Re: [rtcweb] Plan A, respun

[Colin Perkins <[e-mail]>]

On 8 May 2013, at 12:00, Harald Alvestrand wrote:
> The paragraph that worries me most is this one:
> 
>    Offerers conformant to this specification MUST do one of the
>    following:
> 
>    o  Use non-overlapping PT values for each m-line in any given bundle
>       group.
> 
>    o  Provide distinct a=ssrc attributes for each m-line which uses
>       overlapping PT values with any other m-line.  [Technically, this
>       is a general case of the previous point.]
> 
> To put a blunt point on it: Either send less than ~32 streams, or give a=ssrc attributes.
> 
> To me, that measn we're mandating one mechanism (PT values) for small numbers of flows, and another mechanism (a=ssrc) for large numbers of flows - such mechanism changes usually have "interesting" properties in what happens at the changeover point.
> 
> It would seem to me to be architecturally cleaner to insist that a=ssrc be used always.

I agree: the PT was never intended to be used as a demultiplexing point for different flows in RTP, that's the role of the SSRC. An a=ssrc: line, or an RTCP SDES item, can then be used to bind the SSRC to an m= line, or some other higher-layer identifier. 

-- 
Colin Perkins
http://csperkins.org/