I think that the main advantage of the address field in the origin is that it helps to ensure that the 'o-line' is unique. This helps when checking SDP renegotiations to determine if there are changes or not, especially when working through a B2BUA. RFC3264 describes this checking in more detail.
Regards, Michael > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:sip-implementors- > [EMAIL PROTECTED] On Behalf Of Attila Sipos > Sent: 14 December 2006 13:40 > To: Gary Cote; sip-implementors > Subject: Re: [Sip-implementors] Significance of address in the SDP > originline > > > Hi Gary, > > (since no-one else has replied...) > > I don't know but isn't the origin the "controller" of the SDP? > So, if you've got some kind of 3rd party thing which is controlling > the content of the SDP, then that'd be shown in the o= line. > Whereas the c= line (obviously) just tells you where to send the media. > > I would agree that it doesn't seem to have any specified > active role (so far) but seems to be there for informational > purposes only. > > I also agree that it doesn't seem to have any role in offer/answer. > > So, that's my opinion. > > Regards, > Attila > > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Gary Cote > Sent: 13 December 2006 17:18 > To: sip-implementors > Subject: [Sip-implementors] Significance of address in the SDP origin > line > > > Short version: does the address field in the origin line have any > particular significance > in SIP? I'm thinking no, but would appreciate a second opinion. > > Long version: > > Here's an snippet from a 183 response with SDP answer that I captured: > > Contact: <sip:[EMAIL PROTECTED]:10000> > o=Sonus_UAC 7952 20059 IN IP4 69.59.245.131 > c=IN IP4 69.59.245.132 > > I was explaining to someone what the various addresses in a SIP message > mean. > For example, one could say that the address in the Contact header > specifies where the > UA wants to receive SIP messages; and the address in the c= line is where > it wants to receive RTP/RTCP packets. > > Note that the origin address is different from either of these. I > couldn't think of any > particular use for that address field. And after searching the various > specs and mailing > lists, I still can't come up with one. > > So ... I've tentatively concluded that the address has no particular > relevance to SIP > call setup or the offer/answer exchange (other than the fact that all > of the fields in the > origin line are used to identify a unique SDP). > > Would anyone care to comment on that? > > -- > Gary Cote > www.awardsolutions.com > _______________________________________________ > 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 _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
