Spectrum Defragmentation with Improved Lightpath Migration Scheme in Flex-grid Networks

The currently deployed fixed-grid Wavelength Division Multiplexing (WDM) technology is expected to be replaced by the more dynamic flex-grid WDM, which requires advanced methods for connection management and control (e.g., lightpath set-up and (re)configuration). The dynamic arrivals and departures of lightpaths often leave behind spectrum holes, causing fragmentation. In addition, reconfiguration of lightpaths often entails lightpath migrations that might cause disruptions of existing connections. Lightpath disruptions are expensive, as penalties will result as compensation for the violation of the service level agreements. In this paper, we analyze and identify the deficiencies of some existing work that tackles this problem. In particular, we show that the minimization of High-slot Marks might still lead to some fragmentation. Besides, these approaches neglect the lightpath configuration delays in the migration process. We develop optimization models that evidently better cope with these deficiencies. The performance improvements of the models are validated in a selected network scenario. The results also open up further research possibilities to better understand and model the trade-off between defragmentation gain and the degree of lightpath disruptions.