Patent ID: 8873947

Claim:
A method of deriving a characteristic of a span of optical fiber between a first node and a second node in a wavelength division multiplexing (WDM) optical communication system, comprising: at the first node, transmitting at least one loopback instruction toward the second node via an optical supervisory channel (OSC) over the optical fiber, the loopback instruction adapted to cause the second node to enter a loopback mode of operation, the loopback instruction comprising a packet having a first predetermined bit pattern; at the first node, transmitting according to a first clock, at least one first measurement signal toward the second node via the optical supervisory channel, the measurement signal comprising a packet having a second predetermined bit pattern; at the first node, recovering according to a second clock, via the optical supervisory channel at least one second measurement signal, each second measurement signal comprising a loopback signal associated with a corresponding one of the at least one first measurement signal; determining a roundtrip time associated with the transmitting of the at least one first measurement signal and the recovering of the at least one corresponding second measurement signal; and calculating at least one fiber characteristic based on the roundtrip time.