DCA Channel Width Best (what is best according to the algorithm)

[emily00001]

I run a 2504 with a mix of 15 2702i and 2802i APs (10-20 meters apart) with software 8.3.104.61 (I know the number is odd, a Cisco contact provided it). They are used in a fairly densely packed office with a peak count of clients reaching to around 300 but they are not evenly divided and some APs might peak at 40 clients.

I have changed the channel width setting under 5 GHz DCA to Best and I ended up getting 80 % 80 MHz channels (the rest run 40 MHz). What exactly is considered by the channel width algorithm. I would consider the environment fairly high noise as it's a floor in an office building in a central part of town (hundreds of rogues detected) and from most literature I've found that the recommended width is 20 MHz in this type of setting.

I haven't really received any negative user feedback yet but it's only been running for two days this way.

What exactly does the best channel width algorithm take into account?

[Scott Fella]

In my opinion you really need to look at the channel utilization in your office. If it's high, then reduce he channel width.  In many of our high density sites, we still use 20mhz or 40mhz but never a mix and match. You must have the DCA set to "Best".  

As far as client per AP. Roaming is a decision on he client side. You can play around with setting max/min TX power and disabling data rates to create a coverage you desire.

-Scott 

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[Scott Fella]

I'm not a fan of custom code either:)  You might be running the beta because there are many issues with the x802 series AP's. 

-Scott 

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[emily00001]

Oh well, I'll probably do away with the Best Practice suggestion for "Best" channel width. I was expecting channel width increasing after office hours to see an extra boost in performance but that doesn't seem to be how it's tuned.

I never really got tried changing the data rates but maybe that's worth learning more about.

Thanks for the advice!

[Scott Fella]

The reason I don't or prefer using "Best" is because you don't know if client devices will prefer 40mhz or 80mhz or 160mhz over the lower bonded channels.  This would mean that if clients do prefer the higher bonded, that your client to AP distribution would skewed.  That is why I prefer that all AP's use the same channel width so that I don't have to worry about oversubscribed AP's if that makes sense.  Data rates is important to good RF health. If you ever have user say, "why is my signal low when I'm right under an AP", well it's be cause you are allowing the lower data rates.  Clients again make the roaming decision, but you have clients that will stick to an AP because the signal/SNR is still within the range.  You remove lower rates to reduce the coverage, making the client device roam to another AP.

-Scott 

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[lmaccaro]

You are getting wider channels in a high noise environment because the faster the clients transmit, the faster they free up airtime for others to transmit and thus reduce the overall noise.

Think of 80mhz channels like you are applying a .zip algorithm to all the clients that can support it.  If you have 10 clients all trying to upload 1gb, but you turned on 80mhz and 7 of them got their 1gb file zipped down to 300mb, well.. that's a lot easier on the network.