Re: [aqm] TCP ACK Suppression

David Lang <david@lang.hm> Fri, 09 October 2015 18:46 UTC

Return-Path: <david@lang.hm>
X-Original-To: aqm@ietfa.amsl.com
Delivered-To: aqm@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 7B8601B4A04 for <aqm@ietfa.amsl.com>; Fri, 9 Oct 2015 11:46:04 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.91
X-Spam-Level:
X-Spam-Status: No, score=-3.91 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, GB_I_LETTER=-2, T_RP_MATCHES_RCVD=-0.01] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id jxEVX9q6vBBZ for <aqm@ietfa.amsl.com>; Fri, 9 Oct 2015 11:46:02 -0700 (PDT)
Received: from bifrost.lang.hm (mail.lang.hm [64.81.33.126]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 96DEB1B49FD for <aqm@ietf.org>; Fri, 9 Oct 2015 11:46:02 -0700 (PDT)
Received: from asgard.lang.hm (asgard.lang.hm [10.0.0.100]) by bifrost.lang.hm (8.13.4/8.13.4/Debian-3) with ESMTP id t99IjsNk023501; Fri, 9 Oct 2015 11:45:54 -0700
Date: Fri, 9 Oct 2015 11:45:54 -0700 (PDT)
From: David Lang <david@lang.hm>
X-X-Sender: dlang@asgard.lang.hm
To: Yuchung Cheng <ycheng@google.com>
In-Reply-To: <CAK6E8=c_h2dMstJSSO9ATh1XUgriWOyeVixk4DHi+PAjO6LSMg@mail.gmail.com>
Message-ID: <alpine.DEB.2.02.1510091144510.3717@nftneq.ynat.uz>
References: <alpine.DEB.2.02.1510060748480.8750@uplift.swm.pp.se> <D2394BB6.548C5%g.white@cablelabs.com> <0A452E1DADEF254C9A7AC1969B8781284A7D9B66@FR712WXCHMBA13.zeu.alcatel-lucent.com> <5616DCD9.8@isi.edu> <alpine.DEB.2.02.1510081428470.3852@nftneq.ynat.uz> <5616E42D.5090402@isi.edu> <alpine.DEB.2.02.1510081517470.3852@nftneq.ynat.uz> <5616FAFA.5020707@isi.edu> <alpine.DEB.2.02.1510081647590.3852@nftneq.ynat.uz> <DM2PR0301MB065553C4CF55E7A6E5E23317A8340@DM2PR0301MB0655.namprd03.prod.outlook.com> <alpine.DEB.2.02.1510081731260.3852@nftneq.ynat.uz> <DM2PR0301MB06554D0E836BC2A8F67E12F2A8340@DM2PR0301MB0655.namprd03.prod.outlook.com> <alpine.DEB.2.02.1510082055510.2943@nftneq.ynat.uz> <CAK6E8=c_h2dMstJSSO9ATh1XUgriWOyeVixk4DHi+PAjO6LSMg@mail.gmail.com>
User-Agent: Alpine 2.02 (DEB 1266 2009-07-14)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII
Archived-At: <http://mailarchive.ietf.org/arch/msg/aqm/c8DVyXVqdoTtsqMVY75EtkftyTY>
Cc: "LAUTENSCHLAEGER, Wolfram \(Wolfram\)" <wolfram.lautenschlaeger@alcatel-lucent.com>, Christian Huitema <huitema@microsoft.com>, Joe Touch <touch@isi.edu>, "aqm@ietf.org" <aqm@ietf.org>, Greg White <g.white@cablelabs.com>
Subject: Re: [aqm] TCP ACK Suppression
X-BeenThere: aqm@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: "Discussion list for active queue management and flow isolation." <aqm.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/aqm>, <mailto:aqm-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/aqm/>
List-Post: <mailto:aqm@ietf.org>
List-Help: <mailto:aqm-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/aqm>, <mailto:aqm-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 09 Oct 2015 18:46:04 -0000

On Fri, 9 Oct 2015, Yuchung Cheng wrote:

> Subject: Re: [aqm] TCP ACK Suppression
> 
> On Thu, Oct 8, 2015 at 9:03 PM, David Lang <david@lang.hm> wrote:
>
>> On Fri, 9 Oct 2015, Christian Huitema wrote:
>>
>> On Thursday, October 8, 2015 5:43 PM, David Lang wrote:
>>>
>>>> ...
>>>> For example, in the fq_codel/cake development, we're finding that there
>>>> are
>>>> some transports that bundle very large numbers of packets together to
>>>> send
>>>> at one time in order to maximize the transport bandwidth. (for example,
>>>> 4x4
>>>> wifi sends a LOT of data in one transmit timeslot). Treating that large
>>>> aggregate as a single packet seriously hurts fairness and latency on the
>>>> next
>>>> hop. So 'pulling apart' this aggregate into the individual
>>>> packets/streams and
>>>> making decisions based on the pieces ends up being a serious win in
>>>> fairness
>>>> and latency.
>>>>
>>>
>>> Define "bundle" please. If they are making sure that several IP packets
>>> are sent back to back in a single Wi-Fi slot, then it is of course
>>> perfectly fine for AQM to handle the IP packets one by one. Does 4x4 Wi-Fi
>>> do something else?
>>>
>>
>> I don't remember the details from the discussion, but the combined bundle
>> required extra steps to pull apart to get at the individual packets. IIRC,
>> not doing so ended up with multi-MB chunks of data to be delivered, which
>> blocked all other traffic while it was being delivered.
>>
>> Suggesting that the queues that build up produce a special enough case to
>>>> consider thinning out the duplicate acks is a far cry from 'making a
>>>> recommendation that breaks other recommendations'
>>>>
>>>
>>> That definitely contradicts the TCP specs. So it is very much in "don't
>>> go there" territory...
>>>
>>
>> By 'not going there' you are crippling people's networks for the sake of
>> following a spec. Rather than following the letter of the old spec, we
>> should be looking at the reasons for it, and reasons to make exceptions.
>> There is a long history of introducing new things that break the old way of
>> doing things, from breaking "classful" network routing to Anycast, there
>> are lots of things that "broke" the old way of doing things.
>>
>> In this case there is more than a decade of people doing exactly what
>> shouldn't even be considered.
>>
>> I'll ask yet again, if acks have already been delayed so that they will be
>> delivered at the same time as later acks, how much value do they actually
>> provide? We need to compare whatever value this is against the cost of the
>> misinformation that they provide, and the impact on other traffic.
>
> Does DOCSIS suppress/filter ACK with SACK blocks and/or ACKs with
> timestamps?

I don't know, but this discussion is not limited to DOCIS.

also, see the other thread covering the RFC discussion. There's a lot more 
details there and in the RFC

David Lang