Re: [MMUSIC] WGLC on draft-ietf-mmusic-rfc4756bis-03

Dear Ali,

I am not sure if the SDP signaling is covering all cases. What is about 
the case of having a SVC or any other layered media, where one session 
SB contains the base layer and another session SE contains the 
enhancement layer. Let us assume session SB is protected by  repair flow 
RB. Furthermore, session SB and SE are jointly protected by repair flow 
RB+E. Additionally, RB+E is additive to RB. The only way expressing this 
with the current draft seems to be:

        a=group:FEC-XR SB RB
        a=group:FEC-XR SB SE RB RB+E

I would expect that the grouping can signal that RB can be used 
separately for SB, but RB and RB+E can be also jointly used for the 
combination of SB and SE. Would the above grouping be in line with the 
current draft? I wonder if this may be somehow contrary to definition in 
section 4.1:

"Repair flows that are in different FEC groups are non-
   additive.".

If the signaling in the example above is in line with the intention of 
the draft, I would make the following modifications:

- You may add an "...exclusively in different FEC groups..." to the 
sentence of section 4.1 above.
- Further, I would add the following text to section 4.1 to make it clearer:

"In order to express multiple relations between source and repair flows, 
source and repair flows may appear in more than one FEC group."

I think the same should be valid for the FEC-SSRC grouping.

Best regards,
Thomas

-- 
Thomas Schierl
--------------
Fraunhofer HHI

Jean-Francois Mule wrote:
> This is to start a 2-week working group last call on draft
> draft-ietf-mmusic-rfc4756bis-03,
> http://tools.ietf.org/html/draft-ietf-mmusic-rfc4756bis-03.  The comment
> period will end on Wednesday October 28.
>
> Please send your comments to the mmusic list and the authors.
>
> Thank you,
> Jean-Francois.
>
>
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