  We describe the use of fiber Brillouin amplification (FBA) for the coherent
transmission of optical frequencies over a 480 km long optical fiber link. FBA
uses the transmission fiber itself for efficient, bi-directional coherent
amplification of weak signals with pump powers around 30 mW. In a test setup we
measured the gain and the achievable signal-to-noise ratio (SNR) of FBA and
compared it to that of the widely used uni-directional Erbium doped fiber
amplifiers (EDFA) and to our recently built bi-directional EDFA. We measured
also the phase noise introduced by the FBA and used a new and simple technique
to stabilize the frequency of the FBA pump laser. We then transferred a
stabilized laser frequency over a wide area network with a total fiber length
of 480 km using only one intermediate FBA station. After compensating the noise
induced by the fiber, the frequency is delivered to the user end with an
uncertainty below 2x10-18 and an instability sigma(tau) = 2x10-14/(tau/second).
