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In this article, we focus on the design of different node architectures suitable for few-mode multi-core fibers (FMMCFs) based networks. Both dimensions, core and mode, open different possible ways to group spatial channels depending on the physical impairments of the space-division multiplexed (SDM) optical fibers. Moreover, the channel switching across a group of cores/modes at once and the end-to-end routing are not only mandatory aspects for certain spatial channels, but also recommendable in order to reduce the node complexity/cost. Thus, we propose various SDM-capable node architectures based on versatile and homogeneous spatial group configurations. Then, a unified physical-layer-aware Quality of Transmission (QoT) estimator is formulated to not only evaluate these node architectures in a simulation tool, but also validate them in a real experimental environment using a stateful path computation element (PCE) as a central controller. The obtained results disclose that the cost-efficient node design parameter, namely, the size of the spatial group G, depends on both the network and traffic profile size. Specifically, for a national optical backbone network equipped with a homogeneous and hexagonally arranged 6-weakly-coupled modes and 7-weakly-coupled cores fibers, G equals 6, while for a continental backbone network, G can raise up to 14. In any case, we demonstrate that the cost-benefit tradeoff in node design must be analyzed in detail in order to meet the huge traffic volumes of the next years. This work was supported by the Spanish Project AURORAS under Grant RTI2018-099178-B-I00.

Future optical core networks realizing Flex-Grid and Space Division Multiplexing (Flex-Grid/SDM) will be key to effectively cope with the rapid growth of the Internet traffic, thanks to their superior capacity and spectrum utilization flexibility. Specifically about SDM, the spatial dimension can be considered either fixed or flexible. The goal of this work is two-fold. Firstly, it aims at quantifying the capacity (in terms of throughput) of Flex-Grid/SDM networks assuming either a fixed or a flexible spatial dimension. To this end, we scale up the spatial multiplicity from 7 to 30 spatial channels, considering Multi-Fiber (MF) and Multi-Core Fiber (MCF) solutions. Secondly, it also aims at analyzing the throughput scalability in these networks versus their hardware requirements, especially from the transponder requirements point of view. The obtained results show that, for a 4.3× spatial multiplicity scaling factor, the throughput of spatially fixed Flex-Grid/SDM networks scales up to 3.5×. Conversely, when the spatial dimension is considered flexible, throughput can be pushed up to a 5× factor for both MF and MCF solutions. However, a long-term realization of spectrally-spatially flexible optical networks (SS-FONs) requires up to 9.6× more laser sources and 2.7× electronic complexity (per required connection) in the transponders compared to spatially fixed Flex-Grid/SDM networks. Furthermore, SS-FONs enable different options for assigning the spectral and spatial resources to traffic demands. In this sense, another contribution of this work is the introduction of a novel methodology that trades network throughput for transponder (the major network equipment cost in SDM networks) complexity reduction.

In this paper, we target an optimal multiple-input multiple-output digital signal processing (MIMO-DSP) assignment to super-channels affected by intercore crosstalk (ICXT) in multicore fiber (MCF) enabled transparent optical core networks. MIMO-DSP undoes ICXT effects, but can be costly with high core density MCFs. Hence, its implementation in the network must be carefully decided. We address our objective as a joint route, modulation format, MIMO and spectrum assignment (RMMSA) problem, for which integer linear programming formulations are provided to optimally solve it in small network scenarios. Moreover, several heuristic approaches are also proposed to solve large-scale problem instances with good accuracy. Their goal is to minimize both network spectral requirements and the amount of MIMO equalized super-channels, taking a crosstalk-free space division multiplexing (SDM) solution as a reference, for example, based on parallel single mode fibers [i.e., a multifiber (MF) scenario]. For our evaluation, we consider several state-of-the-art MCF prototypes and different network topologies. The obtained results, with the considered MCFs, disclose that in national backbone networks, the desirable percentage of super-channels with MIMO equalization to match the performance of an equivalent crosstalk-free SDM solution ranges from 0% to 36, while in continental-wide networks this range raises from 0% to 56%. In addition, in the case of a nonideal MIMO (with a 3 dB/km of crosstalk compensation), such percentages range from 0% to 28% and from 0% to 45% in national and continental-wide backbone networks, respectively, experimenting a performance gap up to 12% with respect to the MF reference scenario.

