Subject: Re: [aqm] AQM BoF - RTGAREA slides

From: Mikael Abrahamsson <[email-masked]>
Date: Fri, 9 Aug 2013 17:55:09 +0200 (CEST)

On Tue, 30 Jul 2013, Scharf, Michael (Michael) wrote:

> I am just curious: Is there any data that shows *any* benefit of RED (or 
> whatever other AQM flavor) on a 10G or 100G link?

As opposed to FIFO? I'd say that if you made a platform with 600ms buffer 
and tried to cram 130 gigabit/s of data through it, I'm sure RED would 
be of benefit.

Not a data point, but I have some experience with (accidentally) 
saturating links with a lot of traffic. For instance a 1G link (10 years 
ago when gig was fast) that when it was flatlining didn't have more than 
approximately 5-10ms worth of buffers, then would tail drop. This was 
still usable when congesting, when (later) there was approximately 1.3 
gigabit/s of traffic after upgrade to 10GE, so approximately 30% 
backpressure.

I've seen 1G links on "real" core routers with 600ms buffers and back in 
the days with mostly Win98, Win2k and XP clients you would see 10-20 ms of 
buffers because the clients didn't have more than 16-64k TCP windows, so 
it would hold stable at 10-20ms buffering and zero loss.

Current core routers seem to have converged onto around 50ms of buffers 
and I think this makes a lot of sense. If I had a bit more time and 
equipment I'd really like to test a theory of mine, and that is to try to 
run thousands of TCP sessions through a 100GE link (10GE might be enough) 
with RED set at 0% loss 0-5ms buffer depth drop and then from 5-50 ms 
buffer depth ramp up from 0 to 100%. I woud also like to experiment with 
that 100% at 50ms set to decrements of 10. My theory is that 10% drop 
probability at 50ms depth might be enough to make TCP never reach this 
point in a sustained fashion.

-- 
Mikael Abrahamsson    email: [email-masked]