The Cisco ONS 15540 ESPx is an optical transport platform that employs DWDM (dense wavelength division multiplexing) technology. With the Cisco ONS 15540 ESPx, users can take advantage of the availability of dark fiber to build a common infrastructure that supports data, SANs (storage area networks), and TDM (time-division multiplexing) traffic. The system uses an enhanced chassis with front fiber-optic cable access for optical interconnections between transponders and optical mux/demux modules.The Cisco ONS 15540 ESPx is a 12-slot modular vertical chassis. The system uses redundant 48 VDC inputs. A redundant external AC-input power supply is available or DC-input power can be provided directly. Slots 0 and 1 hold the optical mux/demux motherboards, which are populated with optical mux/demux modules. Slots 2 to 5 and 8 to 11 hold the line card motherboards, which are populated with transponder modules. Slots 6 to 7 hold the processor cards. The air intake, fan assembly, cable management tray, cross connect drawers, and cable storage drawers are located beneath the modular slots. The system has an electrical backplane for system control. The Cisco ONS 15540 ESPx chassis features external cross connect capability.