CT5508 - Channel width 40mhz connection drops

[bozo.bogd]

Hello,

I am having strange connection drops once I configure custom RF profile which is set to Channel Width 40Mhz and apply it to ap-group. Its not caused by long distance from access-point.

Goal is of this change is of course to increase throughput.

Same drops are happening if I hard-code it as global settings.

It affects all devices, new Apple Mac, phones, older devices as well.

Configuring channel-width to "Best" does even worse for overall Wi-Fi experience.

Once it's back to 20Mhz, default, everything goes back to normal.

Hardware

AIR-CT5508-K9

Operating System

Cisco WLC 8.3.150.0

All access-points are AIR-AP1832I-E-K9.

I ll add some screenshots of RF profile and best practice implemented.

Any suggestion or advices is highly appreciated.

Regards,

Bozo

[superego]

Might be possible due to DFS that client disconnect.

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvk79597

You can try upgrading your 5508 controller to Cisco's suggested version 8.5.171.0 ED

Check the release notes:

https://www.cisco.com/c/en/us/td/docs/wireless/controller/release/notes/crn85mr7.html#crn85mr7

Check  8.5.182.0 ED, it is newer.  See release notes:

https://www.cisco.com/c/en/us/td/docs/wireless/controller/release/notes/crn85mr8.html

[Arshad Safrulla]

First of all troubleshooting RF issues based on assumptions and adhoc changes will definitely not going to help. I would certainly recommend you to conduct a physical walkin survey with Ekahu sidekick or any other spectrum analyzer. This will give you visibility in to your RF environment as well as the AP positions.  Keeping that in mind below are some general recommendations which can help you to solve the issues, but not guaranteed. 

1. All the lower data rates. Solved: WLC Data Rates - Cisco Community

2. Upgrade the WLC to the latest recommended Aireos and the connecting clients to latest drivers Recommended AireOS Wireless LAN Controller Releases - Cisco

3. If you haven't done a survey stick to the lowest possible channel width. This will give you more channels to play with. (20Mhz is recommended since you dont have much RF visibilty)

4. Increase the DCA timers, dont use 10mins. Radio Resource Management White Paper - Dynamic Channel Assignment (DCA) [Cisco 5500 Series Wireless Controllers] - Cisco

5. Disable spectrum intelligence on the AP's. WLC version 8.6 Spectrum Intelligence on Cisco Wave 2 APs - Cisco

6. Enable band select, this will steer the clients to 5GHz. Load Balancing and Band Select on the Cisco Wireless LAN Controller - Cisco Community

7. Make sure that the clients are connecting to 5GHz. You can check from the client side as to which channel and also MCS rates negotiated. From WLC and AP side make sure that the 5GHz interface is enabled. (for Windows u can use netsh commands, for MAC How to See Your Current Wi-Fi Connection Speed in Mac OS X (howtogeek.com)

8. Make sure that you have configured the correct country code, dont enable multiple country codes. Configuring Country Codes on WLC | mrn-cciew (mrncciew.com)

9. 1832 is Wave 2, so it does support Uni2 extended and Uni3. So make use of all of them. If you see any DFS on certain channels exclude them from the RF profile. Radar Detection in Dynamic Frequency Selection (DFS) Channels - Cisco

[Rich R]

The wider your channel width the higher your chances of false radar detection triggering DFS. (80>40>20)

1832 in particular has a chipset which is particularly prone to false radar detection.

A number of fixes went in to reduce those false detections but you'll need the latest 8.5 code to pick up those fixes.

If you're staying on that old code then stick to 20MHz channel width.

[Scott Fella]

Typically you should not see any issues when you move from 20 to 40.  I have seen issues in the past with 40mhz when the client wireless nic is running an old firmware.  If you have every single device, even newer mobile phones that drop, then I would agree with others and its the code.  So check both and maybe you will have to upgrade the 5508 and also upgrade nic firmware.