Re: [MMUSIC] Proposal for what bundle should say about demux

Emil Ivov <emcho@jitsi.org> Fri, 24 May 2013 14:40 UTC

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Date: Fri, 24 May 2013 17:40:25 +0300
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From: Emil Ivov <emcho@jitsi.org>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [MMUSIC] Proposal for what bundle should say about demux
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On May 24, 2013 5:16 PM, "Paul Kyzivat" <pkyzivat@alum.mit.edu> wrote:
>
> On 5/24/13 5:14 AM, Emil Ivov wrote:
>>
>> On 24.05.13, 12:02, Kevin Dempsey wrote:
>>>
>>> I didn't say anything about changing the PTs.
>>
>>
>> Sorry, I misunderstood.
>>
>>> The answerer decides what
>>> it codecs it will use from the ones listed in the offer. If it doesn't
>>> support any other mechanism to allow demux then it must choose codecs
>>> that have PTs on only one m-line, or not accept the BUNDLE.
>>
>>
>> Matching packets to m= lines is the concern of the receiving party. So
>> is the mechanism that it uses. What you are suggesting is for the
>> answerer to basically say: "It seems to me that you won't be able to
>> demux these two payloads so I will not send them to you because I know
>> better".
>>
>> In the same time the offerer may be planning on using a demux technique
>> that the answerer simply isn't aware of. For example (and this is really
>> just to make a point, so please don't assume I am suggesting something
>> like this in general) if 101 is mapped to both telephone-event and VP8,
>> demuxing can be easily made without any other knowledge of SSRC or
>> header extensions.
>
>
> ISTM that after the O/A exchange both sides need to have a common
> understanding that their communications will be understandable.

I assume this means you agree that an offerer has to make sure at least one
of the demuxing mechanisms it supports will be understood by the answerer.

Emil

--sent from my mobile
>
> If the combination of the offer and answer aren't sufficient for each
side to encode what it sends in a way that it knows can be demuxed
according in accord with the O/A, then that offer should be incorrect.
>
> IMO injecting "magic" into this isn't helpful.
>
>         Thanks,
>         Paul
>
>
>> Cheers,
>> Emil
>>
>>
>>>
>>>
>>> On 24 May 2013 09:59, Emil Ivov <emcho@jitsi.org
>>> <mailto:emcho@jitsi.org>> wrote:
>>>
>>>      On 24.05.13, 11:40, Kevin Dempsey wrote:
>>>      > Isn't the onus on the answerer to ensure the demux is possible,
>>>      since it
>>>      > is accepting the bundle. Therefore if it doesn't support
signalling
>>>      > SSRCs or an offerred 'fancy-RFC m-line matching' method, it must
only
>>>      > send PTs that are tied to a single m-line.
>>>
>>>      PTs are defined by the offerer. The answerer cannot change them
for the
>>>      offerer-bound direction (even if it could request different values
for
>>>      the packets that it, the answerer, is going to receive).
>>>
>>>      Emil
>>>
>>>
>>>      >
>>>      >
>>>      > On 24 May 2013 08:17, Emil Ivov <emcho@jitsi.org
>>>      <mailto:emcho@jitsi.org>
>>>      > <mailto:emcho@jitsi.org <mailto:emcho@jitsi.org>>> wrote:
>>>      >
>>>      >     On 24.05.13, 00:59, Paul Kyzivat wrote:
>>>      >     > IMO the "before the O/A completes" issues are separate from
>>>      the "after
>>>      >     > the O/A completes" issues. I'm still not convinced that the
>>>      >     "before the
>>>      >     > O/A completes" issues are important. (We have reliable 183
>>>      >     responses to
>>>      >     > deal with it.) But I'm ok with Cullen using PT to solve
that
>>>      >     problem if
>>>      >     > he thinks he needs to.
>>>      >
>>>      >     I wasn't referring to "before the O/A completes" situations.
>>>      If your
>>>      >     peer does not support fancy-RFC m-line matching nor does it
>>>      provide
>>>      >     SSRCs, you have to be able to fall back to PT demuxing.
>>>      >
>>>      >     Therefore, all your offers have to accommodate for that
>>>      possibility
>>>      >     unless you know that the offer is going to someone who also
>>>      supports
>>>      >     other mechanisms.
>>>      >
>>>      >     Emil
>>>      >
>>>      >     --
>>>      >     https://jitsi.org
>>>      >     _______________________________________________
>>>      >     mmusic mailing list
>>>      >     mmusic@ietf.org <mailto:mmusic@ietf.org>
>>>      <mailto:mmusic@ietf.org <mailto:mmusic@ietf.org>>
>>>      >     https://www.ietf.org/mailman/listinfo/mmusic
>>>      >
>>>      >
>>>
>>>      --
>>>      https://jitsi.org
>>>
>>>
>>
>