On the value proposition of the contentionless add/drop ROADM property in DWDM transport networks

New ROADM nodes being deployed in DWDM transport networks can already benefit from add/drop structures that support both colourless and directionless properties, thereby enabling to transmit/receive signals to/from any wavelength and direction. Depending on the ROADM architecture, these two properties can be further enhanced by the contentionless one, which guarantees that any free add/drop port can be used for a given wavelength and direction regardless of whether the same wavelength is already in use via other add/drop ports. The relevance of the later property has been the subject of debate in the literature and industry. This paper overviews the value proposition of contentionless over a multi-period planning scenario, aiming to highlight to which extent avoiding contention at the add/drop side is expected to provide savings in operational expenditures.