Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subsequent Offers
Justin Uberti <juberti@google.com> Thu, 07 November 2013 07:11 UTC
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From: Justin Uberti <juberti@google.com>
Date: Wed, 06 Nov 2013 23:11:01 -0800
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To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subsequent Offers
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On Wed, Nov 6, 2013 at 10:40 PM, Paul Kyzivat <pkyzivat@alum.mit.edu> wrote: > On 11/6/13 6:48 PM, Harald Alvestrand wrote: > >> On 11/06/2013 11:06 PM, Martin Thomson wrote: >> >>> The question in the room was: >>> >>> Given a negotiated session with "A, B, and C", is an endpoint >>> permitted to create an offer that includes "D"? >>> >> >> That's not what I heard. >> >> What I heard was: >> >> X offers A, B and C (codecs being the canonical example). >> Y answers A (only). That means we have agreement to use A only. >> X wants to send a new offer. >> > > This is a subset of the possible cases. But lets stick with it for the > moment. > > > Three alternatives: >> >> 1) X MUST offer A, B and C >> 2) X MUST offer A (only) if no particular constraint is set, but MUST >> offer A, B and C if some (to-be-defined) constraint is set. >> 3) X MAY offer A, and MAY offer A, B and C (nondeterministic behaviour) >> >> I like option 2, for the reasons stated (deterministic, seems to do the >> job). >> > > SDP O/A recommends an offer that contains A, but allows offering B and C > (or D) without A. Of course that could cause a great deal of pain, but > maybe X has no choice due to some change of situation. > > If JSEP wants to restrict to (2) then I don't see that as a problem. (But > be prepared for the possibility of *receiving* an offer that doesn't > contain A.) But I think it also ought to be possible for the non-default > offer to contain A plus anything else. > > A more complex case is: > X offers A, B, C > Y answers A, B > > Then X begins using A, and not using B. > When doing next offer, > 1) X MUST offer A, B, C > 2) X MUST offer A, B > 3) X MUST offer A > 4..N) X MUST offer one of above by default, but may offer more according > to some constraint. > > X may be using A in this case, but Y may be using B, so #3 would be bad IMO. (Remember, the reason for the new offer is because some other property of the session changed.) #2 would be the default behavior, and #1 would be the optional behavior that the application could choose. > (Note that audio easily can result in negotiating two codecs, where one of > them is telephone-events.) > > Thanks, > Paul > > > A great many people said yes, because that is how SDP is most commonly >>> used. >>> >>> I agree that not offering A, B or C would be bad. >>> >>> On 6 November 2013 14:01, Hutton, Andrew <andrew.hutton@unify.com> >>> wrote: >>> >>>> I vote for option 2 – Application controls renegotiation through >>>> constraint. >>>> >>>> >>>> >>>> Option 1 would be bad. >>>> >>>> >>>> >>>> Option 3 would be very bad. >>>> >>>> >>>> >>>> Andy >>>> >>>> >>>> >>>> >>>> >>>> From: rtcweb-bounces@ietf.org [mailto:rtcweb-bounces@ietf.org] On >>>> Behalf Of >>>> Justin Uberti >>>> Sent: 06 November 2013 13:37 >>>> To: Michael Procter >>>> >>>> >>>> Cc: rtcweb@ietf.org >>>> Subject: Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subsequent Offers >>>> >>>> >>>> >>>> From the room discussion, I sensed 3 possible options to move forward. >>>> >>>> 1) MUST NOT renegotiate codecs etc. (new PeerConnection if you want to >>>> renegotiate) >>>> >>>> 2) MUST NOT renegotiate codecs etc. by default, but MUST support option >>>> to >>>> renegotiate (application controls renegotiation through constraint) >>>> >>>> 3) SHOULD NOT renegotiate codecs etc, but implementation MAY do so if >>>> desired (no application logic needed, but non-deterministic API >>>> behavior) >>>> >>>> >>>> >>>> "etc" here would not include anything that would result in the offer >>>> changing from the previously agreed-upon local description, including >>>> codecs, RTP header extensions, RTCP feedback mechanisms, BUNDLE >>>> groupings, >>>> or use of FEC/RTX. >>>> >>>> >>>> >>>> I proposed #1 in the room, but see #2 as a reasonable solution. That >>>> provides the application with full control over what it wants, as well >>>> as >>>> deterministic behavior. >>>> >>>> >>>> >>>> On Wed, Nov 6, 2013 at 1:29 PM, Justin Uberti <juberti@google.com> >>>> wrote: >>>> >>>> Yes, it would. But I think the problem still exists for applications >>>> that >>>> don't use partial offer/answers. >>>> >>>> >>>> >>>> On Wed, Nov 6, 2013 at 12:47 PM, Michael Procter <michael@voip.co.uk> >>>> wrote: >>>> >>>> On 3 November 2013 22:55, Justin Uberti <juberti@google.com> wrote: >>>> >>>>> According to section 5.2.5, it seems that this is only the cases for >>>>> offers >>>>> triggered by offerless reINVITEs. I don't think we want to be >>>>> re-allocating >>>>> and negotiating codecs every time we want to make a change to the >>>>> session >>>>> descriptions in use. >>>>> >>>> Would the partial offer/answer work address at least part of this? >>>> m-lines that you don't want to change wouldn't need to be advertised >>>> at all, rather than being advertised with a restricted codec set. >>>> >>>> Michael >>>> >>>> >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> rtcweb mailing list >>>> rtcweb@ietf.org >>>> https://www.ietf.org/mailman/listinfo/rtcweb >>>> >>>> _______________________________________________ >>> rtcweb mailing list >>> rtcweb@ietf.org >>> https://www.ietf.org/mailman/listinfo/rtcweb >>> >> >> >> > _______________________________________________ > rtcweb mailing list > rtcweb@ietf.org > https://www.ietf.org/mailman/listinfo/rtcweb >
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Paul Kyzivat
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Parthasarathi R
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Justin Uberti
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Hutton, Andrew
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Michael Procter
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Justin Uberti
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Justin Uberti
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Hutton, Andrew
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Martin Thomson
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Hutton, Andrew
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Harald Alvestrand
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Martin Thomson
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Paul Kyzivat
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Justin Uberti
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Martin Thomson
- Re: [rtcweb] draft-ietf-rtcweb-jsep-05 - Subseque… Stefan Håkansson LK