Distributed Fiber Sensing (DFS) leverages optical backscattering signals to predict failure events and enable just-in-time restoration in metropolitan optical networks, i.e., without optical amplifiers. In this paper, we study the effectiveness of proactive restoration based on DFS information in all-optical networks, while considering different sensing devices' capabilities. We evaluate whether restoration can be provisioned just-in-time before a failure happens, and its impact on key performance metrics, including the number of affected and suspended optical circuits, bandwidth blocking rate, and service downtime. Simulation results demonstrate that just-in-time restoration enabled by DFS with a prediction time capability of 15~ms can reduce circuit disruptions by more than 90\% compared to restoration without sensing and ensure optical service continuity in optical networks comparable to resource-intensive protection schemes, at a fraction of the spectral resources.

The next-generation mobile networks follow the 3GPP disaggregated Radio Access Network (RAN) model, composed of three separate functional units: Centralized Unit (CU), Distributed Unit (DU), and Radio Unit (RU), and its interconnection network infrastructures, front-haul, between RU and DU and mid-haul, between DU and CU. The current focus has been extensively on the front-haul, proposing a myriad of networking technologies and resource allocation solutions. Mid-haul transport infrastructure has received comparably less attention. This paper explores the implementation and performance of optical multi-flow transponders in mobile mid-haul networks. It evaluates the performance of mid-haul mesh topologies with different DU placement methods. Numerical results show the achievable throughput and blocking performance. We also derive the number of Multi-flow optical transponders (MOTP) units deployed, as well as the related trade-offs.

Campus networks are expected to include various new features compared to 4G and 5G networks, such as the exploitation of THz frequency bands and real-time network optimization. Furthermore, to enable future-proof network control, the Digital Twin Network (DTN) reference architecture can be exploited to create an autonomic network system that provides intent-based interfaces and offers a complete adaptive network control tailored for campus network applications. This paper discusses such architecture and presents a case study focused on a THz system that can adapt its coding and modulation parameters in response to channel degradation due to environmental changes. Finally, simulation results evince the advantages of the proposed architecture.

Spatially multiplexed networks have become one of the prime technology candidates to accommodate the unstoppable network traffic increase. Currently, two core-switching approaches are under consideration in the research community: full and restricted. In full core-switching optical network, the switching flexibility is maximal with the full port capacity and comparably larger equipment cost. In restricted switching, on the other hand, the equipment is simpler and less costly, but the wavelength circuit needs to remain in the same core along the route. We propose the study a combination of the two, which we refer to as sparse core-switching as tradeoff between the core-switching capabilities and the cost of capacity applied to the network. We are especially interested in physical layer aspects in the context of crosstalk and the resulting spectrum fragmentation and in understanding how crosstalk impact the performance of sparse core switching. Numerical results show that with the proper application of a fraction of the equipment budget required for the full-switching scenario, sparse core switching reaches an average performance gain of 31.34% and a cost reduction of 71.2 % and thus can even outperform the full-switching scenario.

In Elastic Optical Networks (EON), the literature usually measures QoT (Quality of Transmission) by the Optical Signal-to-Noise Ratio (OSNR) or estimated maximum transparent reach of the modulation technique adopted by the circuit. This paper evaluates the Quality of Transmission (QoT) margins adopted in traditional Routing, Modulation Level, and Spectrum Assignment (RMLSA) algorithms that quantity QoT through the maximum transparent reach of the modulation techniques. A RMLSA algorithm is proposed that categorizes the minimum margins that must be adopted for the establishment of new circuits, based on their expected degeneration and the impact it will have on the already established optical circuits. Simulation results show that the proposed minimum margins associated with circuit invigoration present better results than algorithms that propose a fairer margin or evaluate QoT through the maximum transparent reach. The proposal showed a reduction of up to 89% of bandwidth blocking rate and with a runtime performance similar to the simpler algorithms that evaluate QoT by distance.

