This field reports the total number of octets transmitted on this PM instance, exposed here as cienaCesPmExtendedTxRxStatsBinTxTBytes. On this Ciena CES port's PM data, the description for this field is essentially identical to the sibling TxBytes counter ('total number of octets transmitted' vs 'number of octets transmitted'), so in practice it's Ciena's secondary cumulative-labeled egress byte counter for the same PM instance — the two should track each other closely, and any persistent, growing gap between them on this port is itself worth flagging rather than assuming they're simply redundant; and this sits in the currently active extended Tx/Rx interval bin — its sibling StartTime/ClearTime fields mark exactly which window is being counted, so a change here reflects activity happening in the live collection interval, not something already filed away in history. For example, a moderately busy port showing 78,000 total bytes transmitted for this bin would be a plausible, unremarkable reading.