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

[clayton_taverni]

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.

[clayton_taverni]

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

[robert_lowe_722]

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. 

[clayton_taverni]

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?  

[robert_lowe_722]

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.