Re: [aqm] Question re draft-baker-aqm-recommendations recomendation #2

Wesley Eddy <> Tue, 30 April 2013 17:50 UTC

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Date: Tue, 30 Apr 2013 13:49:43 -0400
From: Wesley Eddy <>
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Subject: Re: [aqm] Question re draft-baker-aqm-recommendations recomendation #2
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On 4/30/2013 1:05 PM, Fred Baker (fred) wrote:
> Hmm. Maybe I should separate them into separate recommendations.
> Yes, I think ECN has the built-in possibility of an end system using
> the flag to gain what it thinks is some variation on preference - it
> can get one more packet into a queue than it would if it didn't
> advertise an ECN capability, but it doesn't actually implement RFC
> 3168 etc. At some point, one has to drop even ECN-capable traffic.
> Not for AQM reasons; for defensive reasons.
> I have, and dare I say "we have", observed several implementations
> that have tried the approach of bending the rules to gain preference.
> BitTorrent did so by having multiple parallel aggressive TCP-like
> connections; we all know the outcome of that - multiple connections
> is fine, but bulldozing networks is a good way to get yourself
> bulldozed. One TCP implementation I know of did away with slow start
> and congestion control altogether. Guess what happened; a repeat of
> the 56 KBPS NSFNET in a more confined environment. If such
> implementations become at all widespread, and that one did within the
> company that wrote it, it gets to compete with itself, and it's not a
> pretty sight. There are other ways to deal with that kind of thing
> than "we who are wise thumb our collective noses in your general
> direction". In the end, money talks, and customers prefer networks
> that work and transport implementations that work in those networks.
> I personally don't have a problem with the *ability* to configure
> something; where I think we have issues is the *necessity*. On your
> other questions, I might refer you to the sixth recommendation; if we
> don't have papers that tell us that, let's write some.

This all makes sense to me.  I definitely think that splitting /
factoring-out the part about reverting to tail-drop is a good idea.

Note that if you have the ability to configure something, it should
be necessary for some sane default to be available, either so that
you don't have to touch it, or can easily revert back after you make
the mistake of touching it.

Wes Eddy
MTI Systems