Seamless Upgrade from C+L to C+L+S Bands in Optical Networks with Interim Lightpath Re-Allocation

Network operators tend to migrate multiband optical networks to wider bands by batch upgrade (i.e., with a pay-as-you-grow strategy affecting only a subset of links at a time). However, temporary interruptions of services routed along the fibers that require equipment upgrades can create significant service blocking, which can only be avoided with interim lightpath re-allocation during the upgrade period. To seamlessly upgrade the network from C+L to C+L+S bands, we propose a batch upgrade strategy to reduce the upgrade cost, and a band-selective re-allocation method during the upgrade period to minimize blocking probability (BP). Simulations on the US-24 topology demonstrate up to nearly 50% cost reduction and BP as low as 0.3%.