Provisioning, Recovery, and In-Operation Planning in Elastic Optical Networks

3 The Routing and Spectrum Allocation Problem

Luis Velasco¹, Marc Ruiz¹ and Mirosław Klinkowski²

¹ Universitat Politècnica de Catalunya, Barcelona, Spain

² National Institute of Telecommunications, Warsaw, Poland

To properly design, operate, and reconfigure Elastic Optical Networks (EONs), the routing and spectrum allocation (RSA) problem must be solved. Regardless of additional constraints, the RSA problem involves two main constraints for spectrum allocation: 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. These two constraints highly increase the complexity of the optimization, so it is crucial that efficient methods are available to allow solving realistic problem instances in practical times. In this chapter, we review several Integer Linear Programming (ILP) formulations of the RSA problem and evaluate their performance regarding the computational time to solve a basic offline problem.

From the basic RSA problem, additional variables and constraints can be added to consider various EON key features. Among them, the capability of selecting the required modulation format among the available ones becomes essential for a vast set of EON optimization problems. Therefore, the routing, modulation, and spectrum allocation (RMSA) problem is eventually presented as the most relevant basic optimization problem, and, ...