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

Colin Perkins <csp@csperkins.org> Thu, 30 June 2016 14:51 UTC

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From: Colin Perkins <csp@csperkins.org>
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References: <ccf9f2d7-2694-4336-0ec9-ccfebfeb0120@ericsson.com> <CE03DB3D7B45C245BCA0D243277949362F585D3E@MX307CL04.corp.emc.com> <d97e30a7-70f5-26d0-c3a4-0497c669f5f6@ericsson.com> <CE03DB3D7B45C245BCA0D243277949362F586054@MX307CL04.corp.emc.com> <D19E595F-7C66-4AE9-92B4-D550A93F634D@csperkins.org> <CE03DB3D7B45C245BCA0D243277949362F589335@MX307CL04.corp.emc.com> <20160616222548.GB77166@verdi> <0643E158-BF26-4692-8167-B7A959CB20CE@csperkins.org> <CE03DB3D7B45C245BCA0D243277949362F596DBC@MX307CL04.corp.emc.com> <E16BEA87-1D0F-48F1-A9AC-2729079D581D@tik.ee.ethz.ch> <8C16F1C6-B4A7-4BB4-B215-D7E7EAF308F8@erg.abdn.ac.uk> <CE03DB3D7B45C245BCA0D243277949362F59C41D@MX307CL04.corp.emc.com> <3E053A65-2698-4749-8E3D-E0451DF84011@ifi.uio.no> <BF6B00CC65FD2D45A326E74492B2C19FB76A6433@FR711WXCHMBA05.zeu.alcatel-lucent.com> <32a23d69d22062669f78df806a4eb6b8.squirrel@erg.abdn.ac.uk> <BF6B00CC65FD2D45A326E74492B2C19FB76A659B@FR711WXCHMBA05.zeu.alcatel-lucent.com> <CE03DB3D7B45C245BCA0D24327! ! 79493 62F5 AEE02@MX307CL04.corp.emc.com> <6E35FB6C-CA98-413C-B7AE-75402A968017@ifi.uio.no> <3FD27BBF-8E2D-4A42-86A0-C4C0692FF8C9@csperkins.org> <A1874131-D163-4740-98B9-61F055230A04@ifi.uio.no> <CE03DB3D7B45C245BCA0D243277949362F5AFAE1@MX307CL04.corp.emc.com> <2E09525C-C1AD-41D1-AE22-865518FA0FBE@csperkins.org> <DD563445-98AD-43F1-8AB8-3E70FDC8F9F1@ifi.uio.no> <CE03DB3D7B45C245BCA0D243277949362F5B4628@MX307CL04.corp.emc.com> <CBC76076-8D5D-4BC8-87E6-6FC07620BB27@ifi.uio.no>
To: Michael Welzl <michawe@ifi.uio.no>
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Cc: "Black, David" <david.black@emc.com>, "rtcweb@ietf.org" <rtcweb@ietf.org>, tsvwg <tsvwg@ietf.org>, IETF AVTCore WG <avt@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 15:54, Michael Welzl <michawe@ifi.uio.no>; wrote:
>> 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….

Does anyone have data to let us find out either way? 

>> 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”

If the congestion control is working, then it should adapt the rate so the circuit breaker never triggers. Yes, there should be a parallel congestion control, but for the circuit breaker to be relevant, that congestion control is either not working properly, or not implemented. 

-- 
Colin Perkins
https://csperkins.org/