dealing with excessive ap channel utilization

[DAVID]

I have a Cisco 5520 running 8.2.x code for Cisco 3700i access points located in retail locations across the US.  These location can range from large shopping malls, strip malls, to stand-alone locations.  Most of these retail locations because of size only require the need for 1 access point while some retail locations do have 2 and even three access points.

My question is two fold.  What is the minimum number of AP's in a given area that RRM is used to allow the controller to automatically adjust the ap's channel and power based on environmental and adjacent access points?

I am finding for some locations that channels 1, 6, and 11 are so full of interference and channel utilization that I have to manually change to completely different channels.

How can I get PI to alert me whenever a channel on the 2.4GHZ reaches a threshold of say 60% or greater?

[Scott Fella]

RRM requires at least three AP’s to hear each other from the controller that is the RF Group Master. Having one or two AP’s per store will not make them participate in RRM but you can still enable CleanAir to make decisions. The 2.4ghz is so utilized everywhere that it’s better to focus on the 5ghz and try to only make the 2.4ghz at least usable. I have just ran reports on PI for CU or you can review the RF dashboard that will show current CU. It’s nice and simple. I wouldn’t worry more much about manually changing channels in the 2.4ghz because it’s over 60%. I had a site in a shared tenant building in London which the 2.4ghz was around 75% after hours. We tested a Skype call just for kicks and the user didn’t notice any issues. Majority of the devices are connecting to the 5ghz with only around <10% connecting on the 2.4ghz. 1, 6 and 11 being used everywhere in a mall doesn’t leave you with much choice. Enable CleanAir and allow it to do the work. Power will always be the highest which would be good for you, but unless your in a strip mall where not all stores have wireless, I don’t know what free channels you would have. CU goes up with client count and traffic so this can change dramatically. Find sites that have high CU and have users provide feedback when it high and when it’s not and see if there is any significant difference. They might just complain because it’s slower than what they are use to at home.
Just my opinion:)

[DAVID]

Does DCA, dynamic channel assignment depend on a minimum of 3 access points as well? I have to keep the 2.4 because of the Motorola scanners and zebra wireless printers.

[Scott Fella]

DCA is what channels you allow that is valid for that country. This has nothing to do with RRM per say.

[Scott Fella]

So since you have 2.4ghz devices, the best thing to do is at least keep the power at max and only have 1, 6, 11 defined in DCA. Don’t use any other channels.

[DAVID]

We do have those channels in DCA on the controller but I have so many locations with just 1 or 2 access points where ch. 1, 6, and 11  that I can find to be over utilized by greater than 60%  that I have no choice but to manually change the channel to something completely different and then the clients are fine.

So let me see if I have this correct.  If I have 3 or more 3702i access points I should be ok with the DCA and RRM, and cleanair doing their jobs.  However, if I have less than 3 than all I can really hope for is that Clean Air will automatically adjust the channels to less utilized ones between 1,6, and 11?

At the end of it all I can't turn off the 2.4 because of the 2.4 bar code scanners in the store that are limited to that.  Either way with a store with only 1 access point even a 3800 will not make any difference.

[Scott Fella]

Just to be clear, you should not use any other channel than 1, 6, 11. Channel 1 bleeds into channel 2 and 3. Channel 6 bleeds into 4, 5, 7, and 8. Channel 11 bleeds into 9 and 10. So if everyone else is using channel 1, 6, 11, then all other channels are affected also.
If you have enough data that shows if you change an AP to channel 3 and the utilization is lower than 60% then out those channels in DCA. DCA are the channels you want to use.
It doesn’t matter if you have 20 AP’s or just 3. The 2.4ghz is over utilized and there is nothing you can do about that. RRM will just choose a channel that is the best even if it’s 90% utilized. You seem to be looking for that magic fix, which there isn’t for 2.4ghz. This is the same issue for other vendors also not just Cisco. The other tenants in the mall are affected the same way as you.
If you want to see less CU from the AP’s point of view then set your RX-SOP to high. Here is a link on RX-SOP:
https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-0/hdx_final/b_hdx_dg_final/high_density_experience_features_added_in_release_8_0.html
Just remember this is for the AP’s to not listen to anything below a certain RSSI. This doesn’t mean on the end devices that CU is low.
We have sites around the globe that utilization is high on the 2.4ghz after hours with no clients in the office. We let RRM make the determination but at times it can hit 80% or more. Other tenants also use vendors that chooses the best channel so this changes dynamically but can’t lower CU that is already out there.
Find a site that is always high and put three AP’s out there. See if RRM works for you or not. This way you have an idea if you should just have three AP’s per site or if this doesn’t help you at all.

[DAVID]

First of all thanks you for all this valuable information.  The fact that I am restricted to the 2.4 is due to the bar-code scanners at the stores and that 90% the stores(500+) are only running 1 3700i AP.  It seems at the end of the day there's little to nothing I can really do on the wireless side if the stores are limited to using bar-code scanners that will only operate at 2.4gHz

[Scott Fella]

David,

The only thing you can do is at least make sure he TX power is high and that you have enough coverage. Playing with data rates also helps with performance but it also depends on he scanners and printers to see if you can disable the lower rates or not. If you have one device that still uses 802.11b, then your limited to what the device you can do.

[Leo Laohoo]

The problem with CleanAir and APs like 2700/3700 and earlier is that CleanAir can identify the co-channel interference. The problem steps in with "what are you doing about it". With2.4Ghz the adjacent channels are so overcrowded that there's really no place to go. It's like trapped in an alley. If places where we got 3700, we've manually turned a lot of them OFF.
If you've got APs like 2800/3800 then it's good because CleanAir will actually be beneficial because CleanAir can turn off 2.4 Ghz and enable the micro 5.0 Ghz (along with the main 5.0 Ghz).

If you don't have clients using 2.4 Ghz, turn it off.  If you do, crank up Data Rates.  Start with disable 11 Mbps and below.  Set 12- and 24 Mbps to Mandatory and the rest are Supported.