Wavelength Assignment for Concatenated ROADM Ring Networks and Switch Scale Reduction in a Concatenating Node

We propose a wavelength assignment algorithm that offers full-mesh node connectivity of two concatenated, bidirectional ring networks. This algorithm is proved to minimize the necessary number of wavelengths. We also describe three schemes that can reduce the switch scale at the ring-concatenating nodes: separation of intra-ring and inter-ring operation, hierarchical optical path switching, and introduction of efficient protection switching. We clarify that the proposed node architectures applying the described schemes reduce the switch size by 50% to 75% compared with the conventional arrangement.