The emergence of Elastic Optical Networks (EON) has brought new conceptions in the operations of optical networks, improving its flexibility and efficiency. The routing and spectrum assignment (RSA) is one of the key problems in EON which deals with resource allocation. In order to reduce the bandwidth blocking ratio on the network, recently, Auxiliary-Graph-Model approaches propose spectrum reservation schemes to reduce the network exhaustion probability. However, these approaches do not take into account the energy expenditure caused by these schemes. In this work, we use an auxiliary graph model to design a new RSA heuristic algorithm to improve the network energy consumption without losses in bandwidth blocking rate. Numerical results show that our proposal may provide a reduction of up to 54% in the bandwidth blocking ratio and achieve a gain of up to 51% in energy efficiency compared to literature.

Despite the research advances in intra-domain light-path provisioning in WDM networks, efficient and practical schemes for path computation and resource advertisement in multi-domain mesh networks still need to be developed. Most of the proposed solutions in the literature lacks the ability to convey optical network-specific Traffic Engineering information and are based on periodic message flooding technique. The solution presented in [1] achieved better performance than those based on periodic flooding while performing domain chain computation. However, it relies on potentially outdated routing information which can increase blocking of requests for lightpath establishment. The solution proposed in this paper considers the effective wavelength availability during path computation and adopts a destination-driven wavelength assignment scheme.

Despite the research advances in intra-domain light-path provisioning in WDM networks, efficient and practical schemes for path computation and resource advertisement in multi-domain mesh networks still need to be developed. Most of the proposed solutions in the literature lacks the ability to convey optical network-specific Traffic Engineering information and are based on periodic message flooding technique. The proposed solution provides a novel and economical way to disseminate information while performing the domain chain computation. It also provides a policy-based wavelength selection scheme that allows a load balanced provisioning of end-to-end lightpaths.

Optical networks can benefit from multipath routing by routing traffic over diverse fiber links to fulfill bandwidth requirements, balance network load and improve resource utilization. This paper focuses on the effectiveness of multipath routing on aggregating residual bandwidth of the established lightpaths using dynamic traffic grooming. An optimization model based on Integer Linear Programing (ILP) is formulated to leverage multipath routing and grooming to serve connection requests with known duration, in a scenario where the dynamic traffic can demand bandwidth either larger or smaller than a single wavelength capacity. The impact of a balancing policy, referred to as Holding Time Balancing (HTBalancing), on multipath routing with traffic grooming in optical networks is also investigated. Numerical results show that the proposed optimization model can achieve a lower bandwidth blocking and a better load balancing with HTBalancing policy, when compared with single path routing. The proposed relaxation algorithm can effectively find near optimal solutions, and be applied in realistic scenarios.

In this paper, a new algorithm for dynamic traffic grooming is introduced. It considers the holding-time of the connections and it aims at balancing the load among existing lightpaths to avoid the formation of bottlenecks and, consequently, high blocking probability values. Results indicate that it produces significantly lower blocking probabilities when compared to other holding-time-aware algorithm. Moreover, it promotes a fair distribution of blocking among source-destination pairs.

Dynamic grooming deals with requests for wavelength allocation based on a dynamic pattern of arrivals in contrast to the situation of static grooming in which the pattern of arrivals must be previously known. Solutions for dynamic grooming typically involve the construction of an auxiliary graph for deciding on the routing and wavelength assignment. An auxiliary graph can represent the network either entirely or partially. The complexity of grooming algorithms is significantly reduced when a partial representation of the network is employed. Algorithms that employ reduced auxiliary graph have a step for the expansion of such graphs in case paths are note found for lightpath establishment. Results reveal that the expansion mechanism can be reduced or even eliminated for reducing the complexity of the algorithms without compromising significantly the performance of the algorithms, especially under high load.

Traditional protection schemes guarantees 100% reliability in case of single link failure which demands resources while differentiated reliability provides a granular protection scheme. Moreover, if the signal quality in a path is below acceptable values, a path cannot be used by incoming requests for lightpath establishment. Therefore, the signal quality needs to be checked by the routing and wavelength assignment algorithm (RWA). This paper investigates shared path protection with differentiated reliability taking into account the PMD and the ASE impairments in path selection. The efficacy of the algorithm proposed is compared to that of its impairment unaware counterpart.

