This read-only integer reports the cumulative time, in seconds, this port spent handling fax calls specifically. It matters to an admin distinguishing traffic types on a mixed-use channel, particularly since fax over VoIP can behave differently, and fail differently, than voice. For example, an unexpectedly high totalFaxUsage on a port meant primarily for voice traffic might indicate machines auto-dialing fax retries that are consuming capacity intended for voice calls.