From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw0-x22a.google.com (mail-yw0-x22a.google.com [IPv6:2607:f8b0:4002:c05::22a]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 068D43B260 for ; Wed, 11 May 2016 10:48:37 -0400 (EDT) Received: by mail-yw0-x22a.google.com with SMTP id j74so44644704ywg.1 for ; Wed, 11 May 2016 07:48:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc; bh=4R35iKX3QZfSsG9qEntCVyHP2tzKAhmLOuibu+famKY=; b=kaogyDHUwRqsvCsfWX7pQLqEJscEEH+KBvU5lxJRmhODx4nMBDUDqgAi0cvhwC1uI9 setfP2hc3uMIn78qq8yXUmOw3A8KXMYZJXHiQLW+ytPKaPZN1f2Kgr+aj5smli6rFiwe ptp6VBIMj3sntXqPfPJwAc8D1Y7LkkVmg1Mgka4d2VHDG0FawMPg+DG+JRwZSLH0ebmm t4d2CzKY6WtL7NRmscS3qRdU5pZoeDBY2A1K+3iF0rOhd8HkeYpCirumtqFYgbpifjoz Yxr3EE9lfR3QpcP5bdTcVjFjeSxv9FiVOaNGuWIZNQKMnSwSGrxQ9zYeruuATeAU6q2L J9iw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc; bh=4R35iKX3QZfSsG9qEntCVyHP2tzKAhmLOuibu+famKY=; b=KCzD0v5D4WrxmLRjZox1/H3FozvA3V83WTjPSwPp2oZKxwDcC02CQI+CpbXIRYt/mI T+ZcfCrQQJwih3fw1uRb3SENEHL607qEhWqvkVesukh2wEDgFtO7GG5xhMkPkaC4Zeha YfM2OiUEzcbgqlTe2X/QDNuM6NYleHNdas/75cRTNpCHeWexHsMLwyjfmfbmCQSTz5u+ aBbM6lR/y1An0HkOl9A+rrqekNtaWkCMHguW5xqmAZNnZ+k6JHrMwalx5d2e+7OywymG vtHufpGouyP3o4nrJwTo6u/RN778iLYTrTa2TY92xvkKtnk5nlC1W7PQ7nxSplVL+XTk hOhQ== X-Gm-Message-State: AOPr4FU8oBgzepgQpr2O+H9kw+Ygq13iWJWrLlHWnJ000VHeyCKm0CoBFDYPKaZnvOVH481/a1MKdDO3TkR6Jw== MIME-Version: 1.0 X-Received: by 10.37.223.14 with SMTP id w14mr1734435ybg.139.1462978116541; Wed, 11 May 2016 07:48:36 -0700 (PDT) Received: by 10.37.74.134 with HTTP; Wed, 11 May 2016 07:48:36 -0700 (PDT) In-Reply-To: <87futolndh.fsf@toke.dk> References: <871t58n5wk.fsf@toke.dk> <87futolndh.fsf@toke.dk> Date: Wed, 11 May 2016 16:48:36 +0200 Message-ID: From: Luca Muscariello To: =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= Cc: make-wifi-fast@lists.bufferbloat.net Content-Type: multipart/alternative; boundary=94eb2c087412f36af305329222b7 Subject: Re: [Make-wifi-fast] Thoughts on tackling airtime fairness X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 11 May 2016 14:48:37 -0000 --94eb2c087412f36af305329222b7 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Wed, May 11, 2016 at 3:45 PM, Toke H=C3=B8iland-J=C3=B8rgensen wrote: > Luca Muscariello writes: > > > Toke, > > > > I'd suggest to add this in you list of references: > > > > Godfrey Tan and John Guttag, Time-based fairness improves performance i= n > multi-rate WLANs. In Proc of USENIX 2004 > > > https://www.usenix.org/legacy/publications/library/proceedings/usenix04/t= ech/general/full_papers/tan/tan.pdf > > Awesome, was not aware of that. Thanks! > > > It's worth having a look to the APware project for freeBSD and Godfrey > Tan PhD thesis at MIT. > > > > http://nms.csail.mit.edu/projects/apware/ > > Hmm, that link is not working for me right now; will try again later. > > > this work predates 802.11n and aggregation. > > Yeah, I'm aware that there is a lot of stuff that predates 802.11n. In > fact the article I linked (Kim et al) is the only one I've found that > talks about 802.11n. We also had some people at my uni doing stuff with > 802.11g. > > > Ten years ago I played with SFQ and madwifi for 802.11g to get max-min > > time fairness (and so proportional rate fairness) with excellent > > results. The hacking I made was based on using time quanta instead of > > bytes. Which required me to get the current PHY rates (AP to all > > STAtions) and dynamically compute/update SFQ time quanta. > > Do you happen to recall what precision you achieved or how much the > precision was really important? Several papers seem to assume that very > high precision is not terribly important since it all evens out in the > end, and I can see how that could be true; but would like to have it > confirmed :) > what do you mean with precision? Do you mean in measuring the PHY rate? Short term vs long term measurements? else? The hard part was adaptiveness. Correlation between the speed of the STA, the PHY rate controller and quanta updates in SFQ. Ideally we were trying to approach something like downlink channel scheduling in HSDPA where you have slotted time TX and polling. A slot in HSDPA (but also LTE) is a burst of fixed time size of several packets. Similar to what you want to achieve in your email point 1. in HSDPA/LTE you have UEs feedback every ms in a side channel. So rate adaptation is a lot simpler. As a side note, there are several differences in aggregates in 802.11n and HSDPA/LTE as in the latter the scheduler can send an aggregate containing packets using different modulation/coding schemes to reach different stations with a single aggregate transmission. For the records, this feature was rejected in the 802.11n amendement but discussed by the group as it makes the chip more expensive. > > > It's surprising that 802.11 standard never considered time fairness in > > the EDCF. A reason might be the time fairness might be enforced using > > the PCF. > > Might be. Might also be that no one thought to measure for that? A lot > of vendors seem to only test single-station raw throughput... > > Are you aware of any open source 802.11 stuff that uses PCF at all? > No. Sorry. > > > IMO, It's a very good topic. > > Thanks for bringing this up. > > You're very welcome! ;) > > -Toke > --94eb2c087412f36af305329222b7 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Wed, May 11, 2016 at 3:45 PM, Toke H=C3=B8iland-J=C3=B8rgensen <toke@tok= e.dk> wrote:
Luca Muscariello <luca.= muscariello@gmail.com> writes:

