3802i dual 5 GHz or 40 MHz wide channel

[tiluna]

Hi,

I have an area that is experiencing high channel utilization on an AP (3802) on 5 GHz.  I think it's being caused by the high amount of traffic and clients on the AP/channel. .  The AP is currently set for 20 MHz wide channel.  Would it make more sense to increase the channel width to 40 MHz or manually disable the 2.4 GHz radio and make it a dual 5 GHz radio?

I don't have FRA enabled.

[Flavio Miranda]

Hi @tiluna 

  What do you call high channel utilization? above 80%?   Increase the channel width will not help, actually is the opposite. If you change the channel width to 40Mhz you will have less channel available which will increase the number of Access Points using the same channel thus increasing channel utilization.

  If you are facing high channel utilization with 20Mhz in 5.0Ghz you have some big problem happening. Increate the number of radios by disabling 2.4Ghz can help but it will also mean more radios disputing 5.0Ghz frequency thus increasing channel utilization.

  First thing would be measure how many users you have per 5.0Ghz radios.  This can be the offender.  Second, see what is causing retransmition (the high channel utilization or something else and then causing high channel utilization). Lots of clients sending small packets all the time can cause high channel utilization.

[Leo Laohoo]

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@tiluna wrote:
I have an area that is experiencing high channel utilization on an AP (3802) on 5 GHz.

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Find the source of the high channel utilization is the most important step.  

Making changes to the wireless LAN without first identifying the cause of the issue is like a doctor prescribing medication to a patient without medical diagnosis.  

[tiluna]

My mistake.  It looks like channel utilization sometimes peaks at 30% on the AP on 5 GHz, but retries are high at times for the clients.  The AP at times has about 25 clients on 5 GHz.  There aren't any other AP's on the same channel on 5 GHz.

[Flavio Miranda]

30% is ok for 25 clients and do not represent a huge problem.

 Retries  is normal in a half duplex network like wifi the question is how much it is impacting user performance

[Leo Laohoo]

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@tiluna wrote:
It looks like channel utilization sometimes peaks at 30% on the AP on 5 GHz, but retries are high at times for the clients.  

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But is that reading taken in "real time" or in a 24-hour time frame? 

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@tiluna wrote:
The AP at times has about 25 clients on 5 GHz.

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Even with just 1 Gbps uplink, 25 x APs on a 3802 is nothing. 

I have 3700 with >90 daily users and no complaints.  

[ammahend]

all good suggestions.

not a bad idea to keep AP channels 40 MHz apart (manual tuning needed) , if they are in same room, disabing 2.4 is ok.  Enable client load balancing if you are not using time sensitive applications. 

[Rich R]

And what nobody else asked so far - what model of WLC and what software version?

Note there have been a number of bugs for channel utilisation - most recently:
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwa31596
Also these (and a few other older ones):
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvt51979
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvz94552