  We report an optical link of 540 km for ultrastable frequency distribution
over the Internet fiber network. The stable frequency optical signal is
processed enabling uninterrupted propagation on both directions. The robustness
and the performance of the link are enhanced by a cost effective fully
automated optoelectronic station. This device is able to coherently regenerate
the return optical signal with a heterodyne optical phase locking of a low
noise laser diode. Moreover the incoming signal polarization variation are
tracked and processed in order to maintain beat note amplitudes within the
operation range. Stable fibered optical interferometer enables optical
detection of the link round trip phase signal. The phase-noise compensated link
shows a fractional frequency instability in 10 Hz bandwidth of 5x10-15 at one
second measurement time and 2x10-19 at 30 000 s. This work is a significant
step towards a sustainable wide area ultrastable optical frequency distribution
and comparison network.
