WIFI connection issues - Reported: I have a single classroom that shares an AP650 from another room (connected classroom) that uses Chromebooks for Math assignments. Students report devices drop connection or won't connect.

[rkowals]

The room shares an AP650 next door, students report slow connections or dropped connection on their chromebooks. I have yet had any other issues with other classrooms setup the same way. II bumped the Transmission for both radios from Auto to manual and adjusted the power to 20dBm for both, both wirelesss interfaces are set for 5ghz, no SDR. I've attached the commands I normally would run to see of any transmission issues. I have 4 other classrooms setup the same way, no issues or complaints, in the same area.

[samantha_lynn]

Those recommended settings will help clean up the air space you're using, which will reduce packet damage so that all looks correct to me.

In a lab environment the AP650 can hold up to 255 clients per radio, however we typically won't see that kind of client load in a non-lab environment. It will depend on what the clients are trying to do (email vs streaming for example) and what the environment is like.

Having one, more powerful, AP cover several class rooms will work to a point, but the more obstacles between the AP and the client devices (for example walls, desks, other people, reflective surfaces, water, smart boards, other wireless signals from a printer or other similar IoT device, etc), the more damage the signal will take.

[rkowals]

Sam,

I made some changes to the radio profiles from surrounding AP’s. We will see how well they do when students come back next week. Can you tell me what’s the maximum amount of connections we should have for an AP650. When discussing upgrading to the newer models, we were told they would handle twice as many devices than the older 230/250 units we have. With that in mind, we replaced many of the older units in the classrooms and alternated new AP’s between classrooms so that a single AP would cover more than one classroom. I went ahead an opened a ticket with Tech Data I pulled from the AP and among changing manual power settings , this is what was sent to me. See if you might agree with it,

Enable DFS channels (no sub options) 

-Disable MU-MIMO 

-Disable transmit beamforming

thanks again

[samantha_lynn]

Thank you for that output. The first output for "show acsp neighbor" is showing some loud neighboring signals, that will be causing signal overlap, which causes signal damage, which causes retries, which shows up as slow wireless speeds or frequent disconnections. The neighbors that have an RSSI value in the -50's are too loud, and need their power adjusted lower so we aren't overlapping the signals between the two APs so much. The devices that you'll want to lower the power on have MAC addresses starting with: 3485:843c:e2 and 3485:843c:d4. Those MAC addresses are missing the last two characters (because the output we're looking at changes those last two characters to indicate different interfaces from the same AP), but you should be able to find those devices with the partial MAC address in your device inventory. I'd recommend lowering the power on these APs by 2dBm per test, to avoid causing any sudden dead zones.

The next output regarding the wifi0 interface shows high collision (again indicating packet damage), and a CRC failure rate of 34%. That means that 34% of the traffic received by this AP is too damaged to read the first time, and had to be resent at least once (likely more than once) before it was readable and the AP could move on to the next packets.

The output regarding the wifi1 radio shows high collision as well, with a CRC failure rate of 51%. Again that means that 51% of the traffic received by the wifi1 radio is too damaged to read and had to be resent at least once.

CRC failures are typically caused by environmental issues. You'll want to make sure the front of the AP is facing the area where the client devices are going to be, and that the AP is as far away as possible from any metal, glass, or water. Any reflective surfaces like these will fragment your signal and cause those CRC failures and retries.

Overall there is significant interference on this AP, that could explain the symptoms you're experiencing. This guide reviews in more detail how to identify interference and how to troubleshoot it on your network: https://thehivecommunity.aerohive.com/s/article/Radio-Frequency-Interference-NG