Initial automatic channel selection implementation

Luis R. Rodriguez mcgrof at
Wed May 25 15:24:23 EDT 2011

On Wed, May 25, 2011 at 12:20 PM, Felix Fietkau <nbd at> wrote:
> On 2011-05-25 5:01 PM, Luis R. Rodriguez wrote:
>> On Wed, May 25, 2011 at 7:45 AM, Helmut Schaa
>> <helmut.schaa at>  wrote:
>>>  On Wed, May 25, 2011 at 4:37 PM, Luis R. Rodriguez<mcgrof at>
>>>  wrote:
>>>>  On Wed, May 25, 2011 at 5:19 AM, Helmut Schaa
>>>>  <helmut.schaa at>  wrote:
>>>>>  On Wed, May 25, 2011 at 12:54 AM, Luis R. Rodriguez<mcgrof at>
>>>>>  wrote:
>>>>>>  Yes, thanks this is a lot of work already done. Now we just need a
>>>>>>  basic algorithm to parse this, quantify how ideal this channel is and
>>>>>>  then spit out a desired optimal channel.
>>>>>  That's what I've hacked some time ago (in form of the attached _ugly_
>>>>> shell
>>>>>  script that does auto channel selection with rt2x00, not sure if it
>>>>> works
>>>>>  correct with other drivers as the survey dump differs somehow between
>>>>>  rt2x00, ath5k and ath9k, and it only does channel 1-11):
>>>>>  - Iterate over all channels and stay on each channel for some time
>>>>  Nice, yeah I was thinking of using the offchannel operation if we want
>>>>  to spend more time there for inspection and if associated. For first
>>>>  iteration it should be possible to just move around. In fact for AP
>>>>  purposes I suppose one will want to just start AP mode ASAP and then
>>>>  later do offchannel operations to do the inspection on the ideal
>>>>  channel. Otherwise we sit there idle until we complete the Automatic
>>>>  Channel Selection thingy.
>>>  Correct, especially if we also consider 5Ghz channels. Offchannel
>>> operations
>>>  would be nice but how can we ensure AP mode while being offchannel?
>> Notification of absence.
>>>>>  - Store busy time stats for each channel
>>>>>  - Choose the channel with the lowest busy time (and on 2.4Ghz also
>>>>>   check the busy times on adjacent channels)
>>>>  So I was reviewing this -- if we are TX'ing or RX'ing it seems to me
>>>>  we should skip that time from the busy time, otherwise the "busy" time
>>>>  includes time we induced on TX'ing or RX'ing ourselves. So I was
>>>>  thinking of using the:
>>>>   (active time - rx time - tx time)  / busy time
>>>  Looks good ;) just one problem from a rt2x00 POV: We can't report rx/tx
>>> busy
>>>  time separately, we can only advice the hw to include or exclude rx/tx
>>> time
>>>  from the busy time statistics.
>> Doh, I see.. well in order for the above math to be useful we'd have
>> to be consistent across drivers. What is being done by rt2x00 right
>> now? If the later then the math would still work, otherwise then we'd
>> need to adjust.
> Excluding rx time isn't even a good idea, since it makes no distinction
> between local BSS or other activity in the area.

What if we do an offchannel operation?


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