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

From: Suhas Nandakumar <[email-masked]>
Date: Wed, 30 Oct 2013 21:46:27 -0700

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

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

   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
Suhas

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From: Magnus Westerlund <[email-masked]>
Date: Thu, 31 Oct 2013 08:32:36 +0100

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.
> 

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.

>    2.1 Assign Category SPECIAL and add explanatory note on possible

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
> 

Cheers

Magnus Westerlund

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From: Harald Alvestrand <[email-masked]>
Date: Thu, 31 Oct 2013 08:54:08 +0100

A=ssrc attributes are a class, so a single rule is likely not enough.
Suggest NORMAL as default with a note that individual attributes may be
designated SPECIAL or identical.
31. okt. 2013 08:31 skrev "Magnus Westerlund" <