This field records how much the counter for FCoE payload bytes transmitted out this same converged Ethernet uplink toward the fabric changed during the specific collection interval this historical record captured — a frozen snapshot of that one interval's increase, not a live running total. For a network admin, comparing this against bytesRx on the same interface shows whether the FCoE conversation is asymmetric, e.g. a host mostly reading from a SAN-attached LUN. For example, a value of 784,814 bytes would mean that much FCoE data crossed this uplink in just the last collection interval.