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1. GSNR-aware resource re-provisioning for C to C+L-bands upgrade in optical backbone networks

   https://doi.org/10.1007/s11107-024-01023-6  

   Kalkunte, Ramanuja; Jana, Rana_Kumar; Ferdousi, Sifat; Srivastava, Anand; Mitra, Abhijit; Tornatore, Massimo; Lord, Andrew; Mukherjee, Biswanath (July 2024, Photonic Network Communications)

   Abstract Efficient network management in optical backbone networks is essential to manage continuous traffic growth. To accommodate this growth, network operators need to upgrade their infrastructure at appropriate times. Given the cost constraint of upgrading the entire network at once, upgrading the network periodically in multiple batches is a more pragmatic approach to meet the growing demands. While multi-period, batch-upgrade strategies to increase network capacity from the conventional C band to C+L bands have been proposed, they did not consider so far the possibility to re-provision existing traffic. In this work, we investigate how to selectively re-provision connections from C band to L band during a batch upgrade. This is to ensure greater availability of C-band resources which can help to delay network upgrade and hence reduce upgrade cost, while limiting the number of disrupted connections in the network. This study proposes two re-provisioning strategies, namely, Budget-Based (BB) and Margin-Aware (MA) re-provisioning, which rely on the Quality of Transmission (QoT) of lightpaths. These strategies leverage the knowledge of Generalized Signal-to-Noise Ratio (GSNR) to choose which lightpaths to re-provision. We compare these strategies with a baseline distance-based strategy that uses path length to select and re-provision lightpaths. We also incorporate Machine Learning techniques for QoT estimation of lightpaths to reduce the computational time required for optical-path feasibility check. Numerical results show that, compared to distance-based strategy, BB and MA strategies reduce disruption by about 22% and 27%, respectively, in representative network topologies. 

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

   https://doi.org/10.23919/ONDM65745.2025.11029221  

   Gao, Ruoxuan; Kalkunte, Ramanuja; Abkenar, Forough Shirin; Ferdousi, Sifat; Ibrahimi, Mëmëdhe; Tornatore, Massimo; Mukherjee, Biswanath (May 2025, IEEE)

   Not AvailableNetwork 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%. 

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3. An Effective Strategy for Link Upgrade from C to C+L Band in Elastic Optical Backbone Networks

   https://doi.org/10.1109/ANTS59832.2023.10469649  

   Kalkunte, Ramanuja; Abkenar, Forough Shirin; Jana, Rana Kumar; Aureli, Davide; Ferdousi, Sifat; Srivastava, Anand; Mitra, Abhijit; Tornatore, Massimo; Mukherjee, Biswanath (December 2023, IEEE)

   Multi-band transmission is a promising solution for capacity enhancement in optical networks. We propose a novel strategy, named C to C+L Upgrade (CLU), to gradually upgrade links from C to C+L bands. We develop a Recurrent Neural Network (RNN)-based model to efficiently predict links for upgrade, based on network state and resource utilization, to reduce blocking and upgrade cost. Our results show that CLU outperforms baseline strategies (which do not employ predictive decisions) by upgrading fewer links at appropriate times. 

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4. C+L-band upgrade strategies to sustain traffic growth in optical backbone networks

   https://doi.org/10.1364/JOCN.427097  

   Ahmed, Tanjila; Mitra, Abhijit; Rahman, Sabidur; Tornatore, Massimo; Lord, Andrew; Mukherjee, Biswanath (June 2021, Journal of Optical Communications and Networking)

   We investigate cost-efficient upgrade strategies for capacity enhancement in optical backbone networks enabled by C+L-band optical line systems. A multi-period strategy for upgrading network links from the C band to the C+L band is proposed, ensuring physical-layer awareness, cost effectiveness, and less than 0.1% blocking. Results indicate that the performance of an upgrade strategy depends on efficient selection of the sequence of links to be upgraded and on the time instant to upgrade, which are either topology or traffic dependent. Given a network topology, a set of traffic demands, and growth projections, our illustrative numerical results show that a well-devised upgrade strategy can achieve superior cost efficiency during the capacity upgrade to C+L enhancement. 

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5. A Comparative Analysis of Multi-Band Upgrade and Regeneration for Capacity Enhancement in Optical Networks

   Gao, R; Ferdousi, S; Tornatore, M; Mukherjee, B (December 2025, IEEE)

   This paper explores the joint impact of two capacity enhancement schemes in optical backbone networks: multi-band expansion from C+L to C+L+S bands and varying 3R regeneration (no, selective, and full). Using a pay-as-you-grow batch upgrade framework that considers deferral benefits, we evaluate their interaction. In the short-haul BT-UK network, S-band upgrade consistently improves throughput and cost efficiency, with the greatest economic gain with no regeneration. In the long-haul USNET network, S-band upgrade reduces throughput because K-least-loaded routing does not consider path distance, yielding low-quality lightpaths with high blocking probability. Thus, C+L bands with full regeneration are more cost-effective. 

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