[133614] in North American Network Operators' Group
RE: TCP congestion control and large router buffers
daemon@ATHENA.MIT.EDU (Mikael Abrahamsson)
Tue Dec 14 12:50:45 2010
Date: Tue, 14 Dec 2010 18:50:36 +0100 (CET)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: George Bonser <gbonser@seven.com>
In-Reply-To: <5A6D953473350C4B9995546AFE9939EE0B14CF14@RWC-EX1.corp.seven.com>
Cc: nanog@nanog.org, Sam Stickland <sam@spacething.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Tue, 14 Dec 2010, George Bonser wrote:
> that sort of delay. Some form of AQM is probably a good thing as would
> be the wider use of ECN. Finding out that a buffer filled and a packet
> (or many packets) was dropped five seconds after the fact, isn't going
ECN pretty much needs WRED, and then people need to implement that first.
The only routing platform I know to support it is 7200 and the other types
of cpu routers from Cisco running fairly recent IOS (seems to have been
introduced in 12.2T).
http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ftwrdecn.html
> You need enough buffering to satisfy packets "in flight" for a
> connection on the other side of the planet but man, what he has been
> reporting is just insane and it would be no wonder performance can be
> crap.
Yeah, 30-60ms of buffering is what I have favoured so far.
With L2 switches you don't get anywhere near that, but on the other side a
few ms of buffering+tail drop has much less impact on interactive
applications compared to seconds of buffering.
--
Mikael Abrahamsson email: swmike@swm.pp.se
