[134012] in North American Network Operators' Group
Re: TCP congestion control and large router buffers
daemon@ATHENA.MIT.EDU (Sam Stickland)
Tue Dec 21 14:22:48 2010
In-Reply-To: <alpine.DEB.1.10.1012210758140.27193@uplift.swm.pp.se>
Date: Tue, 21 Dec 2010 19:21:58 +0000
From: Sam Stickland <sam_mailinglists@spacething.org>
To: Mikael Abrahamsson <swmike@swm.pp.se>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On 21 Dec 2010, at 07:18, Mikael Abrahamsson <swmike@swm.pp.se> wrote:
On Mon, 20 Dec 2010, Jim Gettys wrote:
Common knowledge among whom? I'm hardly a naive Internet user.
Anyone actually looking into the matter. The Cisco "fair-queue" command was
introduced in IOS 11.0 according to <
http://www.cisco.com/en/US/docs/ios/12_2/qos/command/reference/qrfcmd1.html#wp1098249>
to somewhat handle the problem. I have no idea when this was in time, but I
guess early 90:ties?
200ms is good; but it is often up to multiple *seconds*. Resulting latencies
on broadband gears are often horrific: see the netalyzr plots that I posted
in my blog. See:
I know of the problem, it's no news to me. You don't have to convince me.
I've been using Cisco routers as a CPE because of this for a long time.
Interestingly I've just tried to enable WRED on a Cisco 877 (advsecurity
15.1) and the random-detect commands are missing. Cisco's feature navigator
says it's supported though. Weird.
Also, there doesn't appear to be a way to enable fair-queue on the wireless
interface. Is fair-queue seen as a bad strategy for wireless and it's
varying throughput/goodput rates?
And finally it doesn't support inbound shaping so I can't experience with
trying to build the queues on it rather than the DSLAM.
I'm a little nonplussed to be honest.
However, I did notice the output queue on the dialler interface defaults to
1000 packets. (Perhaps that's a hangover from when it had to queue packets
whilst dialling? I've come too late to networking to know). Reducing that
number to 10 (~60ms @ 1500 bytes @ 8Mbps) has noticeably increased the
latency response and fairness of the connection under load.
Sam
