The IEEE 802.1ab frame delay measurement (ETH-DM) function is used for on-demand operation administration and maintenance (OAM). ETH-DM is employed when measuring the frame delay (FD) and frame delay variation (FDV), where the FD refers to the interval between the time when the first bit of a frame is transmitted by a source node and the time when the last bit of the frame is received by the same source node after the frame is looped back. Frame loopback is performed by the destination node of the test. ETH-DM allows the FD and FDV measurements to be performed on each endpoint in two distinct modes: one way, or unidirectional, where the endpoint clocks are not synchronized and two-way, or bidirectional, where they are.