Re: [Dart] ICE might send your traffic over TCP

"Black, David" <david.black@emc.com> Thu, 24 July 2014 13:25 UTC

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From: "Black, David" <david.black@emc.com>
To: Jonathan Lennox <jonathan@vidyo.com>
Date: Thu, 24 Jul 2014 09:25:30 -0400
Thread-Topic: ICE might send your traffic over TCP
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Subject: Re: [Dart] ICE might send your traffic over TCP
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> I don't think different drop precedences would be useful in respect to TCP.

Clarification: "in respect to TCP" -> "within a single TCP connection".

IMHO, Ruediger's larger overall point is valid:

> > It may make sense to have different TCP flows marked by different drop
> precedences. The less important TCP flows get throttled in the case of
> congestion.

Thanks,
--David


> -----Original Message-----
> From: Dart [mailto:dart-bounces@ietf.org] On Behalf Of Jonathan Lennox
> Sent: Thursday, July 24, 2014 9:01 AM
> To: Ruediger.Geib@telekom.de
> Cc: dart@ietf.org
> Subject: Re: [Dart] ICE might send your traffic over TCP
> 
> I don't think different drop precedences would be useful in respect to TCP.
> 
> The problem is that the way the WebRTC APIs are structured, it's not
> necessarily clear to an application that its media traffic is indeed going
> over TCP, so it might make precedence requests that the browser implementing
> the APIs can't (and shouldn't try to) satisfy.
> 
> The question is how the browser should behave when that happens.  I spoke to
> Cullen about this, offline, after the DART session, and I believe he had a
> simple proposal.
> 
> On Jul 24, 2014, at 3:54 AM, Ruediger.Geib@telekom.de wrote:
> 
> > Jonathan,
> >
> > Let's briefly discuss your point below: Different drop precedences are
> required if congestion within a PHB group may occur. TCP is designed for
> reliable transport. In case of a loss, TCP will reduce bandwidth and
> retransmit the dropped information. I'm not an RTP expert. The few
> applications known to me don't seem to benefit from such a behavior, if a
> single application flow uses different drop precedence levels in combination
> with TCP.
> >
> > It may make sense to have different TCP flows marked by different drop
> precedences. The less important TCP flows get throttled in the case of
> congestion. But is there a need to avoid re-ordering across different drop
> precedences, which is an AF PHB group feature? Again, I'm not an RTP expert -
> but that doesn't sound like making a lot of sense too.
> >
> > In general, I'd be interested to learn, if some applications were
> benefitting from ECN (or a congestion indication by marking rather than by
> dropping). Independent from the question whether they use TCP or RTP
> transport.
> >
> > Regards,
> >
> > Ruediger
> >
> >
> >
> >
> > -----Message-----
> > From: Dart [mailto:dart-bounces@ietf.org] On behalf of Jonathan Lennox
> > Subject: [Dart] ICE might send your traffic over TCP
> >
> > [snip]
> >
> > How (say) a WebRTC implementation should handle API requests for multiple
> drop precedences when the underlying ICE channel is TCP is unclear to me.
> >
> > Jonathan Lennox
> >
> >
> 
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