The rapid increase in channel spectral width is outpacing the available spectrum of deployed fibers, leading to accelerated capacity exhaustion in meshed core networks. This paper addresses this critical issue by proposing the use of advanced optical interfaces that enable the selective allocation of digital subcarriers (multi-carrier transceivers). By leveraging these interfaces, the spectral efficiency of core networks can be significantly enhanced, thereby ensuring more efficient utilization of the existing fiber infrastructure and extending the lifespan of current fiber deployments. Results comparing the utilization of multi-carrier transceivers versus traditional single -carrier transceivers show that the former can significantly increase usable network capacity without increasing transceiver count. This advantage is especially evident at higher symbol rates, where fewer channels per fiber result in faster spectrum exhaustion.

In multi-band networks, the problem of power transients due to spectral loading changes (due to link failures and/or channel add/drop) can have considerable impact on surviving traffic relative to standard C-band operation, due to the increased impact of stimulated Raman scattering (SRS) effects between co-transmitted bands. In this paper, we evaluate how selectively assigning spectrum in the C - and L-bands according the potential failure profiles in the network can help reduce the average and worst-case effect of power transients due to loading changes. This type of strategy also presents an intricate trade-off, since better transient resiliency allows channels to operate with lower margins (and thus with higher modulation formats), but on the other hand a transient minimization spectrum assignment may lead to increased fragmentation. The comparison will help identify in which types of networks and traffic use-cases these specialized spectrum assignment techniques are most promising.

Routing and Spectrum Assignment (RSA) is key to an efficient resource usage in optical networks. Although this problem is known to be complex, an even more complex version arises when considering multi-band (MB) optical networks, where the spectrum-dependency of performance becomes significantly more pronounced. This paper proposes a Deep Reinforcement Learning (DRL)-based strategy for RSA in MB optical networks leveraging the GNPy library for accurate estimation of optical performance. Simulation results show that DRL-RSA reduces blocking by up to 80% when comparing to state-of-the-art RSA strategies.

We study the consequences of power transients caused by link faults and stimulated Raman scattering in multi-band networks. Results show that carefully optimizing transient margins should avoid high capacity reduction and excessive costs.

We evaluate survivable network design options in the scope of C+L long-haul systems with high baud-rate channels. The analysis shows how design margins required for different failure response levels significantly affect resource and cost efficiency.

Routing and spectrum assignment strategies exploiting Reinforcement Learning are investigated for multi-band optical networks. Generalized Signal to Noise Ratio accounting for Stimulated Raman Scattering is estimated driving modulation format selection. Simulations show that RL may reduce the blocking probability by one order of magnitude.

A routing and spectrum assignment strategy based on Reinforcement Learning (RL-RSA) is proposed for multi-band optical networks. RL-RSA accounts for Stimulated Raman Scattering using the Generalized Gaussian Noise model. Simulation results show that RL-RSA increases the throughput by 20%.

—This paper investigates the suitability of small and unamplified multicast switches to cost-effectively realize highly flexible optical transport networks. A comprehensive modelling exercise considering four possible generations of line interfaces, operating at increasingly higher symbol rates, is reported. The simulation results obtained over a reference network topology provide evidence that small and unamplified multicast switches will have little to no effect in limiting the usable network capacity and, as a result, can be exploited to design lower cost contentionless architectures in next-generation optical networks exploiting C- or SuperC-band fiber transmission.

This paper analyzes how the next-generation of coherent optical interfaces for transport networks, based either on pluggable or high-end transponder modules, perform when required to provide traditional layer-0 protection/restoration mechanisms used in these scenarios. While the typical trade-off between these different devices lies in the capacity and reach vs. cost/complexity, survivability methods add further dimensions to the problem. Specifically, line-side protection methods have more stringent performance requirements due to the need to support both the working and protection paths with the same channel format. Optical restoration allows both backup spectrum and regenerators to be shared, which coupled to a much wider array of possible transmission formats leads to nontrivial design solutions for a given planning instance. In this analysis, we leverage a thorough optical performance characterization of pluggable and high-end interfaces, accounting for various realistic impairments, and combine it with an Integer Linear Programming (ILP) model that optimizes optical interface count in network designs with both line-side path protection and shared restoration. The results highlight, for different topology and traffic requirements, how deploying optical protection benefits from having more granular channel formats to choose from with high-end coherent. Optical restoration with backup regenerator placement optimized for sharing is also shown to be critical in making pluggable interfaces more competitive in larger topologies.

The combination of traditional optical transport network paradigms with the advent and necessities of edge computing opens up new challenges for optimizing both the optical layer and the data-center (DC) infrastructure. In the specific case of ring/horseshoe metro access topologies, the flexibility to divert services to a specific DC with low latency is highly dependent on the node architecture that is employed. Consequently, the optimal trade-off between consolidating services in larger DCs and the number of transponders required for transporting traffic will shift depending on the possibilities enabled by the network itself. Furthermore, traditional north/south traffic to/from the core is still expected to be significant in these topologies, providing opportunities to leverage existing optical bandwidth for improved cost effectiveness. This process requires a careful dimensioning in order to optimally consider all impacting factors and select which services to assign where. We model this problem with a mixed integer quadratically constrained problem (MIQCP) that optimizes DC resources for a given availability level according to services' mean and peak loads. This optimization accounts for the interdependencies with the required optical transponder costs and the constraints imposed by service latency, as well as the specific restrictions imposed by optical nodes based on fixed/reconfigurable add/drops, or filterless solutions. The resulting analysis not only provides optimal solutions to specific network/DC planning instances, but also identifies general deployment guidelines for metro access networks in terms of desired node architectures for each network scenario.

