RRM/DCA Global vs Radio Profile Settings

stelker77 · ‎09-24-2020

Hey all,

I am working with a Cisco 8540 Wireless Controller. I am using radio profiles to roll out settings changes to AP groups (Wireless > RF Profiles, applied at WLANs > Advanced > AP Groups). I have two DCA options in the Radio Profile > RRM tab. The two options are "Avoid Foreign AP interference" and "Channel Width". Can anyone confirm if the rest of the global DCA options (the options at Wireless > 802.11a/n/ac or 802.11b/g/n > DCA) still apply to AP groups w/ this radio profile other than these two? Or does using Radio Profiles nullify the global DCA options for the AP groups with these radio profiles assigned?

Also, any help understanding the following output would be much appreciated:

(Cisco Controller) >show ap auto-rf 802.11b W334-B10

[...some output omitted for brevity...]

Nearby APs
AP 18:80:90:84:dc:d0 slot 0.................. -73 dBm on 1 20MHz (172.25.200.43) W334-B5
AP 18:80:90:a3:4a:f0 slot 0.................. -89 dBm on 6 20MHz (172.25.200.43) W334-FrontOffice1
AP 18:80:90:ab:45:10 slot 0.................. -78 dBm on 1 20MHz (172.25.200.43) W334-A12
AP 18:80:90:ab:4a:60 slot 0.................. -84 dBm on 1 20MHz (172.25.200.43) W334-B2
AP 18:80:90:ab:51:e0 slot 0.................. -87 dBm on 1 20MHz (172.25.200.43) W334-FrontOffice2
AP 18:80:90:b5:0f:f0 slot 0.................. -93 dBm on 1 20MHz (172.25.200.43) W334-A4
Radar Information
Channel Assignment Information
Current Channel Average Energy............... -77 dBm
Previous Channel Average Energy.............. -77 dBm
Channel Change Count......................... 0
Last Channel Change Time..................... Tue Sep 22 19:08:09 2020
Last neighbor CHD Event...................... 73980 Seconds Ago
Recommended Best Channel..................... 1
RF Parameter Recommendations
Power Level.................................. 4

[...some output omitted for brevity...]

Why wouldn't this radio select channel 11, which is completely clear from its perspective? I am having similar behavior on the 5GHz spectrum, where there are channels that are completely clear, and available for selection from DCA's channel list (like channel 52, 157, etc.) and the AP will instead select a channel that has a relatively high RSSI from a neighbor (in the 70's). Do I need to change the global DCA Channel Sensitivity from Medium to High? We do have Channel Assignment Method set to Automatic and it is running every 10 minutes. I would love for AP's to be as avoidant of co-channel interference as possible.

Thanks for any advice, insight, comments or good jokes

patoberli · ‎09-28-2020

This is a fairly complicated theory here. Full documentation: https://www.cisco.com/c/en/us/td/docs/wireless/controller/technotes/8-1/mobility_express/b_RRM_White_Paper/b_RRM_White_Paper_chapter_00.html

To start with, why does the WLC not select channel 11. The default RRM / DCA settings define something like this (I don't fully remember the exact values and I think those are the default values): if three other neighbor APs on the same channel have more than -72 dBm, then use another channel. If it's less than three, then keep the same channel.

That is why your AP is staying on channel 1, the others have a weak enough signal to not disturb this AP to much.

To your first question, I'm not entirely sure, but I think the AP Group settings take priority over the global settings. So I would configure your preferences there.