The 15454-GBIC-ZX operates on SMF optic link spans of up to 80 km in length. Link spans of up to 100 km are possible using premium SMF or dispersion shifted SMF. When shorter distances of SMF are used, it may be necessary to insert an in-line optical attenuator in the link, to avoid overloading the receiver. For fiber-optic cable spans less than 25 km, insert a 10 dB in-line optical attenuator between the fiber-optic cable plant and the receiving port on the 15454-GBIC-ZX at each end of the link. For fiber-optic cable spans equal to or greater than 25 km and less than 50 km, insert a 5 dB in-line optical attenuator between the fiber-optic cable plant and the receiving port on the 15454-GBIC-ZX at the end of the link.