This is the cumulative frames received counter: the running total of FC frames this port has received since its counters were last reset (e.g. at a port or fabric interconnect reboot). On one specific historical error-statistics snapshot for an FC port, this is the lifetime tally, so on its own it is just a traffic volume gauge, but a flat value on a port that should be carrying storage I/O is a fast way to spot a link that is up but silently passing no traffic. For example, a 32Gbps port serving an active datastore accumulates roughly 200 million frames a day; a sudden flatline while operState still shows up flags a stuck path rather than a link-down event.