Optimizing Spectrum Allocation in Flex-grid Optical Networks

In this paper we propose a spectrum defragmentation algorithm applicable to fixed-grid and flex-grid wavelength division multiplexing (WDM) optical networks. The algorithm is formulated as an Integer Linear Program (ILP) which aims at recalculating the spectrum allocated to existing lightpaths in the network, thereby increasing the amount of spectrum made available for future connections. This is achieved by minimizing the spectrum fragmentation on the network links. The approach provides a strategy to migrate lightpaths from their existing configuration to the new optimized one while minimizing (at its best) the number of lightpath disruptions. The results show that spectrum defragmentation on individual links is attained at the expense of a higher complexity in the migration process. The algorithm is compared with an existing ILP approach by using different testing scenarios. A mathematical complexity analysis is performed to study the impact of different model parameters on the computational complexity of the method.