Jonathan Rosenberg wrote:
>
> >>4. Declare that simcap is overkill for this one problem, and define a
> >>single attribute, a=pickone, which says to choose only one of the
> >>codecs in the m line.
> >>The "I can do one of N, but only one at a time" problem, IMHO, the
> >>only
> >>capability problem that anyone actually has in real usage. I will note
> >>that, in fact, this is the only capabilities question ever asked on
> >>sip-implementors.
> >>
> >>A single attribute would easily solve it. If you want to do rfc2833
> >>along with any one of N other codecs, you could use fid along with
> >>this, to include an m line with the rfc2833, and then another m line with
> >>the N codecs and the a=pickone attribute.
> >>
> >>
> >
> > However that would require use of multiple ports which could lead to
> > multiple
> > resource reservations.
>
> Why? The rfc2833 could be on the same port, no?
>
No. The fid-draft does not allow the different "m=" lines to have the same
destination (IP address and port)
>
> > - if fid is included in the offer, but not supported by the answerer,
> > the handling
> > may not be all that graceful.
>
> Right.
>
> I am not wed to this specific mechanism. However, from my
> hopefully-now-correct understanding of simcap, it seems that it simply
> doesn't help at all with this issue of doing only one codec at a time.
It doesn't solve this particular problem by itself, however it provides a
mechanism that can be used to help solve it while remaining backwards
compatible. In its present form, you can send an INVITE/offer listing only one
codec in the "m=" line, and then include all codecs supported in the
capabilites. The answerer can accept this, and then do another re-INVITE
picking one or more codecs from the capabilites if you wants to use a different
one.
>
> So, options 1 and 2 above are no-go.
>
> Another possibility is to add an extension to simcap which allows you to
> convey this one particular constraint.
>
Right. In that case you would probably also define an offer/answer extension
that would the answerer to pick codecs from the capabilities, and not just the
"m=" line.
-- Flemming
--
Flemming Andreasen
Cisco Systems
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