Re: [aqm] Question re draft-baker-aqm-recommendations recomendation #4

Scott Brim <swb@internet2.edu> Fri, 12 July 2013 13:16 UTC

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Date: Fri, 12 Jul 2013 09:15:42 -0400
From: Scott Brim <swb@internet2.edu>
Organization: Internet2
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To: Bob Briscoe <bob.briscoe@bt.com>
References: <8C48B86A895913448548E6D15DA7553B850ECE@xmb-rcd-x09.cisco.com> <41E8D91E-658B-4B44-92D2-5EB0329781A5@ifi.uio.no> <20130506191725.GV23227@verdi> <6CCF558E-975C-4C86-9D67-CA431CC6FBA1@ifi.uio.no> <201307120122.r6C1MlTD026331@bagheera.jungle.bt.co.uk>
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Cc: "Fred Baker (fred)" <fred@cisco.com>, aqm@ietf.org
Subject: Re: [aqm] Question re draft-baker-aqm-recommendations recomendation #4
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On 07/11/13 21:22, Bob Briscoe allegedly wrote:
> Fred,
> 
> At 15:00 06/05/2013, Fred Baker (fred) wrote:
>> Do we generally agree with the recommendation of
>> http://tools.ietf.org/html/draft-baker-aqm-recommendation-01#section-4.4?
>> This is the question of ensuring that AQM technologies are applicable
>> to all Internet traffic - not just TCP, but UDP, SCTP, and so on.
> 
> I'm not as much a fan of recommendation #4 as everyone else seems to be.
> I think it's a wordsmithing issue, not fundamental.
> 
> I suggest wording such as: "AQMs SHOULD allow congestion controls to
> remain as effective as they are with other widely accepted AQMs or with
> tail drop."
> 
> Reasoning: An AQM can't be effective with all transports, because
> congestion control is achieved by the e2e transport, not the AQM alone.

Bob, that's the meaning of SHOULD: do it ... unless there's a good
reason why not (and explain why not).  Different transports use
different algorithms.  Your rephrasing looks to be closer to a MUST.

> "All transports" includes:
> * unresponsive transports that aren't trying to be effective,
> * and delay-based transports like VEGAS & LEDBAT that don't work well in
> some circumstances.

To the extent that AQM applies, it should be effective.  If it's not
relevant, then that's a good reason not to, i.e. "SHOULD" applies.

> The suggested wording makes it clear we're talking about criteria for
> testing AQMs against transports that we already know are able to be
> effective. Not about the AQM forcing a 'normal' congestion control
> behaviour even if the congestion control doesn't want to play, or
> 'normal' has been redefined.
> 
> The reason I care about the wording here is that some may read this as a
> licence to include per-flow rate policing within the AQM (cf AFD,
> XCHOKe, etc). I strongly believe that per-flow rate policers SHOULD NOT
> be in /every/ AQM.

Is this a slippery slope argument?  If we allow it at all it will infect
everything and ruin our great nation?  I don't believe this group is
going to agree on a single algorithm. :-)

Scott