RE: [Sip] SIPit 21 : Topics that attendees argued about

I am surprised that this caused any confusion. RFC 3264 seems pretty
clear to me.

Citing from section 6.1:
  "The answerer MUST send using a media format in the offer
   that is also listed in the answer, and SHOULD send using the most
   preferred media format in the offer that is also listed in the
answer."

and from section 7:
  "The offerer MAY immediately cease listening for media formats that
   were listed in the initial offer, but not present in the answer."

So, why should the offerer be expected to deal with formats not present
in the answer? (Of course, the offerer must be prepared to receive ALL
offered formats BEFORE the answer arrives)

Regards,
Ernst Horvath

> -----Original Message-----
> From: Christer Holmberg [mailto:christer.holmberg@ericsson.com] 
> Sent: Thursday, November 22, 2007 11:34 AM
> To: ravishankar.shiroor@wipro.com; rjsparks@nostrum.com; sip@ietf.org
> Subject: RE: [Sip] SIPit 21 : Topics that attendees argued about
> 
> 
> Hi,
> 
> I agree with Ravi. 
> 
> Eventhough you in theory is supposed to be able to receive what you
> offer - no matter what you get in the answer - I think that 
> in real life
> the only codecs that participants will be prepared to send/receive are
> the ones sent both in the offer and the answer. That is also 
> the reason
> why the answer normally doesn't contain additional codecs - it mostly
> contains a subset of the codecs in the offer.
> 
> Regards,
> 
> Christer
> 
> 
> 
> >I was surprised to find 
> > 
> >>* There were implementations that offered an m-line with 
> codecs A, B, 
> >>and C, got an answer with C, then got upset when they got 
> RTP with A 
> >>(which is quite legal).
> > 
> >On the list (like others who argued about it I think).
> > 
> >I had some offline discussions with some of the members on this.
> >While I agree this seems legal, this seems very 
> >counter-intuitive and may result in wasted resources, would it not?
> > 
> >For example, if the offerer is a conference bridge or a 
> >transcoder, and has a limited number of codecs of each type 
> >he offers, why should it hold on to one codec of each type 
> >for the duration of the session, even though the answerer has 
> >not supported it?
> > 
> >Any particular reason why this should be continued as a legal 
> >scenario?
> >Would it not be possible change it to say that the Offerer 
> >needs to expect only those codecs which answerer has 
> >explicitly supported in the answer?
> > 
> >Regards,
> >Ravi.
> > 
> > --
> >  
> > Ravishankar. G. Shiroor
> > Wipro Technologies, Bangalore.
> >  
> > ravishankar.shiroor@wipro.com
> > --
> > 
> > > -----Original Message-----
> > > From: Robert Sparks [mailto:rjsparks@nostrum.com]
> > > Sent: Tuesday, November 20, 2007 2:38 AM
> > > To: sip List
> > > Subject: [Sip] SIPit 21 : Topics that attendees argued about
> > > 
> > > Digging through my notes:
> > > 
> > > Here are some of the topics where people were arguing. I'm 
> > capturing 
> > > the smaller topics here. Larger arguments will get their 
> > own message.
> > > 
> > > * There were arguments about the dynamic payload map from 
> > numbers to 
> > > codecs (identified in the SDP and sent in the RTP) being 
> > the same in 
> > > the offer and the answer . The spec says they SHOULD. Some 
> > > implementations were insisting they MUST.
> > > * There were arguments around preserving the relative order 
> > of codecs 
> > > on an m-line between the offer and the answer. The specs 
> say SHOULD.
> > > * There were implementations that offered an m-line with 
> > codecs A, B, 
> > > and C, got an answer with C, then got upset when they got 
> > RTP with A 
> > > (which is quite legal).
> > > * There were arguments about deleting rejected m-lines on 
> > re-invites 
> > > (which you cannot do), and on reusing the slot they occupy in re- 
> > > invites (which you can do).
> > > * There were implementations that didn't add the 
> refresher tag in a 
> > > session-refresh message when they were the refresher and 
> there were 
> > > arguments about whether that meant the other side could 
> > take the role.
> > > * Several implementations handled a=sendonly as a session 
> > attribute, 
> > > but not a media attribute - it can appear in either place.
> > > 
> > > 
> > > 
> > > _______________________________________________
> > > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > > This list is for NEW development of the core SIP Protocol Use 
> > > sip-implementors@cs.columbia.edu for questions on current sip Use 
> > > sipping@ietf.org for new developments on the application of sip
> > 
> > 
> > _______________________________________________
> > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > This list is for NEW development of the core SIP Protocol Use 
> > sip-implementors@cs.columbia.edu for questions on current sip 
> > Use sipping@ietf.org for new developments on the application of sip
> > 
> 
> 
> _______________________________________________
> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> This list is for NEW development of the core SIP Protocol
> Use sip-implementors@cs.columbia.edu for questions on current sip
> Use sipping@ietf.org for new developments on the application of sip
> 

_______________________________________________
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This list is for NEW development of the core SIP Protocol
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Use sipping@ietf.org for new developments on the application of sip