This counter records the number of bits transmitted out of this Ethernet port during the final one-second sample before this archived history bin was closed. It lets the admin confirm whether outbound traffic was still active at the exact moment the historical interval ended, useful when investigating a port failure that occurred right at an interval boundary. For example, if a port failure was logged right at midnight, the admin would check cmEthernetTrafficPortHistoryIBRTx from that day's closing bin to see if transmission had already stopped before the failure was recorded.