This read-only integer reports the cumulative time, in seconds, this port has spent on data-transfer or modem calls, the third traffic-type bucket alongside voice and fax usage. Admins use it to see whether a port is carrying legacy modem/data traffic in addition to voice, which can affect capacity planning differently than pure voice trunking. For example, a port on an otherwise voice-focused trunk group showing significant totalDataUsage would flag unexpected modem traffic worth investigating.