[ath9k-devel] Disable b mode and prioritize ack on 5 GHz

[ath9k-devel] Disable b mode and prioritize ack on 5 GHz

[Alexander Szlezak]

Dear Ath9k developers,

We've been using Ath9k now with good success and I want to thank you for
the awesome work.

Mostly we didn't have a large number of users per ap but now we do expect
that in an upcoming project. I've done some performance testing comparing
ubnt unified stock drivers to Ath9k recent trunk on openwrt ad Ath9k had
around 5 to 10 MBit higher throughput with an atherosclerosis n client.

Now I am expecting a couple of hundred active devices in a room an I am
wondering what I could tune to optimize spectrum and airtime usage.

Approaches U have heard of are:

- kick clients with bad rssi after some time (hostapd)
- deactivate b modes (how can that be done didn't find settings for this)
- slow down 2.4ghz association with acks to lure 5ghz capable devices to
the available 5ghz aps
- increase dtim interintervals to reduce Beacon airtime usage

What is possible and can be recommended in a setup with 6 2.4ghz aps and 4
5ghz aps which I try to setup with minimum output power for spatial
separation

Thank you,
Alexander

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[ath9k-devel] Disable b mode and prioritize ack on 5 GHz

[Jouni Malinen]

On Wed, Sep 05, 2012 at 05:11:23PM +0200, Alexander Szlezak wrote:
>    - kick clients with bad rssi after some time (hostapd)
>    - deactivate b modes (how can that be done didn't find settings for this)
>    - slow down 2.4ghz association with acks to lure 5ghz capable devices to
>    the available 5ghz aps
>    - increase dtim interintervals to reduce Beacon airtime usage

You can two (2) and (4) with hostapd configuration (though, increases
DTIM period would not really have that noticeable differences; maybe you
were thinking of Beacon interval instead). (1) and (3) would require
changes to current implementation. There are various ways of trying to
encourage the station to another AP, but all these come at some risk of
interop issues since some stations simply don't like being told so in
vendor specific ways.. ;-)

>    What is possible and can be recommended in a setup with 6 2.4ghz aps and 4
>    5ghz aps which I try to setup with minimum output power for spatial
>    separation

Do you know what kind of station devices are going to be there? Do you
need to support 802.11b devices at all? Do you need any long range
connections to the these APs? If not, I would just disable lowest couple
of TX rates and potentially configure some channels to have HT-only
configuration if you expect to see relatively large percentage of HT
capable stations. Doing many of the more active load balancing tricks
will require code changes (likely in hostapd) (and experimentation to
verify it does not break deployed stations badly).

To prevent 802.11b stations from associating: add one of the OFDM rates
(say, 6 Mbps) into basic_rates parameter into hostapd.conf.

To allow only HT stations, add require_ht=1 into hostapd.conf.

-- 
Jouni Malinen                                            PGP id EFC895FA

[ath9k-devel] Disable b mode and prioritize ack on 5 GHz

[Alexander Szlezak]

Hi Jouni,

Thanks for your elaborate answer.

Am 06.09.2012 12:09, schrieb Jouni Malinen:
> On Wed, Sep 05, 2012 at 05:11:23PM +0200, Alexander Szlezak wrote:
>>     - kick clients with bad rssi after some time (hostapd)
>>     - deactivate b modes (how can that be done didn't find settings for this)
>>     - slow down 2.4ghz association with acks to lure 5ghz capable devices to
>>     the available 5ghz aps
>>     - increase dtim interintervals to reduce Beacon airtime usage
>
> You can two (2) and (4) with hostapd configuration (though, increases
> DTIM period would not really have that noticeable differences; maybe you
> were thinking of Beacon interval instead).

You're right, i meant Beacon interval. I thought longer beacon interval 
on 2.4 could lure dual frequency devices into 5ghz band too. Still have 
to test it.

  (1) and (3) would require
> changes to current implementation. There are various ways of trying to
> encourage the station to another AP, but all these come at some risk of
> interop issues since some stations simply don't like being told so in
> vendor specific ways.. ;-)

hm, those changes are probably out of scope for the project I'm planning 
considered the required testing.
>
>>     What is possible and can be recommended in a setup with 6 2.4ghz aps and 4
>>     5ghz aps which I try to setup with minimum output power for spatial
>>     separation
>
> Do you know what kind of station devices are going to be there? Do you
> need to support 802.11b devices at all?

Actually not. I suspect multiple devices per user and mostly mobile 
devices which usually have low b penetration (currently 54 % iphone 
which are g compatible) in our networks. I thought maybe i reserve one 
frequency for b devices with your proposed settings.

  Do you need any long range
> connections to the these APs?

no, absolutely not, just about 20 meters in radius

  If not, I would just disable lowest couple
> of TX rates and potentially configure some channels to have HT-only
> configuration if you expect to see relatively large percentage of HT
> capable stations.

yep sounds reasonable!

Doing many of the more active load balancing tricks
> will require code changes (likely in hostapd) (and experimentation to
> verify it does not break deployed stations badly).

I will first test the other options as we probably have not enough time 
to do radical changes.

> To prevent 802.11b stations from associating: add one of the OFDM rates
> (say, 6 Mbps) into basic_rates parameter into hostapd.conf.

Ok perfect. I'll try to have Ap's equipped with that setting except for 
one for the b clients and see if the properly find it.

> To allow only HT stations, add require_ht=1 into hostapd.conf.

I'll try to do the same as above and see if I get the right clients there.

best,
Alexander

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[ath9k-devel] Disable b mode and prioritize ack on 5 GHz

[Malinen, Jouni]

On 9/11/12 6:54 AM, "Alexander Szlezak" <alex@szlezak.com> wrote:

>You're right, i meant Beacon interval. I thought longer beacon interval
>on 2.4 could lure dual frequency devices into 5ghz band too. Still have
>to test it.

Many (most?) devices use active scanning on 2.4 GHz and as such, longer
Beacon interval may not have any effect on them finding the AP. If they
were using passive scanning, this could potentially have some change in
the behavior. Some networks use similar means by not sending all Probe
Response frames (which would affect active scanning) to stations that have
been seen on 5 GHz band. This would also be in the category of require
implementation changes in hostapd (and coordination among the APs to
figure out which STAs are 5 GHz capable since the Probe Request frame on
2.4 GHz band alone may not provide that information).

- Jouni