Switch port availability calculation

TLDR: how is the network interface port usage value calculated?

I hadn’t noticed the Other > Switch port statistics view until today. Clicking into a given host, I can see the Network Interfaces: Network Interface: Port Usage value in the invinterface_of_host view, but it’s not clear to me how the Port Usage status is being calculated. Can anyone enlighten me?

Port availability would be useful for us, but without knowing how the value is calculated, we’re not sure whether to trust it or not.

A port is flagged “free” after being 30 days in operational state down.

The timespan can be configured with the ruleset “Parameters for switch port inventory”.