We investigate capacity upgrade of metro networks using differentiated node architectures for C+L-bands. The combination of experimental results and network simulations highlights scenarios where low-cost unamplified L-band extensions can be leveraged for maximum capacity.

This paper introduces a novel and simplified cost model for designing and evaluating a Central Office Rearchitected as a Datacenter (CORD). The model includes equipment and elements for the realization of optical, packet switching, and data center parts with a special focus not only on relative costs but also on power consumption figures. The cost model is then applied to the design and comparison of a metropolitan area network (MAN) including both aggregation and metrocore nodes following several MAN node architectures based on CORD-like leaf-and-spine fabric. In particular, equipment disaggregation at the Central Offices, both on the packet-switching and optical components, can provide important cost savings to telco operators. On the other hand, incorporating computing/storage capabilities in the MAN for the realization of multiaccess edge computing (MEC) has a significant impact on the total network cost but especially on power consumption.

The concept of edge computing is vital in the 5G ecosystem, as a means of introducing application awareness in the network and enabling constructs such as slicing to be effectively implemented. In this scope, an efficient infrastructure dimensioning requires visibility of both network and data-center resources. While this joint optimization is becoming increasingly common even at the optical layer, some aspects of the dimensioning remain siloed between the network/IT worlds. Survivability mechanisms are one such example, where protection for lightpaths and/or virtual network functions (VNFs) is typically provisioned independently, potentially incurring in resource overprovisioning. This paper investigates the merits of exploiting a hybrid strategy where backup resources are selectively distributed between the IT and optical layers in metro ring scenarios, according to specific service requirements such as latency and bandwidth. Critically, this analysis incorporates, through an integer linear programming (ILP) model, the effect of optical path performance on the cost efficiency of protection mechanisms, which is shown to greatly influence the optimal resource distribution in each deployment scenario.

Optical transport networks are progressively being designed around reconfigurability. Operators require an infrastructure capable of carrying large amounts of data, but also able to deliver that data when and where needed. While centralized control plane architectures based on software-defined networking are pushing flexibility in automation and interoperability, many of these objectives are reliant on a hardware-enabled flexible data plane. At the same time, reduced operating margins imply that capacity planning through resource overprovisioning is increasingly unsustainable. Therefore, a natural tradeoff between cost and flexibility emerges in many aspects of optical transport network architectures. More complex and reconfigurable hardware, such as flexible-rate transponders or switching fabrics, can be pitted against cheaper purpose-built modules as contending alternatives for incrementally deploying networks. The added value of adaptability to changing conditions must be evaluated against its potential upfront cost and capacity overprovisioning risk. In this context, technoeconomic analysis based on multiperiod capacity optimization plays a pivotal role in identifying the target network scenarios for fixed and flexible hardware. In this paper, use cases where the cost/flexibility tradeoff emerges in optical transport scenarios are identified, such as in the design of line cards and multilayer grooming architectures, and multiperiod optimization frameworks based on integer linear programming (ILP) models are presented. More generally, this paper also discusses scalability issues affecting the use of ILPs for multiperiod capacity optimization, and proposes some simple design and modeling guidelines to help overcome them. These include either reformulating the models themselves, or identifying specific subproblems within the global framework that can be offloaded without undermining the validity of the results.

We evaluate a service provisioning mechanism to strike a balance between overly pessimistic/optimistic in-band crosstalk penalty estimation in meshed networks. Simulations show that optimizing in-band crosstalk margins according to the topology and routing pattern can help extend capacity for lower-cost networks with high nodal degrees.

High baud rate channels present a significant problem in large scale high degree count metro core networks. We consider deployment strategies specifically optimized for flex-grid to overcome traditional approaches with 6.25GHz granularity.

The recent interest in the upgrade and enhancements of metro transport networks and the availability of transponder cards with coherent receivers is opening the way to filterless solutions employing only passive splitters/couplers and optical amplifiers, potentially achieving significant capital expeditures and operating expenditures savings. However, the filterless option suffers from inefficiencies, mainly due to the broadcasting constraint and the reduced optical reach. To overcome such limitations, this paper proposes three complementary strategies to upgrade optical filterless metro networks (FMN). First, the number of supported channels is incremented by exploiting the full C + L -band. To this end, two design architectures (i.e., Single and Dual Region) are proposed and evaluated, targeting double capacity with respect to the standard C-band and an upgrade to cost reduction. Second, we investigate a dual-architecture solution, extending metro deployments with a low-cost filterless and unamplified L-band system. Its design trade-offs are evaluated to determine its suitability in providing direct low-latency connectivity between metro-access nodes with the aim of supporting edge-computing platforms. Finally, the flexibility of the FMN is extended by introducing disaggregated transponders with different bitrates (i.e., 100 Gbps and 400 Gbps) and configurable transmission parameters, such as the modulation format and the forward error correction). Such flexibility is exploited through the extension of the OpenConfig YANG model of the optical line system, thus enabling automatic spectrum and transmission parameter assignment by means of a centralized software-defined-network controller and achieving better resource utilization. Simulation and experimental results are provided, showing the effectiveness and the potential impact of filterless metro solutions in future deployments and low-cost network upgrades supporting edge/fog clusters and 5G.

The convergence of optical metro networks with small data-centers at the edge is reshaping how optical nodes and networks are architected. This paper explores the architecture of the metro aggregation node and its effect on edge data-center dimensioning requirements. Through network simulation on a wide range of chain topologies and load profiles, we evaluate the extent to which direct lightpaths between aggregation nodes can be used to load balance server utilization. This enables to understand how optical layer flexibility interworks with service bandwidth and latency requirements to shape the best trade-offs between server, line system and transponder costs.