[tcpm] Review of hystartplusplus-01

" Ilpo Järvinen " <ilpo.jarvinen@cs.helsinki.fi> Wed, 22 January 2020 12:24 UTC

Return-Path: <ilpo.jarvinen@cs.helsinki.fi>
X-Original-To: tcpm@ietfa.amsl.com
Delivered-To: tcpm@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 93396120089 for <tcpm@ietfa.amsl.com>; Wed, 22 Jan 2020 04:24:27 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -4.301
X-Spam-Level:
X-Spam-Status: No, score=-4.301 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_MED=-2.3, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (1024-bit key) header.d=cs.helsinki.fi
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 e8HXbVGxCpOj for <tcpm@ietfa.amsl.com>; Wed, 22 Jan 2020 04:24:24 -0800 (PST)
Received: from script.cs.helsinki.fi (script.cs.helsinki.fi [128.214.11.1]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id BFA3D120077 for <tcpm@ietf.org>; Wed, 22 Jan 2020 04:24:24 -0800 (PST)
X-DKIM: Courier DKIM Filter v0.50+pk-2017-10-25 mail.cs.helsinki.fi Wed, 22 Jan 2020 14:24:18 +0200
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cs.helsinki.fi; h=date:from:to:subject:message-id:mime-version:content-type; s= dkim20130528; bh=aO/tytD3HXEwb9grga+Ktogl8lscaCUy1XFrnFfGBpo=; b= HLnwcark6VzVTLDOKpzvyqVJbVypj81FLX3IVswEeEnxpphTeqyMwieRBoPMoSUZ aeTD1S0oIITyGi6CQo8keIeeiZr/Hfo4hNWwM5TrX9ojq5q4zu8HwCnNxYwuT4cH BK2d1ows/a1wLpUWOaelvL7OWMFR44c2kWMhmH7NqSI=
Received: from whs-18.cs.helsinki.fi (whs-18.cs.helsinki.fi [128.214.166.46]) (TLS: TLSv1/SSLv3,256bits,AES256-GCM-SHA384) by mail.cs.helsinki.fi with ESMTPS; Wed, 22 Jan 2020 14:24:18 +0200 id 00000000005A0170.000000005E283EF2.00001BF7
Date: Wed, 22 Jan 2020 14:24:18 +0200
From: Ilpo Järvinen <ilpo.jarvinen@cs.helsinki.fi>
X-X-Sender: ijjarvin@whs-18.cs.helsinki.fi
To: tcpm@ietf.org, pravb@microsoft.com, huanyi@microsoft.com, maolson@microsoft.com
Message-ID: <alpine.DEB.2.20.2001221413070.25645@whs-18.cs.helsinki.fi>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Archived-At: <https://mailarchive.ietf.org/arch/msg/tcpm/luEXF0gYKd8Y5aj5ywl-Ghb7OsE>
Subject: [tcpm] Review of hystartplusplus-01
X-BeenThere: tcpm@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: TCP Maintenance and Minor Extensions Working Group <tcpm.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tcpm>, <mailto:tcpm-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tcpm/>
List-Post: <mailto:tcpm@ietf.org>
List-Help: <mailto:tcpm-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tcpm>, <mailto:tcpm-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 22 Jan 2020 12:24:27 -0000

Hi all,

I've just read through the HyStart++ draft v01. Two comments:

I find using variable named "Eta" and related constants (MIN/MAX_ETA) 
somewhat strange as to me ETA reads "estimated time of arrival" which in 
the context didn't seem to make much of a sense.

Then there is a major contradiction within the draft:

if (currentRoundMinRTT >= (lastRoundMinRTT + Eta))
               ssthresh = cwnd
               exit slow start and enter LSS

  "HyStart++ ends when cwnd exceeds ssthresh or when congestion is
   observed."

...ssthresh is set to cwnd when exiting slow start and LSS is entered as 
per the algorithm but the quoted sentence tells that LSS will be 
terminated as soon as cwnd grows any?

-- 
 i.