A migration from fixed-grid WDM networks to flexible-grid networks is foreseen as a solution able to cope with the constant traffic increase in backbone networks. The migration will involve significant changes in the network infrastructure and in the architecture of optical switching nodes. Indeed, several studies propose new architectures that can effectively exploit the characteristics of flexible-grid networks. On the one hand, traditional ROADM nodes enhanced with new colorless, directionless and contentionless capabilities are studied. On the other hand, nodes designed according to the Architecture on Demand concept were proposed as a solution able to dynamically adapt to the elastic switching and processing requirements of flexible-grid networks. We evaluate the two node architectures considering their use in flexible-grid networks and we compare their spectral efficiency and energy consumption
