Higher-order modulation formats and spectral super-channels are key to maximizing spectral efficiency (SE) in next-generation optical transport networks, thereby postponing/minimizing expensive additional fiber rollouts and reconfigurable optical add/drop multiplexer node upgrades. A flexible dense wavelength division multiplexed (DWDM) grid is key to efficiently accommodating media channels requiring more (or less) than 50 GHz of contiguous spectrum. In particular, routing media channels consisting of multiple adjacent carriers enables packing them closer together and sharing a single pair of guard bands of adaptive width to cope with optical filtering. This effect is maximized by giving preference to deploying media channels with more carriers. However, designing the DWDM network in such a way can translate into resource overprovisioning whenever the traffic requirements between two nodes are below the (large) capacity of the most spectrally efficient media channel format that can be deployed between those nodes. This paper provides insight on how the set of media channels and the network design framework used impact the trade-off between maximizing SE and minimizing resource overprovisioning in transparent flexible-grid optical networks. Furthermore, it discusses enabling strategies to mitigate the risk of resource overprovisioning when maximizing network SE is the key design objective.
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