> Toke,
>
> I'd suggest to add this in you list of references:
>
> Godfrey Tan and John Guttag, Time-based fairness improves performance = in multi-rate WLANs. In Proc of USENIX 2004
> https://www.usenix.org/legacy/publications/library/proceedings= /usenix04/tech/general/full_papers/tan/tan.pdf

Awesome, was not aware of that. Thanks!

> It's worth having a look to the APware project for freeBSD and God= frey Tan PhD thesis at MIT.
>
> http://nms.csail.mit.edu/projects/apware/

Hmm, that link is not working for me right now; will try again later= .

> this work predates 802.11n and aggregation.

Yeah, I'm aware that there is a lot of stuff that predates 802.1= 1n. In
fact the article I linked (Kim et al) is the only one I've found that talks about 802.11n. We also had some people at my uni doing stuff with
802.11g.

> Ten years ago I played with SFQ and madwifi for 802.11g to get max-min=
> time fairness (and so proportional rate fairness) with excellent
> results. The hacking I made was based on using time quanta instead of<= br> > bytes. Which required me to get the current PHY rates (AP to all
> STAtions) and dynamically compute/update SFQ time quanta.

Do you happen to recall what precision you achieved or how much the<= br> precision was really important? Several papers seem to assume that very
high precision is not terribly important since it all evens out in the
end, and I can see how that could be true; but would like to have it
confirmed :)

what do you mean with prec= ision?
Do you mean in measuring the PHY rate?=C2=A0
Sho= rt term vs long term measurements? else?

The hard = part was adaptiveness. Correlation between the speed of the STA, the
<= div>PHY rate controller and quanta updates in SFQ.
Ideally we wer= e trying to approach something like=C2=A0
downlink channel schedu= ling in HSDPA where you have slotted time TX
and polling. A slot = in HSDPA (but also LTE) is a burst =C2=A0of fixed time size of several pack= ets.
Similar to what you want to achieve in your email point 1.
in HSDPA/LTE you have UEs feedback every ms in a side channel. So = rate adaptation
is a lot simpler.

As a s= ide note,
there are several differences in aggregates in 802.11n = and HSDPA/LTE
as in the latter the scheduler can send an aggregat= e containing packets using different modulation/coding schemes to reach dif= ferent stations with a single aggregate transmission.=C2=A0
For t= he records, this feature was rejected in the 802.11n amendement but discuss= ed =C2=A0by the group as it makes the chip more expensive.=C2=A0
=

=C2=A0

> It's surprising that 802.11 standard never considered time fairnes= s in
> the EDCF. A reason might be the time fairness might be enforced using<= br> > the PCF.

Might be. Might also be that no one thought to measure for that? A l= ot
of vendors seem to only test single-station raw throughput...

Are you aware of any open source 802.11 stuff that uses PCF at all?

No. Sorry.
=C2=A0

> IMO, It's a very good topic.
> Thanks for bringing this up.

You're very welcome! ;)

-Toke

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