This article applies to all the controllers running AOS version 220.127.116.11 and higher.
In order to collect information about its RF neighborhood, APs scan every scan interval for a predetermined amount of time.
AP radios may defer these periodic scans if there is any station in Power-Save (PS) mode associated to them. In most deployments (especially with mobile devices), the likelihood of having a client in PS mode is quite high. This results in long periods of time where radios do not scan which may lead to age out and neighbor rediscovery. In 6.1, power-save-aware scanning has been set to disabled by default. This has improved the scanning efficiency substantially.
Even then, there are other reasons where the AP may defer its scans due to consistent traffic load or the presence of voice or video sessions, which may result in loss of information. Below enhancements are made in AOS version 18.104.22.168 to address these issues:
- Dynamic scanning
Default scanning interval is controlled by the scan-interval knob in the ARM profile. This is set to 10 seconds, which means that every 10 sec + jitter, the AP scans a new non-home channel. In the absence of clients (or with inactive clients), dynamically readjusting scan interval can give the AP more opportunities to scan and maintain up-to-date information about the RF neighborhood across the spectrum. Here is the new scanning behavior -
- Scan every second if no clients are associated
- Scan every 5 seconds if more than 80% clients are idle
- Else scan every 10 seconds
- Feedback from driver about scan result
In the current model, the Air Monitor (AM) does not have knowledge of whether the scan was successful or not and attempts to scan the next channel. In 5GHz band, there can be up to 24 channels to scan and it may take a while before the same channel is scanned again.
By adding feedback about the scan status, AM attempts to rescan the skipped channel once. Additionally, AM can maintain stats about unsuccessful scans and if they exceed a threshold, a trap can be generated for Airwave reporting.