[tsvwg] draft-ietf-tcpm-accurate-ecn-09: AccECN option: why not EE1B first?

Neal Cardwell <ncardwell@google.com> Mon, 11 November 2019 17:25 UTC

Return-Path: <ncardwell@google.com>
X-Original-To: tsvwg@ietfa.amsl.com
Delivered-To: tsvwg@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 0C2F7120AAD for <tsvwg@ietfa.amsl.com>; Mon, 11 Nov 2019 09:25:28 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -17.501
X-Spam-Level:
X-Spam-Status: No, score=-17.501 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_MED=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, ENV_AND_HDR_SPF_MATCH=-0.5, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, USER_IN_DEF_DKIM_WL=-7.5, USER_IN_DEF_SPF_WL=-7.5] autolearn=unavailable autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=google.com
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 FVy7ehtejR-Q for <tsvwg@ietfa.amsl.com>; Mon, 11 Nov 2019 09:25:23 -0800 (PST)
Received: from mail-oi1-x22d.google.com (mail-oi1-x22d.google.com [IPv6:2607:f8b0:4864:20::22d]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 666CB120AA0 for <tsvwg@ietf.org>; Mon, 11 Nov 2019 09:25:20 -0800 (PST)
Received: by mail-oi1-x22d.google.com with SMTP id 22so12170480oip.7 for <tsvwg@ietf.org>; Mon, 11 Nov 2019 09:25:20 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:from:date:message-id:subject:to; bh=ujKHauN5wOYauyxS2y5qXYrM7e7WOKPqIKbiQX1RyOw=; b=cvxBoUqe6zGCqA3ldLHhMTXi6wNRQ0Pk+s/wPjMHG/B1NY8jUyOL/3YAsWEBknjtzJ CZxbguhP2u7R1Ll00+y1RNNGcoIcjp4lH/RVpXH1tkUREApzeq+AU4zDVlG54q1wRO7h 6REBneldU4qbD4phFsQ76i+L+R3sVxO2HuWZw6WmYFBZ+npAcdJa4lXfFjcfwSd5+un/ xvLBoARCqZIjU083RXJ4M4ZMI/29jcebjQ3JZYWQW8E/JIiOZqvhBvVe+FFzrqcp7VMa zi2mPYsKeCBjvYfUF/gH9+pj4zuZW4lIvHXef4jD8eQd4c2Pi5BGW/I0yWNeD5axAikY HB2g==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:from:date:message-id:subject:to; bh=ujKHauN5wOYauyxS2y5qXYrM7e7WOKPqIKbiQX1RyOw=; b=Q2VX3R1Ml+V0xJQZldrRGZstSAJIl9Y8gcjfZOw6nsSI46PLbruwbs6uYm4cDMeZrb Ch3F5SlfIVY04ezzxctfjzNwmnLc2utTfveOmtOTXPiqavFD34ARoa7NWjnR88bOtlWC NN4745LO58/KKxcCw/7LvFfElWXN1EDUQ9E5I3RfLawnYmEtvroqPhBhETZffPJd5egx r8EwXtZgihJAbE6hzBJKxq/GbhA1va0DUPcJrYU3RwRO6+yEQRyvLxx64hXAMh8bGCoZ 2SvySvdM2v4i5Fl/yTv60qeNG34Y6vUIHXKn9GqlmLrnQTYiPY+FuwhIOwZDKnqI3XJ5 lMrA==
X-Gm-Message-State: APjAAAU8bwBxCNhwH3ZHNReCmsjitrB65X+TiwarC/7EZ2C9h4ZYbA/g gdchIaH0LxpuLC7tg2XHeiDBA15uE+B1lvrFiqkeww==
X-Google-Smtp-Source: APXvYqwuAZxQJYmyb4URajn0mJJ7bBJL2gtyLMQRhE43tdgB+N/Z25+kv9LtdoCpZckD9wpbBuVlmJSELlTCLjwAqJA=
X-Received: by 2002:aca:d90a:: with SMTP id q10mr56577oig.129.1573493119163; Mon, 11 Nov 2019 09:25:19 -0800 (PST)
MIME-Version: 1.0
From: Neal Cardwell <ncardwell@google.com>
Date: Mon, 11 Nov 2019 12:25:02 -0500
Message-ID: <CADVnQykh-MjnfzNtRQ22fwxUS3BY_YOJOPghV9B08s+dN9G17Q@mail.gmail.com>
To: Bob Briscoe <research@bobbriscoe.net>, tsvwg IETF list <tsvwg@ietf.org>, "tcpm@ietf.org" <tcpm@ietf.org>
Content-Type: text/plain; charset="UTF-8"
Archived-At: <https://mailarchive.ietf.org/arch/msg/tsvwg/Gpx7OAfdGsKGDLjutaDto-I50m4>
Subject: [tsvwg] draft-ietf-tcpm-accurate-ecn-09: AccECN option: why not EE1B first?
X-BeenThere: tsvwg@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Transport Area Working Group <tsvwg.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tsvwg>, <mailto:tsvwg-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tsvwg/>
List-Post: <mailto:tsvwg@ietf.org>
List-Help: <mailto:tsvwg-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tsvwg>, <mailto:tsvwg-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 11 Nov 2019 17:25:28 -0000

A particular question in regards to the AccECN option:

  https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-09#section-3.2.6

The AccECN option spec lists the EE0B field first, with the EE1B field
at the end.

Given that L4S plans on using ECT(1) for data packets, and unchanging
counter values can be omitted from the end of the AccECN option, why
not list EE1B first, and EE0B last? With EE1B first and EE0B last it
seems that in the common case for an L4S connection the (unchanged)
EE0B could be omitted, allowing 4 extra bytes of payload per packet.
AFAICT this extra 4 bytes would increase goodput for applications
using IPv4 or IPv6 with an MTU of 1500 by about 0.3%, by my
back-of-the-envelope calculations.

best,
neal