Re: [rtcweb] CNAMEs and multiple peer connections

Magnus Westerlund <> Wed, 12 March 2014 08:29 UTC

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Date: Wed, 12 Mar 2014 09:29:35 +0100
From: Magnus Westerlund <>
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Subject: Re: [rtcweb] CNAMEs and multiple peer connections
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On 2014-03-10 16:49, Martin Thomson wrote:
> On 10 March 2014 16:19, Magnus Westerlund
> <> wrote:
>> Can you please think through the linkage issue a bit first before
>> changing this property.
> We already came to the conclusion that if media was being forwarded by
> a peer, then that is new media originated by that peer, not the same
> media.  Thus, if looping occurs, it is at the application layer.  We
> definitely already agreed that RTP forwarding is not a function that a
> browser will support.

I like to point out that the agreement and what is documented in
rtp-usage is that WebRTC endpoint will have to make forwarded streams
appear as locally originated. However, this as currently written does
not apply to RTP middleboxes that interconnects multiple PeerConnections
to form a multi-party session. This is deliberate to ensure that RTP
topologies like RTP mixer and SFM do work on the RTP/RTCP level.

> Obviously, if we add that feature, CNAMEs will be just one of the
> manifold issues that will arise and we will have to reconsider.
> Compromising the privacy of users doesn't seem like a good trade-off
> against some minor advantages in terms of loop detection (unlikely)
> and synchronization (easy to apply manually).

I am especially interested to know how you will "easy to apply manually"
the synchronization. Can you please describe that. Because, that either
requires an API call to tell the media framework, please consider the
following CNAMES as equivalent, or some other method of telling the
media framework that these different MST are actually originating from a
common clock base.

I protested about this, not to lower the users privacy, but over the
concern that this was raised without providing a case where it was
obvious that the user's privacy was impacted. Martin, you said that you
would think about it, and the next statement was lets change it, without
providing any motivation why the concern was significant.

>From my perspective, if you can provide a good explanation how to
actually accomplish the synchronization, I think a change of scoping the
CNAME to a PeerConnection is okay. But, I would like to understand how
you believe it is accomplished.

Magnus Westerlund
(As RTP-usage author)

Services, Media and Network features, Ericsson Research EAB/TXM
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