Re: [aqm] TCP ACK Suppression

Christian Huitema <> Fri, 09 October 2015 02:08 UTC

Return-Path: <>
Received: from localhost ( []) by (Postfix) with ESMTP id C96581A8724 for <>; Thu, 8 Oct 2015 19:08:43 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2.002
X-Spam-Status: No, score=-2.002 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001] autolearn=ham
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id CwFqrWgUVWoy for <>; Thu, 8 Oct 2015 19:08:42 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id E0DC51A86E3 for <>; Thu, 8 Oct 2015 19:08:40 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=selector1; h=From:To:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=ilbpr+lVIhPauU7l1UgB9+t7atZrceU418UZkvW7TO0=; b=NapqWQeur0qDCq5Am+HQzfS2UNkHU6rOx74MAJ32L/vFgdEBeAPR4AgONlzOxb9ArQ2EhntEVuG9zse/36pnKkD2rZSXuKvlb94yxxDKykx0QmjhU+kbkGWv+RO4FY83x1ypE7Qv5JnbRpuzydJaU4/y+dJD5VKi4IAdUZNuRR8=
Received: from ( by ( with Microsoft SMTP Server (TLS) id; Fri, 9 Oct 2015 02:08:37 +0000
Received: from ([]) by ([]) with mapi id 15.01.0293.007; Fri, 9 Oct 2015 02:08:37 +0000
From: Christian Huitema <>
To: David Lang <>
Thread-Topic: [aqm] TCP ACK Suppression
Date: Fri, 9 Oct 2015 02:08:37 +0000
Message-ID: <>
References: <> <> <> <> <> <> <> <> <> <> <>
In-Reply-To: <>
Accept-Language: en-US
Content-Language: en-US
authentication-results: spf=none (sender IP is );
x-originating-ip: []
x-microsoft-exchange-diagnostics: 1; DM2PR0301MB0655; 5:RB580HuYBTRJyYuHKOKX1wvb7J448i1IB0+kdWraNc+OW3Gtyg8CO6v7Rt/cOzi97tgVuuJDGCR7reJQ1hBqiXI+dhip5LJVbBMa+PjMO7MVsDY1/16ZDrowwOAqSih2WgJ/8QGU4KJarChHu1e95g==; 24:poC+AdB+1uHAiNIn/FPjEFI8dKvOQlr1Zlaz1F26yj/xIo7NSO91Ka1ZU4x7hGBaY+Pekw3mGeCkL4blssjCLLDDzZPpl7ekNHDI6SZ2apA=; 20:qjfFPoVmHJ20t1sXChWSIosmsrXd9AZYw0TNX3OjhAPKTqgSKAONHwTvlOnsER3sA7UPZbAOonCkVjEy4X5mrw==
x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:DM2PR0301MB0655;
x-o365eop-header: O365_EOP: Allow for Unauthenticated Relay
x-o365ent-eop-header: Message processed by - O365_ENT: Allow from ranges (Engineering ONLY)
x-microsoft-antispam-prvs: <>
x-exchange-antispam-report-test: UriScan:;
x-exchange-antispam-report-cfa-test: BCL:0; PCL:0; RULEID:(61425024)(601004)(2401047)(8121501046)(5005006)(520078)(3002001)(61426024)(61427024); SRVR:DM2PR0301MB0655; BCL:0; PCL:0; RULEID:; SRVR:DM2PR0301MB0655;
x-forefront-prvs: 0724FCD4CD
x-forefront-antispam-report: SFV:NSPM; SFS:(10019020)(6009001)(199003)(377454003)(189002)(24454002)(101416001)(87936001)(76176999)(64706001)(54356999)(33656002)(92566002)(2950100001)(2900100001)(74316001)(66066001)(102836002)(5003600100002)(93886004)(50986999)(77096005)(40100003)(122556002)(46102003)(99286002)(86612001)(10090500001)(5002640100001)(5001960100002)(76576001)(97736004)(189998001)(5004730100002)(110136002)(8990500004)(5007970100001)(11100500001)(106356001)(86362001)(81156007)(10290500002)(105586002)(10400500002)(5005710100001)(106116001)(5008740100001)(217873001); DIR:OUT; SFP:1102; SCL:1; SRVR:DM2PR0301MB0655;; FPR:; SPF:None; PTR:InfoNoRecords; A:1; MX:1; LANG:en;
received-spf: None ( does not designate permitted sender hosts)
spamdiagnosticoutput: 1:23
spamdiagnosticmetadata: NSPM
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Oct 2015 02:08:37.2490 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM2PR0301MB0655
Archived-At: <>
Cc: "LAUTENSCHLAEGER, Wolfram \(Wolfram\)" <>, Greg White <>, "" <>, Joe Touch <>
Subject: Re: [aqm] TCP ACK Suppression
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: "Discussion list for active queue management and flow isolation." <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Fri, 09 Oct 2015 02:08:44 -0000

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?

> 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...

-- Christian Huitema