WDM fiber links carry a number of wavelengths, with each wavelength typically having a capacity of 10 Gbps or 40 Gbps. 40 to 80 wavelengths per fiber are common. Optical amplifiers are necessary at intervals of about 80 km to make up for signal attenuation. With the finite range of light paths (depending on the line rate and technology employed, this is in the order of 1000 to 4000 km), long links require regeneration of the optical signal.