Re: [rtcweb] BUNDLE with implicit rtcp-mux

[Magnus Westerlund <[e-mail]>]

On 2014-03-10 09:24, Christer Holmberg wrote:
> Hi,
> 
>  
> 
> Before I comment on your proposal, let’s take a few steps back (maybe it
> can even solve your issue).
> 
>  
> 
> BUNDLE currently mandates the usage of both the SDP rtcp-mux and rtcp
> attributes. I remember we had discussions about that, but I don’t
> remember the justification at the moment. But, I wonder whether that
> text is from before we made a decision that, unless both endpoints
> support BUNDLE, no endpoint will use a single address:port.
> 
>  
> 
> So, the question is: do we really need the SDP rtcp attribute?

I think it is a question of how you want the fallback to work. In the
case of bundle only lines, a non  bundle supporting peer will reject
them, thus no issues with what is written around RTCP-mux and a=rtcp in
those m= blocks. However, the first one if you want that to support
fallback that makes sense then you will need both a=rtcp-mux and an
a=rtcp (with a different port) to handle that with optimal backwards
compatibility.

Regarding the motivation for a=rtcp-mux and a=rtcp, I think it is
reasonably straight forward. We want a=rtcp-mux to minimize port usage,
i.e. ports=1. Not supporting a=rtcp-mux with bundle that would mean two
ports (RTP and RTCP) for the bundle group. To get the backwards
compatibility the usage of a=rtcp would be required.

Cheers

Magnus Westerlund

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