Radio Profile - channel selection auto - neighbor APs on same channel & running at Max power allowed.

[w1f1n00b]

I’ve been seeing many instances where APs are on the same channel as their neighboring AP with RSSI in the 60s or 70s. I’m looking for steps to take to prevent this that don’t require manual channel plans, as I have too many APs to manage in that manner (wish this wasn’t the case).

In this one example I’m trying to figure out why the two radios are showing drastically different channel costs. full disclosure, not really sure what these numbers mean or how they’re calculated so any info or resources are greatly appreciated.

Also of note, these Radio Profiles are set to auto power selection with max power of 14dB. There are 50+ APs at the site (apx every other room), yet every AP is running at power 14. none have adjusted power down at all. Is this typical? My understanding is that even if Co-channel and adjacent channel interference are minimized, RF should still be kept to minimum power necessary to avoid general interference.

[w1f1n00b]

The problem I’m having is that APs don’t appear to respect the DCS settings. I tested this, and GTAC confirmed, that even with DCS disabled, APs will still change channels based on interference. This is why they recommended the route of manually adjusting radio powers etc. (however I think there is more going on than that)

I set up three test sites

site 1-DCS OFF - still seeing channel changes

site 2- DCS ON, Interference Threshold OFF -still seeing channel changes outside of maintenance window (which it should only due based on interference, which based on policy wasn’t allowed)

site 3- DCS ON, Interference Threshold ON - many channel changes UNTIL… I applied a beta firmware on 11/5 due to an open ticket regarding high crc errors, and since then all channel changes have been inside the scheduled maintenance window.

So. their might be light at the end of this tunnel. I just wish there was better documentation of ongoing issues so I don’t have to beat the bushes trying to figure this stuff out.

 @Sam Pirok do you have any info regarding acsp, background scans, DCS, and DFS channels? I’d love to get some clarification since I was told by GTAC while on the phone with my SE working on a ticket, that APs will not perform background scanning while using DFS channels. 

[jose_gonzalez]

Don’t allow APs to switch channels if thresholds exceed x percentage in the radio profile.  It causes more problems than it solves in dense areas because all channels may experience high interference, and it will switch, switch and switch.  Only permit channel switching during a allowed time range or with 0 clients connected.  Yes when using DFS channels it can occasionally experience a channel change if it detects radar, at that there is even a protocol to notify the clients of the change.  Especially with the dual 5G you have going, you really need to enable DFS.  In my professional opinion your making things harder for yourself and your users.

[w1f1n00b]

I’ve never used SDR. I’m running a device template configured for dual 5GHz at sites that no longer need 2.4GHz support where AP250 & AP550s have been installed.

I’m still skeptical about MU-MIMO. I’ve heard time and time again that it was mostly a marketing gimmick as far as how good it functions in the real world. Maybe it’s an Aerohive specific issue/firmware problem. I don’t see how such an important feature would be disabled by default and recommend against (I’ve heard it directly from the mouth of David Coleman). But again I’m open to the possibility. This is something I may need to do further testing on.

Regarding clients being connected, I really started playing with this after noticing hundreds of channel change events at most sites throughout the coarse of the day (I’ve since reverted my templates to allow bg scans while clients are connected). I played around with different settings and determined that even with DCS (dynamic channel selection) turned off, APs were still changing channel.  In the one instance where I worked with GTAC their recommendation was to manually adjust radio powers to reduce interference. We tested in a building with an AP in every room. Radio profile was set to max power 16 (dual 5ghz). All APs were running at power 16. We worked for a few weeks making different changes and adjustments, and ended up with power set manually to 2dB (down from 16, thats a huge difference). At that point the channel changes become mostly non-existent. However I don’t have the time to support manual configs on thousands of APs, and currently rely heavily on auto radio settings which is why I’m here trying to determine what is acceptable.

I feel like I’m between a rock and a hard place. In some cases I’m being told the auto channel power settings are fine, and in others I’m being told they’re the cause of channel changes outside of maintenance windows due to high interference (sometimes dozens per AP per day). All this on top of often finding APs on the same channels as neighbors, almost never seeing 5GHz radios pull their power down, and ongoing false high-interference alarms really just leaves me feeling skeptical.

[jose_gonzalez]

I noticed in your screenshots that both radios are in 5ghz mode.  I discovered some type of bug in the AP410c 10.2r2 code that prevents the SDR profiles from working correctly and results in radio0 always choosing 5g.  If you are running 10.2.2 go back to 10.1.6, or don’t use SDR profiles.  I opened a ticket about a month ago, with all the GTAC data they needed to validate wrapped, bow tied, they are still working on validation.  They don’t have the h/w to test with.

You can mitigate CVE-2020-16152 with 10.1.6 with CLI supplicant:

no system web-server hive-UI enable

[jose_gonzalez]

The radio1 interface has to perform radar background scans to use DFS channels, that’s the whole thing about DFS.  ACSP does scan and evaluate the DFS channels if enabled when in channel selection mode.  GTAC gets it wrong from time to time.  A/C is all about MU-MIMO, if you want your AC / AX clients to experience the performance they were designed for, enable it on radio1.

If your in a dense environment I would consider allowing the channel switch at a particular time range, I charge carts too and it’s no big deal for me, the clients would connect to a neighboring AP.  APs will choose a random time within the time range to channel scan.   If you really can’t then make the window scan range as close to 24 hours as possible when 0 clients are connected.  This AP is 20mhz, make sure all APs in dense areas are at the bandwidth.

I also can’t believe that ACSP would blindly select a channel on startup without performing channel scan first.  It should perform a normal channel then based on lowest channel cost select a channel, selecting the last known channel in cases of ties.

Did you know you can force APs into ACSP channel selection mode in the CLI?

ap# show int wifi1 | inc mhz
Freq(Chan)=5180Mhz(36); EIRP power=25.77dBm; Diversity=disabled;
Channel width=20Mhz; HT-protection=Green field; Deny client=none;

ap# int wifi1 radio channel 36
ap# int wifi1 radio channel auto