Cisco GLC-ZX-SM SFP Module is 1000BASE-ZX SFP. This is a Duplex SFP transceiver for optical communications, rated for distances up to 70 km and a maximum bandwidth of 1Gbps. The GLC-ZX-SM transceiver operates at 1550nm wavelength. The 1000BASE-ZX SFP operates on standard single-mode fiber-optic link spans of up to approximately 70 km in length. The SFP provides an optical link budget of 23 dB, but the precise link span length depends on multiple factors such as fiber quality, number of splices, and connectors.