Re: [aqm] I-D Action: draft-ietf-aqm-recommendation-04.txt

[Dave Taht <[e-mail]>]

On Thu, May 21, 2015 at 10:18 PM, Simon Barber <[e-mail]> wrote:
> On 5/18/2015 10:00 AM, Dave Taht wrote:
>>
>> LEDBAT was probably my first concern and area of research before entering
>> this project full time. I *knew* we were going to break ledbat, but the two
>> questions were: how badly? (ans: pretty badly) and did it matter? (not that
>> much, compared to saving seconds overall in induced delay)
>
> LEDBAT is about more than just reducing the delay caused by the steam - it's
> also about the bandwidth impact. AQM solves the delay situation, but breaks
> the bandwidth reduction that LEDBAT can achieve today when other traffic is
> present.

In pointing out that paper I have to stress that their "good" ledbat result,
(read the text around table 3)

"was look! it's scavenging!"

And mine was:

"with over 7 seconds of inherent delay on the link!"

Revisiting the data sets with reasonable amounts of buffering on the link,
a correctly functioning tcp stack, and a few other variables more under
control would be good... (much as I pushed for dctcp to be looked at
once real patches landed for it)

... as would investigating actual behavior of ledbat on real links with
aqm and fq technologies on them. While I poked into it quite a lot,
I did not do much more rigorous than observe that web traffic
worked a lot better when torrent was present in a fq/aqm'd environment
and that cubic outcompeted it slightly, generally.

There was supposed to be someone else updating the tcp_ledbat
kernel module we used, but that never got fixed, and it is in a dire
need of update since the change to usec from msec and other
major tcp modifications in the linux kernel.


>
>> while we have long recommended CS1 be set on torrent, it turns out that a
>> lot of gear actually prioritizes that over BE, still. It helps on the
>> outbound where you can still control your dscp settings. Many torrent users
>> have reported just setting their stuff to max outbound and rate limiting
>> inbound, and observing no real effects on their link.
>
>
> Do you have examples of the gear that prioritizes CS1 over best effort? How
> often have you seen it? Did you see it in places where it would be
> important?

Yes. a lot. and yes. More details I can do later.

> Simon



-- 
Dave Täht
Open Networking needs **Open Source Hardware**

https://plus.google.com/u/0/+EricRaymond/posts/JqxCe2pFr67