[SZ100] 5GHz Radio Channelization: Auto vs 80 vs 40 vs 20?

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I attended a very nice Ruckus class yesterday and learned that my 5GHz radio channelization should maybe be at 40 or even 20 instead of the default 80.  

So I go into my SZ100 controller and look at the Common Settings and see that the 5GHz channelization is set to Auto.

Confused, I look at a particular AP and see it's 5GHz channelization seems to have a default of 80 which I can override and set to Auto, 40 or 20.

Very confused now, I'm wondering what the Auto setting in Common Settings gives me?  Why the APs are showing a grayed out 80 instead of Auto?  And where would I set the channelization to 40 if I wanted to?

Thanks in advance.
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Clayton Tavernier

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Posted 5 months ago

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Gowtham Elamurugan

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Hello Clayton,

You can change the channelization at Configuration->AP->common settings. Here you have options to set it to 20/40/80/Auto for both radios separately. 

Thanks,
Gowtham
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Gowtham Elamurugan

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Hello Team,

I have the same doubt here.. I have changed the channelization from Auto to 40MHz for 5GHz radio and faced heavy client disconnection. We are having SZ100 running 3.4 and 17 R600 Accesspoints. Client loadbalancing also not happened. 
Once changed to "Auto" resolves all the issues.

Somebody give an answer to the question asked by Clayton would be a great help.

Thanks,
Gowtham
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Michael Brado, Official Rep

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With Auto setting, the default is 80MHz channelization, but can step down to support 40MHz or 20MHz only client connections.
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Clayton Tavernier

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Understood.  But what does Auto do?  I assume there's a difference between Auto and setting 80MHz manually.
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Gowtham Elamurugan

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I have set it to 40MHz manually for 5GHz and felt heavy client disconnection in a high density environment with heavy interference. New client's were not able to join in the WLAN. Any specific reasons??
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Clayton Tavernier

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I'm not with Ruckus Support but 40MHz channels aren't as powerful as 80MHz channels.  Using 40MHz will give you roughly twice the number of clear channels as 80MHz but at half the strength.

If you have heavy interference, you either need more APs or to go back to 80MHz.

Again, not Ruckus Support.
(Edited)
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Clayton Tavernier

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Clayton Tavernier

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Robert Lowe

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Its actually the opposite, the shorter the channel width the more powerful the signal. Maybe you are confusing power and throughput? When choosing a channel width you also have to consider density, CCI and client types. Its important to note that Ruckus 802.11AC AP's will ALWAYS default to 80MHz channels. IME there is no point using the auto feature other than convenience of not changing as ive never seen an Ruckus AC AP choose anything other than 80MHz. There is a couple of reasons for this but the main one is throughput. Im positive the software makes the decision that because with 80MHz channels the throughput will be higher on average than 20 or 40MHz even if this causes CCI so it chooses that.

If you experience lots of client disconnects at 40MHz then there could be a number of issues for that, one could be a bug, did you try going down to 20? Another could be the channel that was chosen, was it the same centre frequency as when it was 80MHz? 
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Clayton Tavernier

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Thanks for the reply.  Am I at least correct in saying that in a denser environment, 40 is better than 80?
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Robert Lowe

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Yes you are. In a true dense environment you should be looking at using 20MHz channels as you need the spacial reuse more than the high throughput. Remember, 1 AP on ch 40 @ 80MHz can only server 1 client at a time. 4 AP's on 20MHz channels can server 4 clients at a time. 
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Clayton Tavernier

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Remember, 1 AP on ch 40 @ 80MHz can only server 1 client at a time. 4 AP's on 20MHz channels can server 4 clients at a time. 
Sorry, I was with you up until this one.

So how do you tell whether you have a 80MHz capable environment  vs 40MHz or 20MHz?  Is it just reported disconnections?  
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Robert Lowe

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You always have an 80MHz capable environment if you have 80MHz capable AP's. The issue is available airtime on any given channel. Don't forget 80MHz capable AP's are backwards compatible with 40 & 20MHz capable clients. 

There is a limited number of 20MHz channels available for use by law (defined by FCC/ETSI etc depending on your location) If you use 80MHz channels on your AP's you are effectively using 4 20MHz channels bonded together. This is fine in clean environments but where you have lots of 5GHz AP's this can mean AP's using the same channel as each other. This is know as co-channel interference. If a client hears another client transmitting on the same channel as they are using they will wait until the channel is clear before trying to transmit. This causes congestion and delay and effectively slows the network down.