Re: [quicwg/base-drafts] Behavior around key availability delays during handshake (#3874)

Kazuho Oku <notifications@github.com> Thu, 20 August 2020 05:43 UTC

Return-Path: <noreply@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 428D43A0789 for <quic-issues@ietfa.amsl.com>; Wed, 19 Aug 2020 22:43:57 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.101
X-Spam-Level:
X-Spam-Status: No, score=-3.101 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, HTML_MESSAGE=0.001, MAILING_LIST_MULTI=-1, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, 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 5aPXhKbfKheH for <quic-issues@ietfa.amsl.com>; Wed, 19 Aug 2020 22:43:56 -0700 (PDT)
Received: from out-20.smtp.github.com (out-20.smtp.github.com [192.30.252.203]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id E6DCA3A077A for <quic-issues@ietf.org>; Wed, 19 Aug 2020 22:43:55 -0700 (PDT)
Received: from github-lowworker-f1f7af9.ash1-iad.github.net (github-lowworker-f1f7af9.ash1-iad.github.net [10.56.111.13]) by smtp.github.com (Postfix) with ESMTP id 39210E1E34 for <quic-issues@ietf.org>; Wed, 19 Aug 2020 22:43:55 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=github.com; s=pf2014; t=1597902235; bh=sKsKJrwGw7XKk7b7HeXDTyzczbef6uwvXRn4Au4ueXA=; h=Date:From:Reply-To:To:Cc:In-Reply-To:References:Subject:List-ID: List-Archive:List-Post:List-Unsubscribe:From; b=WPMY+xJJkJX1PAUnW49pzHDnaSjDy7AnepYz+xwjnGrzxTCiZkNsEqgu56j1QFJ1u bTdbCaGHcy8fa87uTcCdE6z8pqLHq5x7WDXgp4LVtyjW1/DXqo8xsunNyWJDUDwdaH o9hsRMgdiNiZnUn//eU0YA78KgbFJ222ssZhXe9s=
Date: Wed, 19 Aug 2020 22:43:55 -0700
From: Kazuho Oku <notifications@github.com>
Reply-To: quicwg/base-drafts <reply+AFTOJKYCZTNSK3JQ3MXHLLV5JHXJXEVBNHHCN3MY3A@reply.github.com>
To: quicwg/base-drafts <base-drafts@noreply.github.com>
Cc: Subscribed <subscribed@noreply.github.com>
Message-ID: <quicwg/base-drafts/pull/3874/review/471258517@github.com>
In-Reply-To: <quicwg/base-drafts/pull/3874@github.com>
References: <quicwg/base-drafts/pull/3874@github.com>
Subject: Re: [quicwg/base-drafts] Behavior around key availability delays during handshake (#3874)
Mime-Version: 1.0
Content-Type: multipart/alternative; boundary="--==_mimepart_5f3e0d9b29373_6ee91964355139"; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: list
X-GitHub-Sender: kazuho
X-GitHub-Recipient: quic-issues
X-GitHub-Reason: subscribed
X-Auto-Response-Suppress: All
X-GitHub-Recipient-Address: quic-issues@ietf.org
Archived-At: <https://mailarchive.ietf.org/arch/msg/quic-issues/Z0R0_XW3pTFbC5EczRMPDQMLrRs>
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: Thu, 20 Aug 2020 05:43:57 -0000

@kazuho commented on this pull request.



> @@ -348,6 +348,11 @@ acknowledgement delays are likely to be non-repeating and limited to the
 handshake. The endpoint can therefore use them without limiting them to the
 max_ack_delay, avoiding unnecessary inflation of the RTT estimate.
 
+Ignoring max_ack_delay at the beginning of the connection can lead to a
+substantially inflated smoothed_rtt. Therefore, prior to handshake confirmation,

I do not think that this sentence is correct. Ignoring `max_ack_delay` is a way to prevent inflation of SRTT. The problem here is that ignoring `max_ack_delay` is not enough, if `min_rtt` is not established.

> +The calculation of smoothed_rtt uses RTT samples after adjusting them for
+acknowledgement delays. These delays are computed using the ACK Delay field of
+the ACK frame as described in Section 19.3 of {{QUIC-TRANSPORT}}.
+
+The peer might report acknowledgement delays that are larger than the peer's
+max_ack_delay during the handshake (Section 13.2.1 of {{QUIC-TRANSPORT}}). To
+account for this, the endpoint SHOULD ignore max_ack_delay until the handshake
+is confirmed (Section 4.1.2 of {{QUIC-TLS}}). When they occur, these large
+acknowledgement delays are likely to be non-repeating and limited to the
+handshake. The endpoint can therefore use them without limiting them to the
+max_ack_delay, avoiding unnecessary inflation of the RTT estimate.
+
+Ignoring max_ack_delay at the beginning of the connection can lead to a
+substantially inflated smoothed_rtt. Therefore, prior to handshake confirmation,
+an endpoint MAY ignore RTT samples if subtracting the acknowledgement delay
+causes the sample to be less than the min_rtt.

I'm not sure if I follow this sentence. I thought that adjusted_rtt can never become smaller than min_rtt, and that would continue to be the case with this PR?

-- 
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/3874#pullrequestreview-471258517