A method for monitoring an optical fiber link comprises generating a monitoring signal used for monitoring the optical fiber link, combining the generated monitoring signal with a data signal to be transmitted over the optical fiber link, detecting backscattering of the monitoring signal from the optical fiber link, detecting a change in characteristic of the detected backscattered monitoring signal, and determining, from the detected change in characteristic, at least one location along the optical fiber link where the monitoring signal is modified, and signal loss at this location.