36 research outputs found
Physical Layer Aware Optical Networks
This thesis describes novel contributions in the field of physical layer aware optical networks. IP traffic increase and revenue compression in the Telecom
industry is putting a lot of pressure on the optical community to develop novel solutions that must both increase total capacity while being cost effective. This requirement is pushing operators towards network disaggregation, where optical network infrastructure is built by mix and match different physical layer technologies from different vendors. In such a novel context, every equipment and transmission technique at the physical layer impacts the overall network behavior. Hence, methods giving quantitative evaluations of individual merit of physical layer equipment at network level are a
firm request during network design phases as well as during network lifetime. Therefore, physical layer awareness in network design and operation is fundamental to fairly assess the potentialities, and exploit the capabilities of different technologies. From this perspective, propagation impairments modeling is essential. In this work propagation impairments in transparent optical networks are summarized, with a special focus on nonlinear effects. The Gaussian Noise model is reviewed, then extended for wideband scenarios. To do so, the impact of polarization mode dispersion on nonlinear interference (NLI) generation is assessed for the first time through simulation, showing its negligible impact on NLI generation. Thanks to this result, the Gaussian Noise model is generalized to assess the impact of space and frequency amplitude variations along the fiber, mainly due to stimulated Raman scattering, on NLI generation. The proposed Generalized GN (GGN) model is experimentally validated on
a setup with commercial linecards, compared with other modeling options, and an example of application is shown. Then, network-level power optimization strategies are discussed, and
the Locally Optimization Global Optimization (LOGO) approach reviewed. After that, a novel framework of analysis for optical networks that leverages detailed propagation impairment modeling called the Statistical Network Assessment Process (SNAP) is presented. SNAP is motivated by the need of having a general framework to assess the impact of different physical layer technologies on network performance, without relying on rigid optimization approaches, that are not well-suited for technology comparison. Several examples of applications of SNAP are given, including comparisons of transceivers, amplifiers and node technologies. SNAP is also used to highlight topological bottlenecks in progressively loaded network scenarios and to derive possible solutions for them.
The final work presented in this thesis is related to the implementation of a vendor agnostic quality of transmission estimator for multi-vendor optical networks developed in the context of the Physical Simulation Environment group of the Telecom Infra Project. The implementation of a module based on the GN model is briefly described, then results of a multi-vendor experimental validation performed in collaboration with Microsoft are shown
Design, monitoring and performance evaluation of high capacity optical networks
Premi Extraordinari de Doctorat, promoció 2018-2019. Àmbit de les TICInternet traffic is expected to keep increasing exponentially due to the emergence of a vast number of innovative online services and applications. Optical networks, which are the cornerstone of the underlying Internet infrastructure, have been continuously evolving to carry the ever-increasing traffic in a more flexible, cost-effective, and intelligent way. Having these three targets in mind, this PhD thesis focuses on two general areas for the performance improvement and the evolution of optical networks: i) introducing further cognition to the optical layer, and ii) introducing new networking solutions revolutionizing the optical transport infrastructure. In the first part, we present novel failure detection and identification solutions in the optical layer utilizing the optical spectrum traces captured by cost-effective coarse-granular Optical Spectrum Analyzers (OSA). We demonstrate the effectiveness of the developed solutions for detecting and identifying filter-related failures in the context of Spectrum-Switched Optical Networks (SSON), as well as transmitter-related laser failures in Filter-less Optical Networks (FON). In addition, at the subsystem level we propose an Autonomic