Channel utilization is one metric we use to gauge Wi-Fi performance. Understanding congestion at the access point (AP) level can mean a few different things.
A more standards-based term for this is Basic Service Set (BSS) Load. It is defined in the 802.11 standard and part of 802.11e. It was formally called QBSS Load.
BSS Load is a method for an AP to communicate channel usage. And in a perfect world, devices can use this information to select better AP candidates for roaming.
Besides channel usage, or utilization, BSS Load can advertise how many devices are associated to an AP. But the number of associated devices does not necessarily correlate with a specific amount of channel utilization.
You can find the BSS Load details inside a beacon frame. Within the BSS Load element there is a Channel Utilization and Station Count field.
The way Channel Utilization field is defined by a percentage of time with 255 representing 100% of that AP sensed the medium was busy. This is done by physical or virtual carrier sense. What this means it is possible to have one or more associated devices (also called a station) occupying most of the medium.
It’s important to note that the Channel Utilization is only calculated for the primary channel (as the standard says.)
The Station Count field tells you how many devices are associated to that BSS or AP.
If multiple APs were operating on the same channel in the same area, you would see similar Channel Utilization on both BSS’. Since the APs would be sensing the medium for that same channel.
Other ways you could find BSS Load is using a spectrum analyzer such as the Ekahau Sidekick. In my examples, I have used WiFi Explorer Pro – which obtains channel utilization from the BSS Load element. It is gathered the same way when looking at it from a frame capture.