Re: [AVTCORE] [rtcweb] [tsvwg] WG Last Call on changes: draft-ietf-avtcore-rtp-circuit-breakers-16

Michael Welzl <michawe@ifi.uio.no> Wed, 29 June 2016 14:54 UTC

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From: Michael Welzl <michawe@ifi.uio.no>
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Date: Wed, 29 Jun 2016 16:54:09 +0200
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To: "Black, David" <david.black@emc.com>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/avt/BeUlTbtPEDAe19VaL1hWcBSunh0>
Cc: "rtcweb@ietf.org" <rtcweb@ietf.org>, Colin Perkins <csp@csperkins.org>, IETF AVTCore WG <avt@ietf.org>, tsvwg <tsvwg@ietf.org>
Subject: Re: [AVTCORE] [rtcweb] [tsvwg] WG Last Call on changes: draft-ietf-avtcore-rtp-circuit-breakers-16
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> On 29. jun. 2016, at 16.44, Black, David <david.black@emc.com>; wrote:
> 
> I wrote: 
> 
>>> Another possible rationale for this mixing is that if drops start occurring, then many of
>>> the new and proposed uses of ECN that treat ECN-CE marks as less than loss-equivalent
>>> are outside their intended operating envelopes/regions.
> 
> Colin responded:
> 
>> Clearly if the queue has been driven to overflow, so that packet loss is
>> occurring, then the AQM is outside its intended operating regime. I’m not sure
>> we need to push it so far, though. Is there not a regime where the ECN-CE
>> marking rate indicates excessive congestion, before the queue overflows and
>> drops packets?
> 
> Yes, but that may not be relevant to this discussion.   My hypothesis for this discussion
> is that actual drops will occur well before RTP  is running at 10x the TCP equivalent rate
> (based on drops and ECN-CE marks), and that 10x factor is the trip threshold for the
> circuit breaker, which is the focus of this discussion. 
> 
> I would think that the "regime where the ECN-CE marking rate indicates excessive
> congestion, before the queue overflows and drops packets?" would not extend as
> far as RTP running at 10x the TCP equivalent rate, which is where the RTP circuit
> breaker trips.

Seems reasonable to me….

> 
> This is all a thought exercise - I'm happy to be shown to be wrong based on actual
> data and experience with "running code" ...
> 
> To which Michael responded: 
> 
>> Shouldn’t a congestion control mechanism react well before that?
> 
> Yes, if there is one ;-).  This is RTP …

Earlier, in the same conversation, so - I assume - the same context, Colin wrote:
"Assuming, in all cases, that there’s a parallel congestion control algorithm running”

Cheers,
Michael