Transmission Agent (ATA), which triggers local or remote transceiver reconfiguration by predicting Bit-Error-Rate (BER) degradation by monitoring State-of-Polarization (SOP) data obtained by coherent receivers. I have developed solutions to push further the performance of the currently deployed optical networks through reducing the margins and introducing intelligence to better manage their resources. However, it is expected that the spectral efficiency of the current standard Single-Mode Fiber (SMF) based optical network approaches the Shannon capacity limits in the near future, and therefore, a new paradigm is required to keep with the pace of the current huge traffic increase. In this regard, Space Division Multiplexing (SDM) is proposed as the ultimate solution to address the looming capacity crunch with a reduced cost-per-bit delivered to the end-users. I devote the second part of this thesis to investigate different flavors of SDM based optical networks with the aim of finding the best compromise for the realization of a spectrally and spatially flexible optical network. SDM-based optical networks can be deployed over various types of transmission media. Additionally, due to the extra dimension (i.e., space) introduced in SDM networks, optical switching nodes can support wavelength granularity, space granularity, or a combination of both. In this thesis, we evaluate the impact of various spectral and spatial switching granularities on the performance of SDM-based optical networks serving different profiles of traffic with the aim of understanding the impact of switching constraints on the overall network performance. In this regard, we consider two different generations of wavelength selective switches (WSS) to reflect the technology limitations on the performance of SDM networks. In addition, we present different designs of colorless direction-less, and Colorless Directionless Contention-less (CDC) Reconfigurable Optical Add/Drop Multiplexers (ROADM) realizing SDM switching schemes and compare their performance in terms of complexity and implementation cost. Furthermore, with the aim of revealing the benefits and drawbacks of SDM networks over different types of transmission media, we preset a QoT-aware network planning toolbox and perform comparative performance analysis among SDM network based on various types of transmission media. We also analyze the power consumption of Multiple-Input Multiple-Output (MIMO) Digital Signal Processing (DSP) units of transceivers operating over three different types of transmission media. The results obtained in the second part of the thesis provide a comprehensive outlook to different realizations of SDM-based optical networks and showcases the benefits and drawbacks of different SDM realizations.Se espera que el tráfico de Internet siga aumentando exponencialmente debido a la continua aparición de gran cantidad de aplicaciones innovadoras. Las redes ópticas, que son la piedra angular de la infraestructura de Internet, han evolucionado continuamente para transportar el tráfico cada vez mayor de una manera más flexible, rentable e inteligente. Teniendo en cuenta estos tres objetivos, esta tesis doctoral se centra en dos áreas cruciales para la mejora del rendimiento y la evolución de las redes ópticas: i) introducción de funcionalidades cognitivas en la capa óptica, y ii) introducción de nuevas estructuras de red que revolucionarán el transporte óptico. En la primera parte, se presentan soluciones novedosas de detección e identificación de fallos en la capa óptica que utilizan trazas de espectro óptico obtenidas mediante analizadores de espectros ópticos (OSA) de baja resolución (y por tanto de coste reducido). Se demuestra la efectividad de las soluciones desarrolladas para detectar e identificar fallos derivados del filtrado imperfecto en las redes ópticas de conmutación de espectro (SSON), asà como fallos relacionados con el láser transmisor en redes ópticas sin filtro (FON). Además, a nivel de subsistema, se propone un Agente de Transmisión Autónomo (ATA), que activa la reconfiguración del transceptor local o remoto al predecir la degradación de la Tasa de Error por Bits (BER), monitorizando el Estado de Polarización (SOP) de la señal recibida en un receptor coherente. Se han desarrollado soluciones para incrementar el rendimiento de las redes ópticas mediante la reducción de los márgenes y la introducción de inteligencia en la administración de los recursos de la red. Sin embargo, se espera que la eficiencia espectral de las redes ópticas basadas en fibras