The operation to be taken by the node that receives the echo reply in response to its echo request depends on its current mode of operation such as ping or trace.
In ping mode, the node may choose to ignore the target FEC 128 in the echo reply and report only the return code to the operator.
However, in trace mode, the node builds and sends the subsequent VCCV echo request with a incrementing TTL and the information (such as the downstream FEC 128) it received in the echo request to the next downstream pseudowire segment.