Re: [quicwg/base-drafts] Persistent Congestion Time Threshold (#2365)

ianswett <notifications@github.com> Wed, 30 January 2019 12:38 UTC

Return-Path: <bounces+848413-a050-quic-issues=ietf.org@sgmail.github.com>
X-Original-To: quic-issues@ietfa.amsl.com
Delivered-To: quic-issues@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 706D31295D8 for <quic-issues@ietfa.amsl.com>; Wed, 30 Jan 2019 04:38:22 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -7.553
X-Spam-Level:
X-Spam-Status: No, score=-7.553 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-4.553, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=github.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 aqmbt360oJMp for <quic-issues@ietfa.amsl.com>; Wed, 30 Jan 2019 04:38:19 -0800 (PST)
Received: from o1.sgmail.github.com (o1.sgmail.github.com [192.254.114.176]) (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 718241294FA for <quic-issues@ietf.org>; Wed, 30 Jan 2019 04:38:19 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d=github.com; h=from:reply-to:to:cc:in-reply-to:references:subject:mime-version:content-type:content-transfer-encoding:list-id:list-archive:list-post:list-unsubscribe; s=s20150108; bh=nvF2e+HRJqOxLBaPHOLjzzcJRa4=; b=YlqUkmFgwGBB+PjX QDfnyW7KDQcbBQl6iLrs96JDJDKI7GPZfO8V48aWvRN23FM9B017euBsUDJPodTO 713AXzynBlfoutQtKZ6+BKFSlEv8QD9gQ7fPp7nhGbak2c5B6zqf7WUxCZ36xUP7 nfrCaQ7difl/HgWcfAZtxPJp4WE=
Received: by filter1055p1las1.sendgrid.net with SMTP id filter1055p1las1-13803-5C519ABA-28 2019-01-30 12:38:18.536462953 +0000 UTC m=+125002.524514820
Received: from github-lowworker-baaab27.cp1-iad.github.net (unknown [192.30.252.33]) by ismtpd0026p1iad2.sendgrid.net (SG) with ESMTP id hJEZDIc5QLuBmbmEDgohZQ for <quic-issues@ietf.org>; Wed, 30 Jan 2019 12:38:18.389 +0000 (UTC)
Received: from github.com (localhost [127.0.0.1]) by github-lowworker-baaab27.cp1-iad.github.net (Postfix) with ESMTP id 5216080274 for <quic-issues@ietf.org>; Wed, 30 Jan 2019 04:38:18 -0800 (PST)
Date: Wed, 30 Jan 2019 12:38:18 +0000
From: ianswett <notifications@github.com>
Reply-To: quicwg/base-drafts <reply+0166e4ab0c171bab31a62d5d3463049f2fc4a73bd9f8fe5f92cf0000000118695cba92a169ce17fab1f6@reply.github.com>
To: quicwg/base-drafts <base-drafts@noreply.github.com>
Cc: Subscribed <subscribed@noreply.github.com>
Message-ID: <quicwg/base-drafts/pull/2365/review/198054430@github.com>
In-Reply-To: <quicwg/base-drafts/pull/2365@github.com>
References: <quicwg/base-drafts/pull/2365@github.com>
Subject: Re: [quicwg/base-drafts] Persistent Congestion Time Threshold (#2365)
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="--==_mimepart_5c519aba4eb7c_5c823ff7e16d45c074367"; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: list
X-GitHub-Sender: ianswett
X-GitHub-Recipient: quic-issues
X-GitHub-Reason: subscribed
X-Auto-Response-Suppress: All
X-GitHub-Recipient-Address: quic-issues@ietf.org
X-SG-EID: l64QuQ2uJCcEyUykJbxN122A6QRmEpucztpreh3Pak2IEiV5ZBOE5vHcF+/PLhh5TwexfWwl+/CLN7 /Ds4MfAuCp9tAbfUJ+skSnln4eE6ZHQnCbeBy/Vb12sUZGvYBKUjC4bFVL9qJKiMhswDWQJ20/KzQ4 SUt+QILDZg4bjv0Ffy1rDgZ/RxrapUbRMJg5cxJAM/xZkUaOCz3hyMzZ97bkd9gVfjhTmjnXwdB4Hc o=
Archived-At: <https://mailarchive.ietf.org/arch/msg/quic-issues/Oz1-4TeT_4saeIhgzG3t2hMU5k4>
X-BeenThere: quic-issues@ietf.org
X-Mailman-Version: 2.1.29
List-Id: Notification list for GitHub issues related to the QUIC WG <quic-issues.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/quic-issues>, <mailto:quic-issues-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/quic-issues/>
List-Post: <mailto:quic-issues@ietf.org>
List-Help: <mailto:quic-issues-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/quic-issues>, <mailto:quic-issues-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 30 Jan 2019 12:38:22 -0000

ianswett commented on this pull request.



>  When an ACK frame is received that establishes loss of all in-flight packets
-sent prior to a threshold number of consecutive PTOs (pto_count is more than
-kPersistentCongestionThreshold, see {{cc-consts-of-interest}}), the network is
-considered to be experiencing persistent congestion, and the sender's congestion
-window MUST be reduced to the minimum congestion window (kMinimumWindow).  This
-response of collapsing the congestion window on persistent congestion is
-functionally similar to a sender's response on a Retransmission Timeout (RTO) in
-TCP {{RFC5681}}.
+sent over a long enough period of time, the network is considered to be
+experiencing persistent congestion.  Commonly, this can be established by
+consecutive PTOs, but since the PTO timer is reset when a new ack-eliciting
+packet is sent, an explicit duration must be used to account for those cases
+where PTOs do not occur or are substantially delayed.  This duration is the
+equivalent of kPersistentCongestionThreshold consecutive PTOS, smoothed_rtt +
+4 * rttvar + max_ack_delay * ((2 ^ kPersistentCongestionThreshold) - 1).

Q for here and below: Should max_ack_delay be added after exponential backoff, instead of before?  Adding it after incentivizes implementations to indicate a realistic value, since an unrealistic one just adds to rttvar, which seems desirable.

-- 
You are receiving this because you are subscribed to this thread.
Reply to this email directly or view it on GitHub:
https://github.com/quicwg/base-drafts/pull/2365#pullrequestreview-198054430