Terminal always loss WiFi connection and connect again by ACU2 with V200R006C10SPC200 version

Publication Date:  2016-12-27 Views:  343 Downloads:  0
Issue Description

There are two ACU2 with V200R006C10SPC200 version worked as hot-standby to provide WiFi for office users. But users have complaint that terminal always loss WiFi signal and connect WiFi again without moving. All AP5010 with V200R006C10SPC900 version online during this times.

Handling Process

1: Monitor the terminal, make ping test from ACU2 to terminal. At 10:48, pig test time out:

2: Make rf-ping test at that moment, it still loss pakcets.

Rf-ping means establish the physical link with the terminal. At this time, the terminal does not respond the ACK.
3: Make AP packet statistics at same time
Check the AP packet statistics, the packet send of the AP is normal. Totally ping 19 packets, all of them are no ACK

4: At 10:51 AM, Station Roaming, business recovery.

5: Check the AP status, find the AP calibrate at that moment:

View the channel switch record shows that the AP has a calibration. Indicating that there is indeed interference at this time.
At the same time, we can see, there are several times of DFS switch records, it means of radar detection, there may be channel switching risk.
6: Analysis the AP status where has a lot of complaints from users.
This AP switch the channel number reached 36 times in the past two days, 19 times for radar, and 17 times for calibration.

7: Analysis why there are so many calibration caused by the DFS.
Radar channel detection is a basic function of WLAN products. Based on the provisions of the protocol, when the AP detected the radar signal, it is required to change channel to avoid. At the same time, because the European country code, from 52-140 channels are radar channels, switch to this radar channel, this time need to silence for a few seconds, weather channels such as 120,124,128 channels need to silence 10min. At this time may cause customer service interruption.
The current network customers use the 80M bandwidth for 5G, a bandwidth occupied by four channels. If one of the four channels found radar signal, need to avoid, and will also join the current 80M bandwidth channel in the blacklist 30min.
8: Change the bandwidth for 5G to 20MHz in order to decrease the radar detection possibility and increase the available channel.
9: Monitor the AP status, it will not always change channels. And all the terminal work well without losing WiFi service.

Root Cause
The current network customers use the 80M bandwidth for 5G, a bandwidth occupied by four channels. If one of the four channels found radar signal, AP will was forced to change the channels. So it will increase the calibration possibility. One time of calibration means terminal need to reconnect the WiFi one time.
Because this interference was caused by the radar. So AP must change the channel even when AP didn’t active the auto-calibration feature.
So just can reduce the possibility of changing channel by decrease the bandwidth of 5G.
1: If there are a lot of interference from radar or weather channel. We’d better to configure a narrow bandwidth instead of 80MHz in order to make sure the user experience.
2: For the AP6510DN/AP6610DN/AP8030DN with version V2R6C10SPC300 or previous version. When AP always calibrate caused by the DFS, the 5G channel will be blocked and never available again. This is a bug for production, just need to upgrade AP to V200R006C10SPC500 or later version, it will be solved.