Re: [Bloat] RED against bufferbloat

["Toke Høiland-Jørgensen" <toke@toke.dk>]

Michael Welzl <michawe@ifi.uio.no> writes:

> but that's FQ (or FQ_CoDel's changed FQ variant), much more than the
> AQM mechanism in use (as we have also seen presented by Toke at the
> last ICCRG meeting).

Well, actually, that presentation did also include an evaluation of the
AQMs in an asymmetrical scenario. And that shows that while generally
ARED does perform fairly well, it tends to be a bit on the aggressive
side. In the asymmetrical case this results in too many drops on the
slow side of the asymmetrical link (typically upload), hurting throughput
in the other direction due to lost ACKs.

There's also some other issues in there, with PIE and CoDel in
particular, most notably their reactions when conditions change: it can
take tens of seconds for the algorithms to get queueing latency under
control in this case.

Slides for the IETF presentation available here:
http://www.ietf.org/proceedings/91/slides/slides-91-iccrg-4.pdf

There's also a longer version of the talk (from the Stanford Netseminar)
available on Youtube: https://www.youtube.com/watch?v=kePhqfKA3SM

> But this discussion is about AQM mechanisms, not (changed)FQ.

While the academic side of me enjoys studying AQMs (and I'm still far
from anything resembling a thorough understanding of them), the
practical "I just want my network to work" side of me has become
increasingly convinced (in part by doing the experiments in the above
mentioned talk) that FQ is more important than AQM in many scenarios. As
such, I think that excluding FQ from the conversation is mostly of, well,
academic interest ;)

-Toke