Wavelength Defragmentation for Seamless Migration

Dynamic traffic in optical networks leads to spectrum fragmentation, which significantly reduces network performance, i.e., increases blocking rate and reduces spectrum usage. Telecom operators face the operational challenge of operating non-disruptive defragmentation, i.e., within the make-before-break (MBB) paradigm when dealing with lightpath rerouting in wavelength division multiplexed fixed-grid optical networks. In this paper, we propose an MBB routing and wavelength assignment defragmentation process, which provides the best possible lightpath network provisioning, i.e., with minimum bandwidth requirement. We tested extensively the models and algorithms we propose on four network topologies with different grade of service defragmentation triggering events. We observe that, for a given throughput, the spectrum usage of the best MBB lightpath rerouting is always less than 2.5% away from that of an optimal lightpath provisioning.