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Re: [MMUSIC] Unified Plan for SDP Handling - multiple media sources

"Roni Even" <ron.even.tlv@gmail.com> Fri, 19 July 2013 06:15 UTC

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From: Roni Even <ron.even.tlv@gmail.com>
To: 'Martin Thomson' <martin.thomson@gmail.com>, 'Adam Roach' <adam@nostrum.com>
References: <00ad01ce826e$43666300$ca332900$@gmail.com> <CABkgnnVWL71QPOjqxXJCEr1NK93JOwpmY_CgiObpcUdfaDk2jA@mail.gmail.com> <AE206958-4085-4B6C-A747-D4D60C5CD7FE@vidyo.com> <51E61C99.8040305@nostrum.com> <A0791C6A-9F74-4FA6-BD6B-FCBAF9A5E966@vidyo.com> <51E71052.7010206@nostrum.com> <CABkgnnVVFxYtMcn06iS1J7_4PaLsEXwCcy-OWG6CmWsFXRsNKg@mail.gmail.com>
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Date: Fri, 19 Jul 2013 09:13:48 +0300
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Cc: 'Jonathan Lennox' <jonathan@vidyo.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] Unified Plan for SDP Handling - multiple media sources
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> -----Original Message-----
> From: mmusic-bounces@ietf.org [mailto:mmusic-bounces@ietf.org] On
> Behalf Of Martin Thomson
> Sent: 18 July, 2013 5:21 AM
> To: Adam Roach
> Cc: Jonathan Lennox; mmusic@ietf.org
> Subject: Re: [MMUSIC] Unified Plan for SDP Handling - multiple media
> sources
> 
> On 17 July 2013 14:44, Adam Roach <adam@nostrum.com> wrote:
> > On 7/17/13 16:40, Jonathan Lennox wrote:
> >>
> >> That said, what I still don't see is, if you have the correlator, why
> >> you then actually need to send the a=ssrc in the SDP at all? The
> >> correlator should be sufficient for disambiguation, and it lets the
> >> sender switch the ssrc it's sending for an m-line without needing a
fresh
> offer/answer.
> >
> >
> > That might be worth exploring. I honestly haven't given it a whole lot
> > of thought. Perhaps Justin or Martin have a more well-formed opinion
> > on the topic?
> 
> I did consider this, but there are several reasons that I prefer to have
> signaling.  The main one being that it is the only guaranteed way to get
this
> information through.  In the happy cases, the RTP header is enough, but if
> you are losing packets at session startup (a real possibility in some
> configurations), or RTP header extensions are being dropped, or you need
to
> communicate about an in progress stream and can't guarantee that you can
> cause the sender to re-send a few packets with the header extension, or
...
> 
> Basically, there are too many ways for the RTP extension to break.
> Not enough that it isn't hugely valuable for dealing with the race, but it
can't
> be the only mechanism that you rely on.
[Roni Even]  One of the reasons we have also SDES message with the ID is
because the header extension is optional and can be removed on the path. 


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