[Tmrg] Proposal to increase TCP initial CWND
fred at cisco.com (Fred Baker) Tue, 20 July 2010 15:13 UTC
From: "fred at cisco.com"
Date: Tue, 20 Jul 2010 08:13:19 -0700
Subject: [Tmrg] Proposal to increase TCP initial CWND
In-Reply-To: <AANLkTilUcGqwMWkMRYfUiXSf5uAXnFPxKfgGlKa-TW-F@mail.gmail.com>
References: <AANLkTil937lyUzRvUtdqd2qdl9RN7AZ-Mo_cT-dtmqXz@mail.gmail.com> <923833DA-FC31-4D30-96A5-48D4D072DBD3@cisco.com> <AANLkTimFEGfPJo9rjTw6oNPmwuHkEFBmAX1Ps2yYsUWh@mail.gmail.com> <67225862-FF5A-4B3B-B681-C07E5A705B35@cisco.com> <AANLkTilUcGqwMWkMRYfUiXSf5uAXnFPxKfgGlKa-TW-F@mail.gmail.com>
Message-ID: <E7E5F841-C9F0-46CD-974C-FA3D38997E9C@cisco.com>
I'm sure that for the user in question, user completion time was faster with a higher initial window, for the simple reason that the first few RTTs are fully used. That's non-responsive to the question that Lachlan raised yesterday and which I commented on, which is "how does that affect other traffic". On Jul 19, 2010, at 8:25 PM, Jerry Chu wrote: > On Mon, Jul 19, 2010 at 7:11 AM, Fred Baker <fred at cisco.com> wrote: >> >> "Typical" varies by vendor and software implementation. On Cisco products, the default IOS configuration gives 40 buffers in the queue. > > Thanks for the data. So a "typical" dialup link can easily accommodate a couple > of simultaneously IW=10 flows, but will likely drops pkts for the more > aggressive > services that open more than 3 connections, each will full load. > > We recently setup a small testbed to try to evaluate the effect of > IW=10 in various > scenarios. The test results are still preliminary but like what we expected, in > many contentious cases pkt retransmission rates are higher for IW=10 compared > to IW=3. But in most cases the "user completion time" for IW=10 still beat out > that of IW=3. It looks like pkt drops don't necessitate lower performance. > In the IW=10 cases the saving in the roundtrips more than compensate for the > extra roundtrips to recover lost pkts. Here every pkt and flow are accounted for > so there is no hidden "victim" flow. > > Jerry > >> >> On Jul 19, 2010, at 1:12 AM, Jerry Chu wrote: >> >>> On Sat, Jul 17, 2010 at 11:53 PM, Fred Baker <fred at cisco.com> wrote: >>>> >>>> This is essentially the point of concern I raised to them; I also raised the point that what works well in the broadband Internet is quite a bit different than Internet access in parts of the world that have slower typical access rates. >>> >>> I'd like to point out Google's services are not restricted to just >>> broadband users. Also from our experiements >>> some of the greatest latency improvments of a larger IW seem to have >>> come from users behind slow or highly >>> multiplexed links. >>> >>> Do you know how much buffer space a typical dial-up (e.g., 56Kbps) >>> access router provides? >>> >>> Jerry >>> >>>> >>>> On Jul 17, 2010, at 11:27 PM, Lachlan Andrew wrote: >>>> >>>>> - An increase in retransmissions from 3.94% to 5.79% seems very >>>>> significant, if that rate reflects the loss rate. Although described >>>>> as a 1.85% increase, it seems likely to cause competing traffic to >>>>> slow down by a factor of sqrt(5.79/3.94). Moreover, that is the >>>>> increase in loss when (presumably) a *single* flow on that bottleneck >>>>> increases its initial window. How can we estimate the impact of *all* >>>>> flows increasing their initial windows? >>>> >>>> http://www.ipinc.net/IPv4.GIF >>>> >> >> http://www.ipinc.net/IPv4.GIF >> http://www.ipinc.net/IPv4.GIF
- [Tmrg] Proposal to increase TCP initial CWND Lachlan Andrew
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Lachlan Andrew
- [Tmrg] Proposal to increase TCP initial CWND SCHARF, Michael
- [Tmrg] Proposal to increase TCP initial CWND Aleksandar Milenkoski
- [Tmrg] Proposal to increase TCP initial CWND Lachlan Andrew
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Stefan Hirschmann
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Lachlan Andrew
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Stefan Hirschmann
- [Tmrg] Proposal to increase TCP initial CWND Stefan Hirschmann
- [Tmrg] Proposal to increase TCP initial CWND Fred Baker
- [Tmrg] Proposal to increase TCP initial CWND Yuchung Cheng
- [Tmrg] Proposal to increase TCP initial CWND Lachlan Andrew