Re: [aqm] think once to mark, think twice to drop: draft-ietf-aqm-ecn-benefits-02

Vishal Misra <misra@cs.columbia.edu> Fri, 27 March 2015 18:45 UTC

Content-Type: multipart/alternative; boundary="Apple-Mail=_7AB2110E-B20F-4309-ABD7-354CABC81559"
Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2090\))
From: Vishal Misra <misra@cs.columbia.edu>
In-Reply-To: <20150327183659.GI39886@verdi>
Date: Fri, 27 Mar 2015 14:45:13 -0400
Message-Id: <72C12F6B-9DDE-4483-81F2-2D9A0F2D3A48@cs.columbia.edu>
References: <23AFEFE3-4D93-4DD9-A22B-952C63DB9FE3@cisco.com> <BF6B00CC65FD2D45A326E74492B2C19FB75BAA82@FR711WXCHMBA05.zeu.alcatel-lucent.com> <72EE366B-05E6-454C-9E53-5054E6F9E3E3@ifi.uio.no> <55146DB9.7050501@rogers.com> <08C34E4A-DFB7-4816-92AE-2ED161799488@ifi.uio.no> <BF6B00CC65FD2D45A326E74492B2C19FB75BAFA0@FR711WXCHMBA05.zeu.alcatel-lucent.com> <alpine.DEB.2.02.1503271024550.2416@nftneq.ynat.uz> <5d58d2e21400449280173aa63069bf7a@hioexcmbx05-prd.hq.netapp.com> <20150327183659.GI39886@verdi>
To: John Leslie <john@jlc.net>
Archived-At: <http://mailarchive.ietf.org/arch/msg/aqm/wE3-rPiXh3LneclVobHCdFUVDZ4>
Cc: "Scheffenegger, Richard" <rs@netapp.com>, aqm@ietf.org
Subject: Re: [aqm] think once to mark, think twice to drop: draft-ietf-aqm-ecn-benefits-02
Precedence: list

If you reduce latency, the dynamics of TCP are such that it will necessarily increase loss rate. On a bottlenecked link, the relationship of throughput to the RTT and loss rate of TCP is roughly the following (happy stop supply link to papers):

throughput = K/(RTT*sqrt(p))

where K is some constant, p is the loss rate and RTT is the round trip time. If you reduce latencies, to maintain the same throughput (that of the bottlenecked link), the loss rate has to necessarily go up.
So reducing latencies has the impact of increasing loss rates which affects things in bad ways as has been pointed out.

With ECN, it is the _marking_ rate that goes up and TCP follows the same dynamics. Nothing is dropped, no harm done.
That’s why ECN widely adopted is a win-win.

-Vishal
--
http://www.cs.columbia.edu/~misra/

> On Mar 27, 2015, at 2:36 PM, John Leslie <john@jlc.net> wrote:
> 
> Scheffenegger, Richard <rs@netapp.com <mailto:rs@netapp.com>> wrote:
>> 
>> ... At the least when you are using TCP, a drop will cause head-of-line
>> blocking on the receiver, for at least 1 RTT;
> 
>   Yes.
> 
>   This is a trade-off: many folks believe that a good AQM has enough
> benefits for typical TCP flows to overcome that. (YMMV)

[aqm] review of draft-ietf-aqm-ecn-benefits-02 Fred Baker (fred)
[aqm] think once to mark, think twice to drop: dr… De Schepper, Koen (Koen)
Re: [aqm] think once to mark, think twice to drop… Michael Welzl
Re: [aqm] think once to mark, think twice to drop… David Collier-Brown
Re: [aqm] think once to mark, think twice to drop… Michael Welzl
Re: [aqm] think once to mark, think twice to drop… De Schepper, Koen (Koen)
Re: [aqm] think once to mark, think twice to drop… David Lang
Re: [aqm] think once to mark, think twice to drop… Scheffenegger, Richard
Re: [aqm] think once to mark, think twice to drop… John Leslie
Re: [aqm] think once to mark, think twice to drop… Vishal Misra
Re: [aqm] think once to mark, think twice to drop… David Lang
Re: [aqm] think once to mark, think twice to drop… David Lang
Re: [aqm] think once to mark, think twice to drop… KK
Re: [aqm] think once to mark, think twice to drop… David Lang
Re: [aqm] think once to mark, think twice to drop… Vishal Misra
Re: [aqm] think once to mark, think twice to drop… Scheffenegger, Richard
Re: [aqm] think once to mark, think twice to drop… De Schepper, Koen (Koen)
Re: [aqm] think once to mark, think twice to drop… David Lang
Re: [aqm] think once to mark, think twice to drop… Bob Briscoe
Re: [aqm] think once to mark, think twice to drop… David Lang
Re: [aqm] think once to mark, think twice to drop… John Leslie
[aqm] Gaming ECN (again) (was: think once to mark… Bob Briscoe
Re: [aqm] Gaming ECN (again) (was: think once to … David Lang