Space Division Multiplexing (SDM) appears as a promising solution to overcome the capacity limits of single-mode optical fibers. In Flex-Grid/SDM optical networks, nodes offering full interconnection between input/output fiber ports and spatial channels, typical SDM-Reconfigurable Optical Add/Drop Multiplexer (SDM-ROADM) referred to as independent switching with lane support (InS with LC support), require very complex and expensive node architectures. Alternative designs have been proposed to relax their requirements, such as those realizing Joint-switching (JoS) by switching one spectrum slice across all spatial channels at once. In this work, we evaluate the benefits of a cost-effective SDM-ROADM architecture that makes a trade-off between (i) performance in terms of network throughput and (ii) architectural complexity by forcing the Space Continuity Constraint (SCC) end-to-end, that is, along the connection physical path. The performance and architectural complexity of such a SDM-ROADM solution are compared in dynamic Flex-Grid/SDM scenarios against benchmark networks based on InS with LC support and JoS SDM-ROADMs, under both spatial and spectral super-channels. We quantify the network throughput when scaling the spatial multiplicity from 7 to 30 spatial channels, considering Multi-Fiber (MF) as well as Multi-Core Fiber (MCF) SDM solutions. The obtained results reveal that differences in terms of network throughput employing InS without LC support SDM-ROADMs is merely up to 14% lower than InS with LC support SDM-ROADMs, while the network CAPEX can be dramatically reduced by 86%. In contrast, networks employing InS without LC support SDM-ROADMs carry up to 40% higher throughput than JoS ones, whereas the network CAPEX can be raised up to 3×. This paper also analyses the spatial multiplicity impact on both network metrics (throughput and CAPEX).

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works This article identifies the unavoidably required upgrade of short-term realizable elastic optical networks (EONs) operating over single-mode fibers toward spectrally-spatially flexible optical networks (SS-FONs), exploiting spatial division multiplexing (SDM) technology in order to cope with the expected mid- and long-term future traffic forecasts. Since a complete EON to SS-FON network migration overnight is unrealistic, this article proposes a gradual greenfield migration strategy employing novel heuristic planning solutions. These solutions allow identifying which network components should be SDM-capable so as to support the forecasted traffic increase at a given time. To allow transmission in an SS-FON, links should be extended with SDM-capable fibers and nodes should be equipped with SDM-capable reconfigurable optical add/drop multiplexers. Using the proposed solutions, a migration case study in a national reference core network is provided and analyzed.

In this paper, we evaluate in a network planning scenario the performance of typical Wavelength Division Multiplexing (WDM) networks versus networks based on flexible spectrum grid (i.e., Flex-Grid networks). To this end, we propose several lightweight heuristics with adaptive routing strategies and a Simulated Annealing (SA)-based metaheuristic in order to minimize the spectrum occupation. Moreover, we use the CEDIA backbone network under realistic traffic scenarios. The results obtained with the most promising heuristic disclose that, for foreseeable traffic conditions, spectrum savings up to 42% can be obtained if elastic spectrum allocation is considered compared to rigid spectrum allocation. Furthermore, according to the results the current spectral resources of CEDIA network will be exhausted by mid-2023 using spectrum allocation based on Mixed-Line-Rate (MLR) WDM, while this estimation will extend until near 2025 if allocation based on Flex-Grid is considered.

This paper overviews the approach of the Elastic Networks research network to address different issues of planning and control of Flex-Grid/SDM optical networks. Firstly, we present the Net2Plan open-source planning tool capabilities to model Flex-Grid/SDM networks; secondly a PCE-based Transport-SDN controller for packet over flex-grid optical networks is described. Finally results on machine-learning-based QoT classification techniques useful in planning and control tasks are reported.

We propose and evaluate a dynamic traffic grooming strategy enhancing the performance of JoS-enabled Flex-Grid/SDM networks. Results disclose up to 120% and 44% additional carried network traffic vs. no grooming and existing end-to-end traffic grooming solutions, respectively.

To effectively keep pace with the global IP traffic growth forecasted in the years to come, flex-grid over multi-core fiber (MCF) networks can bring superior spectrum utilization flexibility, as well as bandwidth scalability far beyond the non-linear Shannon’s limit. In such a network scenario, however, full node switching re-configurability will require enormous node complexity, pushing the limits of current optical device technologies with prohibitive capital expenditures. Therefore, cost-effective node solutions will most probably be the key enablers of flex-grid/MCF networks, at least in the short- and mid-term future. In this context, this paper proposes a cost-effective reconfigurable optical add/drop multiplexer (ROADM) architecture for flex-grid/MCF networks, called CCC-ROADM, which reduces technological requirements (and associated costs) in exchange for demanding core continuity along the end-to-end communication. To assess the performance of the proposed CCC-ROADM in comparison with a fully flexible ROADM (i.e., a fully non-blocking ROADM, called FNB-ROADM in this work) in large-scale network scenarios, a novel lightweight heuristic to solve the route, modulation, core, and spectrum assignment problem in flex-grid/MCF networks is presented in this work, whose goodness is successfully validated against optimal ILP formulations previously proposed for the same goal. The obtained numerical results in a significant number of representative network topologies with different MCF configurations of 7, 12, and 19 cores show almost identical network performance in terms of maximum network throughput when deploying CCC-ROADMs versus FNB-ROADMs, while decreasing network capital expenditures to a large extent.

