AP High Utilization - Tx Mgmt Frames High

[Najib Akbari]

Hi, I have sent this to TAC and the response was unable to pin point the issue and difficult to analyze it and asked me to run iPerf which I think it has nothing to do with this issue. I have given them the whole details though!

So I post it here and appreciate you guys can take a look and possibly assist with it:

Env: C9800 17.9.5  - AP 9164I

I have an AP showing High Utilization sometimes and that causes wireless client to experience very low RSSI and performance even though the client is not more than 10 feet away and not many clients. I have tshoot this and I need your help for further tshoot. here is what I have done - there are neighboring APs and the channels are different and far in my understanding: Nearby APs :

AP a00XXXXX slot 1 : -70 dBm on (116, 40 MHz) 

AP a00f.3xxxxx slot 1 : -84 dBm on (136, 40 MHz)

AP 345dxxxxxf slot 1 : -85 dBm on (100, 40 MHz) 

AP a00f.xXXXXX slot 1 : -90 dBm on (116, 40 MHz)  -

diged into DNAC analytics and realized the time user experiences wireless drop and bad performance DNAC reported high channel utilization on AP and poor RSSI on wireless client ( see attached)

• DNAC shows poor RSSI ~40% of time for the client even though the AP is close
• Then I checked AP DNAC analytics and WLC logs and noticed whenever the user experiences bad network the AP shows high utilization 70-80% which made me think it should be the root cause of the issue
• The high CU could be for many reason and mainly interference, but the user is connecting on 5Ghz channel and I could not find a significant interference on that radio nor channel overlap.
• So then realized the Hi CU is reporting for Tx rate and on that refers to Tx management frames is occupying high BW

As of the moment I think its high channel utilization causing this issue and according to DNAC it is mainly TX management data. but these are all my analysis and finding, not sure about the next step?!

[Flavio Miranda]

@Najib Akbari 

 High channel utilization is the number one wifi problem but it does not cause change on RSSI. RSSI will change due  distance or obscule. 

  I have two question: How many clients per AP do you have and how many SSID per Access Point?

[Najib Akbari]

average clients per AP is 10 but on this AP usually does not go higher than 5 clients. 4X Active SSID on all APs

[Leo Laohoo]

What country is this? 

Is there an airport nearby? 

Those affected channels are in UNII-2e and very close to known weather radar channels.

First things first, what is the business case for using UNII-2e channels?  Next, try 20 Mhz.  

[Najib Akbari]

US - Airport 15 Miles Away.

channel set to auto and currently the AP is on channel 56. the RRM DCA settings is here, which a while ago I set it based on some references got from some verified CCIE wireless holders, I personally am not expert on this, and I believe there is not business requirements per se to pick UNII-2e. I will appreciate if you can elaborate on the tech aspects of topic and may advise on my setings:

[Leo Laohoo · Accepted solution]

I strongly recommend someone review the channels selected/picked because they are so wrong in so many places.  

For North America, UNII-1 channels are 36, 40, 44 and 48.  UNII-2 channels are 52, 56, 60, & 64.  UNII-2e are 100, 104, 108 112, 116, 120, 124, 128, 132, 136, 140 & 144.  UNII-3 are 149, 159, 157 & 161.  In some cases, channel 165 can be used. 

Traditionally, it is highly recommended to use UNII-1, UNII-2 and UNII-3 channels and best avoid UNII-2e as a whole. 

In the screenshot provided, someone has completely gone topsy-turvey and disabled UNII-1 and UNII-3 but enabled every channels in UNII-2 and UNII-2e, particularly the bad ones!

[Najib Akbari]

Thanks so much for the details. I m the one to be blamed for not doing a proper research on this before apply!

I will make sure to make the necessary changes, but before that can you please elaborate a bit more on this ? some theory and for example so since i used DFS channels then that can be the root of the issue im reporting? also we have some but not alot of typical wireless routers tplink netgear and is that something to be considered when check marking channels in DCA 5G? I read somewhere those WRouters use UNII-I. basically for an environment with 2.4, 5G and light load 6e, with my explanation consideration still you recomment the same as your previous comment on channels selection ? thnx

[Leo Laohoo]

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@Najib Akbari wrote:
some theory and for example so since i used DFS channels then that can be the root of the issue im reporting

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Strong possibility, yes.  

If the wireless clients are connected to DFS channels and then, say, a weather radar is pointing to the direction of the APs, the wireless client will get kicked out and re-join the WLAN.  And everyone knows how "sensitive" people can get every time their wireless client switches channels!

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@Najib Akbari wrote:
also we have some but not alot of typical wireless routers tplink netgear and is that something to be considered when check marking channels in DCA 5G

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Not going to comment on what other manufacturers have in place, however, smart money is DFS channels are disabled by default.  If someone has turned them on, then it's YOYO (and pass the popcorn!).

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@Najib Akbari wrote:
I read somewhere those WRouters use UNII-I. basically for an environment with 2.4, 5G and light load 6e, with my explanation consideration still you recomment the same as your previous comment on channels selection ? thnx

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1.  Read this:  Cisco Wireless IP Phone 8821 and 8821-EX Deployment Guide.  About >70% of this document talks about how to tune the WLAN.  Download the PDF.  Keep a copy but, most importantly, read it. 

2.  Understand what is the WORST wireless client in your environment and work around that.  For example, our worse wireless client are ASCOM i62 WLAN handsets.  One of the "demands" is 20 Mhz channel width and no more than 8 channels.  So we were forced to only use UNII-1 and UNII-3 in places where these handsets are employed.  However, in places where these handsets will not be used we have enabled UNII-1, UNII-2 and UNII-3.   UNII-2e is disabled.  

[Najib Akbari]

Thank you do very much! live and learn! Appreciate your time and support on this! 

I have applied your recommended settings on all APs last night and now generally seeing less HC utilization, So I considered it resolved. but for this particular wireless client with this AP, even though the AP looks normal and not many clients, this clients shows DNAC poor RSSI, the laptop is old, I re-terminated the patch cord on the AP and it is normal for now but this poor RSSI reported by DNAC bugs me, well certainly its different issue to look into BUT most certainly with your help the main issue of High CU is resolved and Thank you!  

[Leo Laohoo]

Channel Width is "Best (DBS)"?

Don't use this option.   Set it to 40 Mhz but never use "Best".

[Najib Akbari]

The one below it “dynamic BW MAX..” set to 40, that would not do it?

[Leo Laohoo]

Even though the one below is set to 40 Mhz, don't set the Channel Width to "Best".

[Najib Akbari]

done.  Thanks!

[Najib Akbari]

Stupid Question, a CoWorker checked the AP physical port to the switch and said it could be the link as it might be a bit over 100M, even if thats the case is that something to correlate to the issue I described here?

[Leo Laohoo]

100 Mbps link has nothing related-to or would cause co-channel interference.