Re: [MMUSIC] BUNDLE/SDP : ISSUE#2: Should BUNDLE allow/disallow SSRC Repetition ?

[Magnus Westerlund <[e-mail]>]

Hi,

See inline on my opinion and thinking around this subject.

On 2013-10-31 05:46, Suhas Nandakumar wrote:
> Hello All
> 
>   Another issue or concern that was brought up is dealing with RFC5576
> SSRC attributes across the BUNDLED m=lines.
> 
> RFC5576 does allow SSRCs to be repeated across the m=lines given that
> each m=line forms a separate RTP Session.
> 
> There were two options suggested in this regard (by Jonathan)
> 
> 1. Don't allow SSRC values to be repeated across the bundled m-lines
>     ==> Assign category NORMAL
> 

Although it will be normal that a specific SSRC value will only be
associated with a specific media description (m= block) there are
counter arguments for why this limitation can't be done.

For example an FEC encoding across multiple SSRCs i.e. RTP packet
streams can be sent in the same RTP session under its own SSRC. That
SSRC may be desirable to reference in all the m= blocks that contributes
to this particular encoding. Note, we really are talking about
referencing the same packet stream from multiple places.

There are likely more cases where this type of need will arise.

> 2. Allow SSRC values to be repeated iff the media stream satisfies more
> than one m=lines, in which case, the individual sources define the behavior
>   ==> We have 3 options here
>    2.1 Assign Category SPECIAL and add explanatory note on possible
> scenarios 
> 

I think this is likely sufficient to solve this case.

>    2.2 Assign Category SPECIAL and propose an update to RFC5576 to
> explain behavior of a=ssrc attributes when multiple m=lines are multiplexed
> 
>    2.3 Define a new category ?? 
> 
> 
> I look forward for your inputs on how do we deal with this issue.

Cheers

Magnus Westerlund

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