Space Division Multiplexing (SDM) is a key technology to cope with the bandwidth limitations of single mode fibers. Multi-Core Fibers (MCFs) are considered as a promising candidate technology to implement SDM, due to their low inter-core crosstalk (ICXT), experimentally proven in laboratory prototypes. Among the different channel allocation options making use of the newly enabled space dimension, the so-called spatial super-channel (Spa-SCh) is the most likely solution to be implemented, given the inherent cost reduction of the joint-switching operation (i.e., jointly switching a spectrum portion in all MCF cores at once). This work targets the cost-effective Spa-SCh allocation over MCF-enabled Flex-Grid optical core networks. To this goal, state-of-the-art 22-core MCFs are assumed, although the proposed solutions are applicable to any MCF type. In particular, we propose and evaluate a partial-core assignment as a cost-effective strategy to improve spectrum utilization and save Capital Expenditure (CapEx) costs by minimizing the number of optical transceivers used per Spa-SCh. Numerical results reveal that reductions up to 44% and 33% in the number of active transceivers in the network can be obtained in national- and continental-wide backbone networks, respectively, without affecting the network Grade-of-Service (GoS), measured in terms of Bandwidth Blocking Probability (BBP). To evaluate the impact of the ICXT, we also compare the performance of the MCF scenarios under study against equivalent Multi-Fiber (MF) ones. From the obtained results, ICXT in MCF scenarios requires the utilization of less efficient modulation formats, which reduces the admissible offered network load by up to 17% for a 1% BBP target. Furthermore, this lower spectral efficiency also demands an increase of the symbol rate per sub-channel up to a 26%, a key indicator of the modulator electronic complexity.

Spatial Division Multiplexing (SDM) arises as the only solution to overcome the capacity limits of single-mode optical fibres (SMFs). Among the different SDM flavours, Multi-Core Fibres (MCFs) are gaining interest thanks to their low inter-core crosstalk (XT). In this context, Flex-Grid is envisioned as the technology that enables the efficient allocation of connections in SDM-based optical networks. Despite the benefits that the combination of Flex-Grid/SDM brings, the necessary guard-bands between connections can limit the performance, especially when allocating spatial super channels. In this paper, we evaluate the influence of the guard-band width on the performance of dynamic Flex-Grid/SDM optical networks when allocating spatial super-channel connections. The obtained results reveal that significant improvements can be achieved for reduced guard-band requirements.

Universitat Politecnica de Catalunya (UPC), C/Jordi Girona 1–3, 08034 Barcelona, Spain We quantify the network capacity scaling from 7 to 30 spatial channels. While multi-fiber provides a 5× capacity increase, MCF limits it to 4× and 2× in national and continental backbone networks, respectively.

The majority of the research studies on Flex-Grid over multi-core fiber (Flex-Grid/MCF) networks are built on the assumption of fully non-blocking ROADMs (FNB-ROADMs), able to switch any portion of the spectrum from any input core of any input fiber to any output core of any output fiber. Such flexibility comes at an enormous extra hardware cost. In this paper, we explore the trade-off of using ROADMs that impose the so-called core continuity constraint (CCC). Namely, a CCC-ROADM can switch spectrum from a core on an input fiber to a chosen output fiber, but cannot choose the specific output core. For instance, if all fibers have the same number of cores, the i-th core in the input fibers can be just switched to the i-th core in the output fibers. To evaluate the performance vs. cost trade-off of using CCCROADMs, we present two Integer Linear Programming (ILP) formulations for optimally allocating incoming demands in Flex-Grid/MCF networks, where the CCC constraint is imposed or not, respectively. A set of results are extracted applying both schemes in two different backbone networks. Transmission reach estimations are conducted accounting for the fiber’s linear and non-linear effects, as well as the inter-core crosstalk (ICXT) impairment introduced by laboratory MCF prototypes of 7, 12 and 19 cores. Our numerical evaluations show that the performance penalty of CCC is minimal, i.e., below 1% for 7 and 12-core MCF and up to 10% for 19-core MCF, while the cost reduction is large. In addition, results reveal that the ICXT effect can be significant when the number of cores per MCF is high, up to a point that equipping the network with 12-core MCFs can yield superior effective capacity than with 19-core MCFs.

© 2019 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved. We study inter-core crosstalk (ICXT) impact on migration planning toward spectrally-spatially flexible optical networks considering 22-core multi-core fiber. Results reveal that 55-70% of links need to be upgraded when ICXT ranges from -68.2 to -43.4 dB/km.

We focus on a migration planning from elastic to spectrally-spatially flexible optical networks by upgrading regular with SDM-capable ROADMs. Our most promising strategy reveals that by migrating 30% of the regular ROADMs a 2x carried traffic increase can be achieved.