Dense Wavelength Division Multiplexing (DWDM) is a revolutionary technology, with point-to-point DWDM system representing the first phase in the evolution of Optical Transport Networking. DWDM is the most cost-effective way to expand capacity than some other alternatives such as adding fibre or replacing current capacity (say 2.5 Gbps) Time Division Multiplexing (TDM) systems with new higher bit-rate (say 10 Gbps) TDM systems. Laying new fibre is expensive, particularly for long routes, and its installation can take too long to satisfy customers. TDM technology is no longer able to keep pace with the emerging ultra-broadband data backbone demands.