In this paper, we propose to apply multipath routing in optical networks for the emerging high-performance applications with extremely high bandwidth requirements, typically larger than the capacity of one wavelength. To this end, we present a novel Multipath lightpath Provisioning mechanism and derive an optimal solution by an ILP (Integer Linear Programming) approach, with differential delay and bandwidth as constraints to multipath finding. Our mechanism can set up multiple lightpaths over multiple fiber-level paths not only to satisfy the extremely high bandwidth requirements, but also to reduce the minimum bandwidth required for backup paths as it reduces the amount of traffic affected by single fiber breaks. For comparison, we also present an ILP-based Single Path Lightpath Provisioning mechanism and show that its multipath counterpart performs better independently of the mesh topology under study. The performance results demonstrate that the proposed multipath lightpath provisioning mechanism outperforms the traditional single path routing by decreased bandwidth request blocking ratio, while reducing the amount of traffic that may be affected by single link failures.

Traffic grooming in wavelength division multiplexing networks merges low-speed flows into large capacity pipes so that the bandwidth discrepancy between them will not lead to underutilization of resources. Dynamic grooming deals with requests for wavelength allocation based on a dynamic pattern of arrivals in contrast to the situation of static grooming in which the pattern of arrivals must be previously known. Solutions for dynamic grooming typically involve the construction of an auxiliary graph for deciding on the routing and wavelength assignment. An auxiliary graph can represent the network partially leading to scalable solutions, although blocking is not fairly distributed among calls in such solutions. A novel algorithm is thus proposed for achieving fairness in blocking among the calls. In an off-line step, it defines an appropriate set of OXCs for achieving fairness and efficient use of resources. Results reveal a higher degree of fairness obtained by the use of the novel algorithm than for previously proposed algorithms.

Traffic grooming in wavelength division multiplexing networks merges low-speed flows into large capacity pipes so that the bandwidth discrepancy between them will not lead to underutilization of resources. On-line solutions for dynamic grooming typically involve the construction of an auxiliary graph for deciding on the routing and wavelength assignment. An auxiliary graph can represent the network partially leading to scalable solutions. Previous algorithms based on such type of auxiliary graph produce unfair distribution of resources. This paper introduces a novel algorithm and two of its variants, which are scalable and produce low blocking and fair distribution of resources.

In wavelength division multiplexing (WDM) networks, failures can imply in great loss of data due to high transmission rates, leading to the need of employment of protection mechanisms. Transparency and switching in all-optical networks causes physical impairments, which can significantly degrade the signal quality. If the signal quality in a path is below acceptable values, this path cannot be used by incoming requests for lightpath establishment. Therefore, quality needs to be checked by the routing and wavelength assignment algorithm. This paper introduces two novel algorithms for shared path protection in WDM networks that take into account the PMD, ASE and homowavelength crosstalk physical impairments in path selection. The efficacy of these algorithms are compared to those of their impairment unaware counterpart.

The assignment of wavelengths to lightpaths in WDM networks is a crucial problem that needs to be solved efficiently. However, the coloring of the graph representing the lightpaths and their interference is an NP-hard problem. The parameterized Complexity Theory offers an attractive theoretical framework for the derivation of exact solutions with lower complexity than those derived using the Classical Complexity Theory since it transfers the exponentiality dependence from the input parameters describing the network to a parameter called modulator which can be bounded. This paper presents an algorithm for wavelength assignment in transparent WDM networks. Numerical examples illustrate the benefits of the employment of this new theory for the solution of the wavelength assignment problem.

The ability to cope with dynamic bandwidth demands will be a particularly important asset for Quality of Service provisioning in networks carrying bandwidth hungry applications. This paper introduces a novel approach based on multi-objective optimization with fuzzy constraints for dynamic bandwidth allocation. This new approach deals with uncertain bandwidth demands more efficiently than an approach based on Classical Optimization Theory and yet supports Quality of Service commitments.