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Subject: Re: mac80211_hwsim: multiple antennas
To:     Ramon Fontes <ramonreisfontes@gmail.com>,
        Johannes Berg <johannes@sipsolutions.net>
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From:   Benjamin Beichler <Benjamin.Beichler@uni-rostock.de>
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Date:   Fri, 23 Nov 2018 15:18:41 +0100
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I haven't used hwsim with hostapd yet, but I'm pretty sure, that it is
possible to change the beacon rate (as we changed them in 802.11s Mesh
Mode).

I'm think the problem here is, that you can't assign a HT rate for
beacons, because action/management frames are always sent with base-rate
or at least they need to be sent with legacy-rates in mixed mode.

I'm not sure, whether hwsim can use the "green-field" mode, in which
everything is sent with ht-rates, but most drivers for real devices do
not support green-field mode.

So the highest beacon rate seems to be 54.0 mbit/s.

Nonetheless, hwsim do not simulate the real timing behavior of this
rates. Since hostapd is only responsible for the association protocol
but not data transmission, it should not decrease the seen rates
extremely, but I have no numbers for it.
As more effort you use to simulated the on air behavior, you decrease
the throughput rates.

kind regards

Benjamin

Am 22.11.2018 um 13:18 schrieb Ramon Fontes:
> I've tested the same setup with adhoc and the throughput seems to be
> higher as expected. Thus, the problem comes up when I use hostapd.
>
> I noticed that the maximum supported rate by hostapd (legacy) is 54Mbps.
> Extended supported rates: 24.0 36.0 48.0 54.0
>
> Then I tried to modify mac80211=5Fhwsim in order to provide more rates
> and it didn't work:
> Extended supported rates: 24.0 36.0 48.0 54.0 54.0 54.0 54.0
>
> The maximum supported rate is always 54Mbps.
>
> Then I found the Beacon frame TX rate configuration from hostapd.conf.
> After trying to enable the beacon rate (e.g. beacon=5Frate=3Dht:1) I got
> the following msg:
> ap1-wlan1: interface state UNINITIALIZED->HT=5FSCAN
> Using interface ap1-wlan1 with hwaddr 02:00:00:00:02:00 and ssid "ssid-ap1"
> nl80211: Driver does not support setting Beacon frame rate (HT)
>
> and hostapd doesn't work.
>
> Could this problem be related to mac80211=5Fhwsim=3F
>
> Em qua, 21 de nov de 2018 =C3=A0s 10:09, Ramon Fontes
> <ramonreisfontes@gmail.com> escreveu:
>> Yes. I thought that it could be related to the number of antennas (or
>> something else) after seeing this result
>> (https://bobcopeland.com/blog/2014/09/wmediumd-speed-test/) provided
>> by wmediumd.
>> Em qua, 21 de nov de 2018 =C3=A0s 09:48, Johannes Berg
>> <johannes@sipsolutions.net> escreveu:
>>> On Wed, 2018-11-21 at 09:47 -0300, Ramon Fontes wrote:
>>>> Okay! Thanks a lot.
>>>>
>>>> Indeed, the maximum throughput when using only hwsim is in the order of G=
bp/s.
>>> So I guess the question is where it's going wrong - is it the wmediumd
>>> overhead (netlink), some air simulation in wmediumd, etc.
>>>
>>> johannes
>>>

-- 
M.Sc. Benjamin Beichler

Universit=C3=A4t Rostock, Fakult=C3=A4t f=C3=BCr Informatik und Elektrotechnik
Institut f=C3=BCr Angewandte Mikroelektronik und Datentechnik

University of Rostock, Department of CS and EE
Institute of Applied Microelectronics and CE

Richard-Wagner-Stra=C3=9Fe 31
18119 Rostock
Deutschland/Germany

phone: +49 (0) 381 498 - 7278
email: Benjamin.Beichler@uni-rostock.de
www: http://www.imd.uni-rostock.de/