The Cisco ONS 15540 ESP (Extended Services Platform) is an optical transport platform that employs DWDM (dense wavelength division multiplexing) technology. With the Cisco ONS 15540, 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 Cisco ONS 15540 is a 12-slot modular vertical chassis. The system is powered by 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.