Re: [aqm] [tcpm] TCP ACK Suppression

David Lang <david@lang.hm> Sat, 10 October 2015 02:15 UTC

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From: David Lang <david@lang.hm>
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To: 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>, "mallman@icir.org" <mallman@icir.org>
Subject: Re: [aqm] [tcpm] TCP ACK Suppression
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On Fri, 9 Oct 2015, Joe Touch wrote:

> On 10/9/2015 5:22 PM, David Lang wrote:
>> You don't want to acknowlege it, but TCP is broken in the face of
>> excessive buffering.
>
> Arguably, buffering was broken and failed to provide the feedback to TCP
> (see next paragraph)
>
>> TCPM isn't fixing that, grassroots efforts are
>> developing the fixes and AQM is formalizing the results.
>
> TCPM fixed it in 2001 by providing the flags for ECN, which was enabled
> by default in Windows since 2012. ALTQ support for ECN has been around
> for nearly that long.
>
> What's changed? Not the TCP reaction (except in extreme cases such as
> for datacenters) but the router algs. And getting the router algs into
> routers - esp. home devices.

if ECN solved the problem, then bufferbloat would have been a non-issue. A large 
percentage of the home routers are running OpenWRT or similar with ECN enabled. 
That didn't solve the problem.

>> TCP is also broken in the face of current and within-the-next-year
>> future wifi technologies. AQM helps some here, and there is again
>> outside efforts to address the problem. TCPM hasn't done anything that
>> I've heard of other than possibly say that the network technology is
>> broken and shouldn't be used.
>
> You might start tracking the TCPM list. We've been talking today about
> how to reduce the ACKs by direct action of the source.

There are only so many lists I can track (linux kernel takes a lot of time for 
example :-), I'll consider it.

The problem with proposals like that is just like RFC3449 says, the source can't 
know what the network looks like to decide if there is a benefit to reducing 
ACKs.

David Lang