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We report an optical link of 540 km for ultrastable frequency distributionover the Internet fiber network. The stable frequency optical signal isprocessed enabling uninterrupted propagation on both directions. The robustnessand the performance of the link are enhanced by a cost effective fullyautomated optoelectronic station. This device is able to coherently regeneratethe return optical signal with a heterodyne optical phase locking of a lownoise laser diode. Moreover the incoming signal polarization variation aretracked and processed in order to maintain beat note amplitudes within theoperation range. Stable fibered optical interferometer enables opticaldetection of the link round trip phase signal. The phase-noise compensated linkshows a fractional frequency instability in 10 Hz bandwidth of 5x10-15 at onesecond measurement time and 2x10-19 at 30 000 s. This work is a significantstep towards a sustainable wide area ultrastable optical frequency distributionand comparison network.

Ultra-stable long distance optical frequency distribution using the Internet fiber network