US Patent 9432144 Precision time transfer systems and methods in optical networks

A precision time transfer method, in a first node that communicates with a second node, to determine a difference in time between the first node and the second node, the precision time transfer method includes receiving a departure time, TD-A, from the second node, wherein the departure time is determined by the second node based on detecting a timing marker in a Forward Error Correction (FEC) frame or logical layer; determining an arrival time, TA-B, based on detecting the timing marker in the FEC frame; and determining a time difference based on the departure time and the arrival time wherein the timing marker is detected at a last point in a transmitter of the second node and at a first point in a receiver of the first node, during FEC processing.