[Codel] fq_Codel vs Sfq_Codel

Dave Taht dave.taht at gmail.com
Sat Feb 28 12:58:53 EST 2015

sfq_codel in ns2 is derived more from SFQ than DRR, and there are
several substantial differences, although sfq_codel  can be almost,
but not quite, configured to act the same as the dual DRR version that
is in the actual, shipping, fq_codel. The version of DRR fq_codel uses
is more similar to "DRR+" and "DRR++", but is uniquely it's own.

You have to use sfq_codel VERY carefully in the ns2 version, as the
ability to correctly generate a five tuple hash is not there.
Correctly generating a 5 tuple is almost, but not quite, in the ns3
version, last I looked, and that ns3 version is MUCH closer to the
actual fq_codel version deployed in the field, but still not quite the
same thing.  I have kind of lost track as to the right ns2 and ns3
versions to start from, also. Tom?

in terms of setting up realistic scenarios: A common (actually, nearly
universal) change to fq_codel in the field at low bandwidths (below
50mbit) is to use a reduced quantum (300 bytes). I don't remember how
to do that right in the ns2 version. It has, after all, been 3 years
of no interest from the academic community. Also the codel target and
interval need to be tuned slightly, at below 2.5mbits to account for a
single full length packet at those speeds.

I am delighted by the sudden upsurge in interest in the *fq_codel
versions but I would certainly appreciate more efforts on making the
underlying simulations actually match the deployment, before everyone
goes off writing papers again.

See sch_fq_codel.c in the linux distributions since 3.6, see also
codel.h there, and compare against what you have for ns2 and ns3.

I completely lack time or funding to make sims match the (much better
reality) at this point. Worst case, I would encourage you to test the
sims verses the deployed code with the same exact tests, so you can
see what differences exist.

On Sat, Feb 28, 2015 at 9:34 AM, divya singla <divyasingla1989 at gmail.com> wrote:
> can anybody tell me is there any difference between fq_Codel and Sfq_Codel?
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> Codel mailing list
> Codel at lists.bufferbloat.net
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Dave Täht
Let's make wifi fast, less jittery and reliable again!


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