Re: [aqm] [tcpm] TCP ACK Suppression

David Lang <david@lang.hm> Mon, 12 October 2015 00:10 UTC

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From: David Lang <david@lang.hm>
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To: Jonathan Morton <chromatix99@gmail.com>
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Cc: "tcpm@ietf.org" <tcpm@ietf.org>, Joe Touch <touch@isi.edu>, "mallman@icir.org" <mallman@icir.org>, "LAUTENSCHLAEGER, Wolfram \(Wolfram\)" <wolfram.lautenschlaeger@alcatel-lucent.com>, Greg White <g.white@cablelabs.com>, "aqm@ietf.org" <aqm@ietf.org>
Subject: Re: [aqm] [tcpm] TCP ACK Suppression
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On Mon, 12 Oct 2015, Jonathan Morton wrote:

>> My contention is that since this is already happening, consolidating the
> ACK packets into stretched ACKs doesn't make this any worse, and it saves
> network bandwidth (and decreases latency to the extent that data is acked
> faster than waiting for the entire chain or original ACKs to get through,
> especially if that would take multiple transmit windows). As a result,
> thinning the ACKs is kinder to the network.
>
> I agree, *iff* they are not DupACKs signalling packet loss.  Do existing
> and future cable modems take that subtle distinction into account?

I don't know, and RFC3449 section 5.2.1 lists a couple other conditions to 
watch out for. But this discussion started with what AQM algorithms can/should 
do when they see multiple ACKs in their queue (and I added wifi as part of 
make-wifi-fast). So we are talking about what should be put in future code. The 
cable modems are just an example we can draw from of a past implementation of 
similar ideas.

hopefully future cable modems will use a more generic AQM algorithm instead of 
the hard-coded optimizations they've had in the past. It's almost always a win 
when a generic solution can replace a specific solution :-)

David Lang