Understanding Channel Trashing and What to do About it
- Radio Resource Management (RRM) is a technology used by most access point vendors that simplifies Wi-Fi network management by removing the need to manually assign radio channels or adjust the power levels for each access point. With RRM enabled access point controllers can automatically adjust radio channel assignments and power levels to help:
- Reduce interference between your access points or interference with neighboring access points in the area, thus maximizing Wi-Fi bandwidth to help maintain the efficiency of communication over the wireless network. At a specified interval, the access point controllers map APs to channel use and measure interference levels in the networks. If significant channel interference is detected, the access point controller automatically re-assigns some or all of the APs to new channels per an efficiency algorithm (or automated channel plan).
- Improve wireless network coverage by automatically increasing or decreasing access point transmission power levels.
RRM can really simplify daily Wi-Fi network maintenance if used correctly, but it could also cause major network connectivity issues when not properly configured.
One of the most common problems caused by a misconfigured RRM is Channel Trashing. Channel Trashing happens when RRM tries to compensate for high levels of RF interference by constantly changing access point radio channels, which in turn causes all client devices connected to the access points to disconnect from the network every time channel assignments change. In the best of cases, Channel Trashing will cause random disconnects throughout the day, but in the worst-case scenario it could make the wireless network unusable.
So, how can you determine that those random disconnects your seeing throughout the day are caused by channel trashing? The best way to identify Channel Trashing is by monitoring the Wi-Fi network throughout the day and count how many times the channels being used by your access points change. If you see that RRM is changing channels more than once a day that means you have two problems:
- There is a high level of interference on the area where the access points that keep changing channels are located.
- RRM has been configured to be too aggressive, thus causing it to change access point radio channels too often.
How do you fix the problem? A few things can be done to help resolve problems with Channel Trashing:
- Configure RRM to only change channels once a day, and during a time of the day with low network traffic (not a lot of people connected to the network).
- Identify sources of RF interference in the area and remove them. If it is not possible to remove the source of the RF interference, reconfigure RRM so it won’t try to use the affected channels.
Identify channels not impacted by the interference, disable RRM, and manually assign channels to each access point. This solution is a lot more work since you will have to manually create a channel plan, but it has been known to greatly help on areas with high interference.