The dashboard displays RSSI metrics in two different areas:
- the RSSI chart on the Wi-Fi status page and sensor states page
- the RSSI value for an SSID in the Wi-Fi Environment panel on the sensor status page
These values are calculated in very different ways and as a result there may be discrepancies between values reported for the same BSS.
RSSI on the Wi-Fi Environment panel
This RSSI value is retrieved from AP management frames. In particular, beacon frames and probe responses. We do an AP scan across channels periodically and the RSSI values shown here are the values observed from the aforementioned management frames during the most recent scan.
This is a common method of gathering RSSI data for a number of SSIDs and should be familiar to users and comparable to the output of a Linux command like iw scan.
RSSI on charts
RSSI charts appear on the sensor status page and the Wi-Fi status page. These charts use RSSI measured in a very different way to the RSSI displayed on the Wi-Fi environment panel and shouldn't be compared to those values.
The methodology for calculating this RSSI value is as follows:
- The sensor inspects every frame transmitted by the BSS it is connected to that is destined for the sensor
- It excludes any WLAN frame that is not a data frame (for example, management frames are not included in the calculation)
- It excludes any WLAN frame destined for other clients
- RSSI values are gathered and the average (mean) is taken per minute
Why this methodology?
This methodology of calculating RSSI from data frames destined for the sensor only gives us a more nuanced, reliable measurement of the RSSI that affects application performance. Disregarding transmissions for other clients excludes any potentially inaccurate readings that could result from technologies such as beam-forming. Disregarding broadcast / management frames similarly means that we're aggregating RSSI only from frames that affect application performance and thus user experience.
We maintain the RSSI values in the Wi-Fi environment tab for context of how the RSSIs of your APs and BSSes compare.