WiFi Disconnect and High Latency

[fdharmawan]

Hi Guys,

Some clients on my deployment started to experience random disconnection (1-2 reports per week) and high latency issue. I was thinking it was related to the AP uptime that was close to a year. So I restarted all the APs but the issue still persists.  I checked on the PI report, it only shows the disconnection time of the client, I could not get any further information.

May I know when to start the investigation? Because the issue happens on random laptops, while the other laptops with the same model was fine. And the issue did not repeat on that client, that's why I am not sure the issue was client related.

My deployment is WLC 5520 with 3802 access points. 

Thank you.

[Leo Laohoo]

1. What are the models of the APs?
2. What firmware are the controllers on? 
3. What sort of wireless clients, laptops, smartphones, tablets, etc?

[fdharmawan]

Hi Leo,

The APs are Cisco 3802, while the WLC is 5520. The firmware is 8.10.162.0. The clients are laptops, Lenovo Thinkpad T series with dot1x authentication.

[Leo Laohoo]

There are many bugs affecting 2800/3800/4800/1562 and AireOS.  The issue revolves around the MARVAL radio chipset the APs have on them.  When the bug hits, the chipsets either "delays" the traffic or, in a lot of cases, blackholes them. 

Please refer to:  https://community.cisco.com/t5/wireless/can-the-wlc-capture-be-trusted/m-p/4789600

Just as a test, disable WMM on the SSID and see if it improve things. 

[fdharmawan]

Hi Leo,

May I know what are the consequences that I am looking if I disable WMM? I read Rasika's post about WMM (https://mrncciew.com/2013/07/30/wmm-qos-profile/) but I still do not get the whole picture of the pros or cons in disabling WMM. What I understand is that WMM needs to be allowed in order to get a better rate for voice in WLAN deployment.

[Leo Laohoo]

---

@fdharmawan wrote:
May I know what are the consequences that I am looking if I disable WMM? 

---

Turning off WMM is neither a workaround nor a solution. 

This is an exploratory move to determine if, disabling the WMM, would improve the situation or make it worse.  

If it improves, turn WMM back on but this confirms that the bugs I've mentioned is indeed present.

[marce1000]

 - Make sure wifi driver(s) are up to date on all the laptops , also consider : https://www.cisco.com/c/en/us/support/docs/wireless/wireless-lan-controller-software/200046-tac-recommended-aireos.html

 M.

[JPavonM]

I would suggest you to make further analysis of the issues:
- Does it happen at a specific time of the day? If so, investigating what's going on in the network could be fine.
- How many devices can you see there are connected to the same radio and channel when the users start complainng?
- How is it the channel utilization or TX/RX utilization when this happen? If there is high utilization, can you track down this to specific device/s with high load? (file transfer, remote load, high BW streaming, ...)
- How does it like the signal strength and SNR for the clients that complaint?

Also remember that latency and traffic issues could be due to the LAN and WAN, or the remote service been accessed.

Hope this help.

[Gaurav Kansal]

Dear Fdharmawan,

Please go through this link : https://www.cisco.com/c/en/us/td/docs/wireless/controller/release/notes/crn810mr6.html#open-caveats

Maybe your access points are hitting bug. Please read open caveats related to 3800 series access points.

GoodLuck..