenario, the original INVITE message did include SDP too). > > > > So what is the reason for using 180 with SDP in the scenario bellow? > > INVITE/SDP from A to B > > 180/SDP from B to A > > 200/SDP from B to A > > > > Thank you, > > > > Paulo A. Borelli > Gerente de Engenharia / Engineering Manager > TMais S.A. > VoIPMais: +55-11-2626-1080, r. 1136 > Cell: +55-11-9282-5990 > <BLOCKED::mailto:[EMAIL PROTECTED]> [EMAIL PROTECTED] > <BLOCKED::http://www.tmais.com.br> www.tmais.com.br > > > > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors > > > > *********************** FSS-Unclassified *********************** > > > _______________________________________________ > Sip-implementors mailing list > [email protected] > https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
