Chromatic dispersion is determined based on the arrival times of different frames of data in a wavelength division multiplexed (WDM) system having an optical communication link. Namely, a first frame is transmitted on a first optical channel, which is supplied to the optical communication link. A second frame is then transmitted on a second optical channel and the transmission time difference between the two frames is obtained. At a receive end, the difference in arrival times of the two frames is measured to obtain a relative time delay between the first and second frames and used to determine a chromatic dispersion.