  We report a cascaded optical link of 1100 km for ultra-stable frequency
distribution over an Internet fiber network. The link is composed of four spans
for which the propagation noise is actively compensated. The robustness and the
performance of the link are ensured by five fully automated optoelectronic
stations, two of them at the link ends, and three deployed on the field and
connecting the spans. This device coherently regenerates the optical signal
with the heterodyne optical phase locking of a low-noise laser diode. Optical
detection of the beat-note signals for the laser lock and the link noise
compensation are obtained with stable and low-noise fibered optical
interferometer. We show 3.5 days of continuous operation of the
noise-compensated 4-span cascaded link leading to fractional frequency
instability of 4x10-16 at 1-s measurement time and 1x10-19 at 2000 s. This
cascaded link was extended to 1480-km with the same performance. This work is a
significant step towards a sustainable wide area ultra-stable optical frequency
distribution and comparison network at a very high level of performance.
