DFS channels unavailble due to RADAR interferance, best way to use NON DFS channels

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We have an extreme wireless configuration (5210 controller and  ap 3805 ) and had been using the additional DFS channels.
These Ap's are giving us alarms about RADAR.. Ok we are near an local Airport so I can understand this . So my question is , now we do not have the 4 additional channels , what is the best way to use the 4 available non DFS Channels, small cells ? still using the auto channel selection with low power ?

We have just checked the internet and can see that Weather Radar works between 4 -8GHz.. working with our 5Ghz for Wireless..

Any comments and advice , would be apprecieted
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Rod Robertson

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Posted 2 years ago

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Douglas Novell, Employee

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Hi Rod,

Sites utilizing 5ghz should have a Site Survey performed for optimal coverage based on data requirements. This is imperative. 

With that said, DFS channels should be removed as available channels to avoid client disruption.

Suggested 5ghz channel list for US country code with DFS (UNII2) channels removed.

channel-list 5GHz 36,40,44,48,149,153,157,161,165
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Ostrovsky, Yury, Employee

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Hello Rod . The 3805 AP should support about 10 DFS channels . Do you see the DFS events on all those channels? 
If you have ExtremeManagement , you can set email notification to see and track the DFS events , so it will be easier to make a decision later - e.g. exclude those DFS channels which giving problem. 
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Rod Robertson

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My customer has now set up that the channel change creates an alarm , hopefully we will be able to create a list of affected AP's and where they are located , we have 800+ AP currently on the system ..
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Ondrej Lepa, Employee

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Hi Rod,

First thing is - do you need 40 / 80 MHz wide channels or is it more about having more separate channels to be used?

Second - DFS is based on country regulations so take a look where / if there is a gap where DFS is not required.

Third - DFS is not related to AP coverage cells or radio Tx power. Once AP senses RADAR signal, it just have to act.

See below part of CWAP study guide
When a radar blast is detected, all stations must leave the affected frequency. This capability is a part of Dynamic Frequency Selection (DFS). In countries where compliance with 802.11h is implemented, stations operating on UNII-2 and UNII-2 extended bands must also comply with transmit power regulations. This is called Transmit Power Control (TPC).
I would recommend to tweak supported channel plan to use rather non-required channels (based on country code) if possible. Otherwise I am afraid you'll need to accept the DFS at your location.

Let me know if you have any further questions.

Regards,
Ondrej
(Edited)
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Rod Robertson

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Hi

Basically its about have more channels that we can use , if the DFS channels are getting scanned , then basically we need to use only non DFS channels , which then to get coverage etc , we will need to create smaller cells , to meet our capacity requirements. 
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Ostrovsky, Yury, Employee

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Some time ago I made a small video regarding DFS and how we can prepare our network to carefully use it . If you have time please take a look here https://youtu.be/9DG0Q1CRHeQ . Any comment appreciated. 
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Rod Robertson

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MAny thanks for your excellent responses.

This is what I have sent to my collegues for discussion.

 Wow what a subject..

 

Basically what happens , if the AP configured to use DFS channels sees a Weather Radar or other military type frequencies it automatically moves to a none DFS channel , which then basically messes up the wireless cell structure as then you could have 2 or more AP’s in the same location of the same frequency  , causing cell interference and general rubbish wifi performance.

 

There is also another issue with using DFS and that is,  does the “end user equipment”( Phones/Mac/Tablets ) support these upper channels , again the only way to see  this would be to somehow monitor the connections per AP .. those on the higher channels , have less /same / more connections than your average none DFS AP .

 

Looking at the Weather Radar, we discussed a few options:

 

We could be more selective in how we allocate 5Ghz channels allowing the external accessible  AP’s ie those that would “see” the weather radar scans  to be configured as NON DFS , and as we are aware 5Ghz does not penetrate too far into the building through walls , use DFS channels on these AP’s.

 

From what I have read “weather radar “ uses channels 116-132 , therefore these should be removed from our configuration ..

 

Another option is to give the DFS configured AP’s a predetermined NON DFS channel to switch to in the event of a  weather radar scan, though again here we are basically going back to static configuration of AP’s and also knowing the surrounding allocated channels.

 

So there you go , the start of an interesting discussion.
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Rod Robertson

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