TCP congestion control and large router buffers

Tue Dec 14 17:50:36 UTC 2010

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 at swm.pp.se