This special issue features the extended versions of selected papers presented at the 25th International Conference on Optical Network Design and Modeling (ONDM 2021), which took place virtually from 28 June through 1 July 2021. The conference traditionally addresses cutting-edge research in established areas of optical networking and their adoption in support of a wide variety of new services and applications. This includes the most recent trends such as 5G and beyond; data-center networking; Internet of Things; cloud/edge computing; content delivery; big data, data analytics, network telemetry, and real-time monitoring; autonomic networking; artificial intelligence/machine learning assisted networks; visible light networks; and quantum secured networks. The program featured 33 contributed papers and 9 posters, as well as 3 keynotes, 15 invited talks, and 3 tutorials.

The papers included in this special issue outline the current trends in optical networking research, ranging from transmission parameter optimization for enhanced network performance and evaluation of spectral efficiency in multicore fibers, over multilayer optimization in point-to-multipoint coherent systems, to blockchain-based distributed marketplaces enabling trusted network sharing.

Transmission optimization for ultra-wideband systems

The growth of the carried data traffic forces continuous upgrade of the transmission capabilities. One solution to increase fiber capacity is ultra-wideband transmission (UWB) covering the $\text{S}+\text{C}+\text{L}$ bands. Signals in UWB transmission systems can be significantly affected by nonlinear effects like the inter-channel stimulated Raman scattering (ISRS), where signal power is transferred from short to long wavelengths. To maximize the system throughput, various signal and system parameters must be carefully set.

The paper “On the impact of launch power optimization and transceiver noise on the performance of ultra-wideband transmission systems” by H. Buglia et al. addresses the UWB transmission system parameter optimization to maximize the system throughput. Theoretical modeling and experiments investigate the transceiver noise and launch power in the 1485–1620 nm band. The paper shows that, for shorter distances, the transceiver noise reduces gains achieved by the launch power optimization in the presence of ISRS. This indicates the need to consider transceiver noise when designing and modeling the UWB transmission systems.

Probabilistic constellation shaping in multicore fiber networks

Future optical core networks are envisioned to increase their capacity by combining Flex Grid, spatial division multiplexing (SDM), and multicore fibers (e.g., MCF, FM-MCF). Strategies for improving the performance of those networks are typically aimed at selecting the modulation format based on the network capacity and transmission distance. A recent approach referred to as probabilistic constellation shaping (PCS) aims to find a compromise between spectral efficiency (SE) and transmission distance. PCS has been shown to achieve SE closer to the Shannon’s limit and good results in standard fiber.

In the paper “Evaluation of probabilistic constellation shaping performance in Flex Grid over multicore fiber dynamic optical backbone networks” by Jordi Perelló et al., the authors investigate the potential benefits stemming from the adoption of PCS in future Flex Grid/MCF optical networks. The authors propose a worst-case methodology for estimating the attainable SE along pre-computed paths in Flex Grid/MCF optical networks, accounting for both bypass and add/drop losses at SDM-ROADMs. After defining the maximum SE (b/s/Hz), two route, modulation format, core and spectrum assignment heuristics are introduced for more cost-effective SDM-ROADM design by PCS compared to traditional solutions.

Point-to-multipoint coherent optics for multilayer optimization

The continued growth in traffic and capacity requirements drives the operators’ need to further reduce the cost per transported bit. Point-to-multipoint (P2MP) coherent optics using digital subcarrier multiplexing (DSCM) was recently proposed as a promising technology to lower the cost and complexity of optical transport networks, particularly in metro scenarios with hub-and-spoke (H&S) traffic patterns. Since this technology has been developed only recently, the cost savings of P2MP optical architectures using DSCM still need to be thoroughly assessed.

The paper “On the benefits of point-to-multipoint coherent optics for multilayer capacity planning in ring networks with varying traffic profiles” by Pablo Pavon-Marino et al. assesses the benefits of P2MP using DSCM solutions in metro network scenarios. They propose mixed integer linear programming formulations for multilayer capacity planning to minimize the total transceiver costs, considering both point-to-point and P2MP transceivers. The results indicate that P2MP optics bring transceiver cost savings, especially at high network loads and for traffic patterns that are mostly H&S. They also found that P2MP optics using DSCM trigger a redesign of the multilayer network resulting in a significantly reduced spectrum usage and a lower number of IP hops. As a result, operators embracing this technology can expect a reduced optical-electronic-optical and IP processing latency and lower IP layer equipment costs.

Trusted sharing of virtual passive optical networks

The 5G evolution thrusts forward various resource-demanding services, calling for extensive sharing of the common physical infrastructure, particularly in the access segment that is typically realized by passive optical networks (PONs). The proliferating paradigm of network function virtualization offers a tool for creating new business opportunities and models that challenge conventional centralized network ownership. The new PON infrastructure sharing model requires incentives for operators to honestly participate in resource sharing.

The paper “Trusted distributed marketplace for virtual passive optical network sharing” by Nima Afraz and Marco Ruffini proposes a framework for dynamic auctioning of PON transmission capacity, with the aim to incentivize trusted network sharing among competing virtual network operators that cooperate over the same physical PON infrastructure. The solution relies on decentralizing the market mechanism using blockchain technology, where the smart contract will assure that all stakeholders can verify the previous transactions and, thus, provide a transparent and automatically enforced market logic that can operate without reliance on a trusted third party. The feasibility and performance of the proposed verification layer are assessed through a newly developed smart contract that uses the Hyperledger Fabric permissioned blockchain platform to solve the high transaction cost and energy consumption concerns associated with permissionless blockchain solutions.

We hope that this special issue will enlighten the JOCN readership on the exciting trends in optical networking and inspire new research efforts. We thank the authors for extending their work and preparing the papers sometimes under challenging circumstances, as well as the expert reviewers for their detailed feedback. We are grateful to the past Editor-in-Chief Jane M. Simmons, who proposed and supported this special issue, as well as the interim EiC Pat Iannone, the new EiC Andrew Lord, and the JOCN Staff for their continuous support during the sad and challenging transition period. Finally, we would like to dedicate this special issue to the memory of Jane M. Simmons.

Guest Editors:

Marija Furdek,

Chalmers University of Technology, Sweden,

Lead Guest Editor

Paolo Monti,

Chalmers University of Technology, Sweden

Carmen Mas Machuca

Technical University of Munich, Germany

Jarosław Turkiewicz,

Warsaw University of Technology, Poland

David Larrabeiti,

University Carlos III of Madrid, Spain