Routing and Spectrum Allocation

To properly analyze, design, plan, and operate flex-grid networks, the routing and spectrum allocation (RSA) problem must be considered. The RSA problem involves two basic constraints: the continuity constraint to ensure that the allocated spectral resources are the same along the links in the route, and the contiguity constraint to guarantee that those resources are contiguous in the spectrum. Moreover, since advanced tunable transponders are envisioned for flex-grid networks, their configuration along with physical layer considerations need to be included in the optimization process. As a consequence of the RSA complexity, it is crucial that efficient methods are available for solving realistic problem instances in reasonable time. In this chapter, we review different variants of the RSA optimization problem; different methods to solve those variants are reviewed along with different requirements related to where those variants are applicable. Starting from a general RSA formulation, we analyze the network life-cycle and discuss different solving methods for the problems that arise at each particular network cycle: from offline to in-operation network planning. We tackle three representative use cases: (1) a use case for offline planning where a demand matrix need to be served taking into account physical layer impairments; (2) a use case for offline planning where a flex-grid network is designed and periodically upgraded; and (3) elastic bandwidth provisioning once the network is being operated.