Re: [MMUSIC] UP: Can a partial offer be a full offer?

Christer Holmberg <> Fri, 16 August 2013 07:35 UTC

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From: Christer Holmberg <>
To: "Cullen Jennings (fluffy)" <>
Thread-Topic: [MMUSIC] UP: Can a partial offer be a full offer?
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Date: Fri, 16 Aug 2013 07:35:03 +0000
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Subject: Re: [MMUSIC] UP: Can a partial offer be a full offer?
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It is ok to only send m- line(s) that are changed.

But, again, when you in a POF/PAN change on m- line explicitly, other m- lines may be changed implicitly. So, if you at the same time explicitly (using a separate POF/PAN) also try to change those other m- line, there will be a collision.

Or, as Paul says, if multiple simultaneous POF/PANs change session level information, there will be collision.

MAYBE we could restrict usage of POF/PANs, and say that they MUST NOT be used to change session level information...



-----Alkuperäinen viesti-----
Lähettäjä: Cullen Jennings (fluffy) [] 
Lähetetty: 14. elokuuta 2013 1:54
Vastaanottaja: Christer Holmberg
Kopio: Hadriel Kaplan; mmusic
Aihe: Re: [MMUSIC] UP: Can a partial offer be a full offer?

You only want to send the m blocks that have changed because if you send other ones, you up the chances of both sides sending the same m block at the same time and being back into the glare problem. 

It seems to me the options are either 1 or 2 would make sense 

1)  the sender SHOULD only send m m blocks with a change (which might be all of them) and receiver MUST be prepared to receive any number. 

2) you can only send one m block in  a partial Off or Ans - but you can have several outstanding at a time

On Aug 5, 2013, at 10:35 AM, Christer Holmberg <> wrote:

> Hi,
> I see no issue with multiple m- lines - just wanted to verify that it would be allowed :)
> Regards,
> Christer
> Sent from Windows using TouchDown (
> -----Original Message-----
> From: Hadriel Kaplan []
> To: Christer Holmberg []
> CC: mmusic []
> Subject: Re: [MMUSIC] UP: Can a partial offer be a full offer?
> On Aug 5, 2013, at 11:17 AM, Christer Holmberg <> wrote:
> > Note that my re-INVITE/UPDATE example is based on the assumption that one can use partial offers/answers with SIP, on the wire. Not sure if that was part of the agreed scope for the UP.
> Definitely NOT agreed on.  Doesn't mean it won't happen in the future, but the scope of UP was limited to WebRTC for now.  We can debate which parts of UP are generically applicable, and which not.  For SIP, this isn't the right WG for that debate.
> > But, even without that, I think the question on including all m- lines on a partial offer still applies :)
> I don't see why WebRTC would restrict itself in any way regarding the number of m-lines in a partial offer/answer.  Nothing "breaks" if all m-lines are in it, does it?  The real question is if it can be greater than *one* m-line.  If it can, and I think it can, then I can't see how the exact quantity of them matters.  The only downside is you increase the chance of glare, I assume.
> Afaik, the 'mid' attribute is there to identity which m-lines in the partial offer correspond to which m-lines in the full ordered set. (the 'mid' could have even been an index number, except it's also used to avoid glare when adding m-lines, which a numeric index wouldn't have done)  So what's the issue with one or multiple m-lines?
> -hadriel
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