Re: [MMUSIC] What is an m-line?

Emil Ivov <> Thu, 16 May 2013 19:03 UTC

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Date: Thu, 16 May 2013 22:03:08 +0300
From: Emil Ivov <>
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To: Martin Thomson <>
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Subject: Re: [MMUSIC] What is an m-line?
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On 16.05.13, 21:01, Martin Thomson wrote:
> On 16 May 2013 10:52, Emil Ivov <> wrote:
>> Could you please be more specific about the sorts of problems you
>> expect and how they are caused by adhering to the basics of RTP?
> I'm not a strong proponent of these things, and I expect those
> proponents to stand up and say something.  However, it is my
> understanding that in a call transfer case, the arrival of a new SSRC
> is treated as though the remote source has been switched out, not as
> though a new participant has been added to the session. 

Correct, however this happens after prior signalling which pretty much
destroys the existing RTP session.

> The same has
> to be true when a new SSRC is chosen in the case of a collision.

Indeed and it seems to me the above also applies here since sources that
choose a new identifier would first end their existing session with a BYE.

> This is clearer when you talk about video.  Does the video from the
> new SSRC go in the same window (/frame/<video> tag) as the existing
> SSRC, or does it go in a new window?

Given that in both cases we have one session ending and another
commencing, I'd say that the natural way to handle this would be to have
one video component removed and another added.