Re: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line for bundled session

Christer Holmberg <> Sun, 23 September 2012 20:37 UTC

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From: Christer Holmberg <>
To: Parthasarathi R <>, 'Lishitao' <>, "'Ejzak, Richard P (Richard)'" <>, "" <>
Date: Sun, 23 Sep 2012 22:37:13 +0200
Thread-Topic: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line for bundled session
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Subject: Re: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line for bundled session
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>IIUC, The same port offer may be rejected by answerer irrespective of
>"m=bundle" or "a=group:BUNDLE" as it is not just new SDP syntax
>but also, the same port offer may have impact in other layers like RTP
>in answerer side implementation. The bundling of the different media
>in the same port is not guaranteed to negotiate in the answer side with
>"m=bundle" mechanism. The point is that answerer will reject in case the
>same port offer is not accepted in the specific implementation.

If the m=bundle proposal, you don't have to use the same ports. You can assign a separate port for the m=bundle media description.

>Apart from this, The individual attribute behavior for bundle has to be
>defined somewhere irrespective of "m=bundle" or "a=group:BUNDLE". Say ptime
>attribute applies for the audio codecs only or applies for video codecs
>as well in the bundle has to be defined. I'm not see much advantage with
>"m=bundle" here.

It is already possible to specify attribute values for individual SSRCs. We could do something similar for media types if we want.

>Instead, Let us discuss the generic categories of attributes and mention in this draft.

I am not sure I understood.

For sure we will have to discuss how/if attributes are affected, but we need to have a general idea on how the multiplexing is going to be offered. Same ports, m=bundle, or something else...

So, again, if you have any ideas on how to do it I'd like to hear them :)



-----Original Message-----
From: Christer Holmberg []
Sent: Friday, September 21, 2012 10:57 PM
To: Parthasarathi R; 'Lishitao'; 'Ejzak, Richard P (Richard)';
Subject: RE: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line
for bundled session


>I agree with Cullen & others that m=bundle does not have consensus. We need
>more discussion and analysis. The current Bundle syntax is designed in a
>to reuse lot of existing SDP mechanism (Syntax & Semantics). If possible,
>let us try to fix the open issue with the current mechanism before
>with m=bundle approach.

Feel free to provide input on how you think we can solve that issue :)



-----Original Message-----
From: [] On Behalf Of
Sent: Friday, September 21, 2012 7:21 AM
To: Christer Holmberg; Ejzak, Richard P (Richard);
Subject: Re: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line
for bundled session

> -----Original Message-----
> From: [] On Behalf
> Of Christer Holmberg
> Sent: Friday, September 21, 2012 3:32 AM
> To: Ejzak, Richard P (Richard);
> Subject: Re: [MMUSIC] Possible BUNDLE alternative syntax: explicit m-line
> bundled session
> Hi,
> >>> m=bundle requires significant extensions to the syntax and also a near
> >>> doubling in the size of the SDP.  It is harder to specify allowed
> >>> combinations of codecs and other options that are normally associated
> >>> with a single m line.
> >>
> >> Please give an example.
> >
> > To specify two types of audio flows with very different characteristics
I would
> normally have separate media lines with separate codec lists and
> One may require DTMF and the other silence suppression in addition to the
> selected (but different)
> > codecs.  We need to keep this characteristic.  We also need a way of
> specifying bandwidth per (old) media line, which is already supported
> separate media lines but requires that something new be defined for
> What about RTCP
> > characteristics?  We certainly want to specify them per (old) media
> >
> > I understand that this can be done with m=bundle, but it requires new
> Why bother if we have something that can work?
> I am not sure it requires new syntax, if you e.g. can use the ssrc
attribute in
> order to map attributes to specific flows.

I would suggest that put the m=bundle proposal in a separate new personal
draft or in the annex of the existing working draft, and
make a comparison for this proposal and the existing proposal. That will
make it more clear.
For the existing proposal, I believe that people are not totally against,
although it has some issues. (the m=bundle proposal also has some issues).


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