Re: [aqm] TCP ACK Suppression

Joe Touch <touch@isi.edu> Fri, 09 October 2015 17:59 UTC

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To: David Lang <david@lang.hm>
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From: Joe Touch <touch@isi.edu>
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Cc: "LAUTENSCHLAEGER, Wolfram \(Wolfram\)" <wolfram.lautenschlaeger@alcatel-lucent.com>, Greg White <g.white@CableLabs.com>, "tcpm@ietf.org" <tcpm@ietf.org>, "aqm@ietf.org" <aqm@ietf.org>, touch@isi.edu
Subject: Re: [aqm] TCP ACK Suppression
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Dave in particular wanted some specific reasons this is a bad idea as
presented. Here is my summary.

The rest of this discussion should happen on TCPM.

Joe

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1) *you* shouldn't be using a mechanism that destroys information for others

	whether the timestamps or ACK stream spacing has any
	meaning is for the receiver - not you - to decide

2) *you* don't know where your mechanism will have an impact

	those clumped ACKs might be spaced out further
	downstream

	even if you have a rule of "I'll only gather 3 ACKs",
	you can't know if another box - including yours -
	downstream might gather those composite ACKs further

3) you claim this might be safe *if* AQM is widely deployed

	but *you* don't appear to be making that determination
	*before* deploying your approach

	also, AQM is in the opposite direction, and unless
	you deploy this with enough state to track the fact
	that your box is seeing traffic in both directions,
	you shouldn't be turning it on at all

As others have noted, the SHOULD of ACK requirements can be exceeded,
but only with careful consideration of the potential impact. That
careful consideration does not consist of "I turned it on and I didn't
hear anyone scream".

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