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Re: [tsvwg] Gorry Fairhurst Individual thoughts on choosing whether/how to advance ECN work.

Pete Heist <pete@heistp.net> Fri, 15 May 2020 22:14 UTC

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From: Pete Heist <pete@heistp.net>
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Date: Sat, 16 May 2020 00:14:51 +0200
Cc: Joseph Touch <touch@strayalpha.com>, paul@redbarn.org, Gorry Fairhurst <gorry@erg.abdn.ac.uk>, "tsvwg@ietf.org" <tsvwg@ietf.org>
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References: <dbc71da6-70f1-7369-1d2d-f08fb3b08b69@erg.abdn.ac.uk> <999D213E-D708-4189-990E-1801F8C6E814@strayalpha.com> <3CD6E65D-3D28-49E3-B77C-4C3CCC155BA4@gmail.com> <EAA264BA-E9A5-4E1B-A934-6104A0976DF9@strayalpha.com> <08EBD982-0D17-4F75-97F8-F09D873AECDC@gmail.com>
To: Jonathan Morton <chromatix99@gmail.com>
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Subject: Re: [tsvwg] Gorry Fairhurst Individual thoughts on choosing whether/how to advance ECN work.
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> On May 15, 2020, at 10:38 PM, Jonathan Morton <chromatix99@gmail.com> wrote:
> 
>> On 15 May, 2020, at 10:50 pm, Joseph Touch <touch@strayalpha.com> wrote:
>> 
>> Is there a brief summary of what you wrote?
>> 
>> I.e., in 1-2 short sentences each:
> 
>> 	- assuming endpoints lie and/or network nodes lie (either by what they indicate or what they rewrite), are either of these options still safe?
> 
> I believe SCE is safe under the assumption of lying endpoints and/or middleboxes, to approximately the same extent that RFC-3168 ECN is.  Either the lie has a benign effect, or it ultimately harms the liar, for each class of possible lie that has been brought to my attention.
> 
> Conversely, it is straightforward to demonstrate a case in L4S where lying gains a significant advantage for the liar: a sender may mark its traffic ECT(0) but then implement DCTCP-style congestion control.  The demonstrated in-network component of L4S does not protect against this, and at least some existing networks are also vulnerable to it.

For a test result along these lines, the plot below shows CUBIC vs Prague when:
1) disabling bottleneck detection (a module parameter) and
2) using an iptables rule to change ECT(1) to ECT(0) on outgoing TCP segments without the SYN flag sent

http://sce.dnsmgr.net/results/ect1-2020-05-15T235113-s10-gaming-ect1-ect0/l4s-s10-gaming-ect1-ect0/l4s-s10-gaming-ect1-ect0-ns-cubic-vs-prague-dualpi2-20ms_tcp_delivery_with_rtt.svg

Capture files and so forth are here:

http://sce.dnsmgr.net/results/ect1-2020-05-15T235113-s10-gaming-ect1-ect0/l4s-s10-gaming-ect1-ect0/

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