Subject: Re: [rtcweb] CNAMEs and multiple peer connections
From: Magnus Westerlund <[email-masked]>
To: Martin Thomson <[email-masked]>, Dan Wing <[email-masked]>
Cc: "[email-masked]" <[email-masked]>
Date: Mon, 10 Mar 2014 15:42:12 +0100
List-Id: Real-Time Communication in WEB-browsers working group list <rtcweb.ietf.org>

On 2014-03-08 07:48, Martin Thomson wrote:
> On 7 March 2014 20:14, Dan Wing <[email-masked]> wrote:
>> About half a year ago, AVTCORE published an updated recommendation
>> for CNAME as RFC7022.  Is its guidance insufficient?
> 
> Necessary, but not sufficient.  Unfortunately, the definition of a 
> "session", while sufficient for the description in 7022, is not
> quite precise enough for this use case.  The implication there is
> that it means "RTP session", which is both not at the right level of 
> granularity, and not directly actionable.

So, within a PeerConnection one have one or more RTP sessions, depending
on how one configures it. That RTP session MAY be interconnected with
other PeerConnection's RTP sessions by a middlebox.

As long as this is different end-points PCs there is little issues. The
interesting case here is if one end-point connects multiple PCs to the
same middlebox and starts seeing its own traffic due to the middlebox
not being built for this usage and the JS programmer thinks this is okay
to do.

The end-point can always detect this, as it knows all its used CNAMEs,
and can note that they are looped back to itself if this check is
implemented. If one have the same CNAME is both PC's RTP session
instances the RTP stack is more likely to detect this without code
changes as a loop.

The only reason I can see for having multiple PCs being connected to the
same middlebox would be if that makes the setup of QoS simpler, but I
think MST individual RTP sessions within the context of one PC is more
straight forward to ensure that one have unique 5-tuples per media stream.

> 
> I also note this little gem:
> 
> A longer-term persistent RTCP CNAME is sometimes useful to
> facilitate third-party monitoring, consistent with [RFC3550].

Yes, but that is clearly not suitable for WebRTC.

Cheers

Magnus Westerlund

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