monomodo (SMF) se acerque al lÃmite de capacidad de Shannon en un futuro próximo, y por tanto, se requiere un nuevo paradigma que permita mantener el crecimiento necesario para soportar el futuro aumento del tráfico. En este sentido, se propone el Multiplexado por División Espacial (SDM) como la solución que permita la continua reducción del coste por bit transmitido ante ése esperado crecimiento del tráfico. En la segunda parte de esta tesis se investigan diferentes tipos de redes ópticas basadas en SDM con el objetivo de encontrar soluciones para la realización de redes ópticas espectral y espacialmente flexibles. Las redes ópticas basadas en SDM se pueden implementar utilizando diversos tipos de medios de transmisión. Además, debido a la dimensión adicional (el espacio) introducida en las redes SDM, los nodos de conmutación óptica pueden conmutar longitudes de onda, fibras o una combinación de ambas. Se evalúa el impacto de la conmutación espectral y espacial en el rendimiento de las redes SDM bajo diferentes perfiles de tráfico ofrecido, con el objetivo de comprender el impacto de las restricciones de conmutación en el rendimiento de la red. En este sentido, se consideran dos generaciones diferentes de conmutadores selectivos de longitud de onda (WSS) para reflejar las limitaciones de la tecnologÃa en el rendimiento de las redes SDM. Además, se presentan diferentes diseños de ROADM, independientes de la longitud de onda, de la dirección, y sin contención (CDC) utilizados para la conmutación SDM, y se compara su rendimiento en términos de complejidad y coste. Además, con el objetivo de cuantificar los beneficios e inconvenientes de las redes SDM, se ha generado una herramienta de planificación de red que prevé la QoT usando diferentes tipos de fibras. También se analiza el consumo de energÃa de las unidades DSP de los transceptores MIMO operando en redes SDM con tres tipos diferentes de medios de transmisión. Los resultados obtenidos en esta segunda parte de la tesis proporcionan una perspectiva integral de las redes SDM y muestran los beneficios e inconvenientes de sus diferentes implementacionesAward-winningPostprint (published version
Physical layer aware open optical networking
L'abstract è presente nell'allegato / the abstract is in the attachmen
Domain/Multi-Domain Protection and Provisioning in Optical Networks
L’évolution récente des commutateurs de sélection de longueurs d’onde (WSS -Wavelength Selective Switch) favorise le développement du multiplexeur optique d’insertionextraction reconfigurable (ROADM - Reconfigurable Optical Add/Drop Multiplexers) à plusieurs degrés sans orientation ni coloration, considéré comme un équipement fort prometteur pour les réseaux maillés du futur relativement au multiplexage en longueur d’onde (WDM -Wavelength Division Multiplexing ). Cependant, leur propriété de commutation asymétrique complique la question de l’acheminement et de l’attribution des longueur d’ondes (RWA - Routing andWavelength Assignment). Or la plupart des algorithmes de RWA existants ne tiennent pas compte de cette propriété d’asymétrie.
L’interruption des services causée par des défauts d’équipements sur les chemins
optiques (résultat provenant de la résolution du problème RWA) a pour conséquence la
perte d’une grande quantité de données. Les recherches deviennent ainsi incontournables afin d’assurer la survie fonctionnelle des réseaux optiques, à savoir, le maintien des services, en particulier en cas de pannes d’équipement. La plupart des publications antérieures portaient particulièrement sur l’utilisation d’un système de protection permettant de garantir le reroutage du trafic en cas d’un défaut d’un lien. Cependant, la conception de la protection contre le défaut d’un lien ne s’avère pas toujours suffisante en termes de survie des réseaux WDM à partir de nombreux cas des autres types de pannes devenant courant de nos jours, tels que les bris d’équipements, les pannes de deux ou trois liens, etc. En outre, il y a des défis considérables pour protéger les grands réseaux optiques multidomaines composés de réseaux associés à un domaine simple, interconnectés par des liens interdomaines, où les détails topologiques internes d’un domaine ne sont généralement pas partagés à l’extérieur.
La présente thèse a pour objectif de proposer des modèles d’optimisation de grande
taille et des solutions aux problèmes mentionnés ci-dessus. Ces modèles-ci permettent de générer des solutions optimales ou quasi-optimales avec des écarts d’optimalité mathématiquement prouvée. Pour ce faire, nous avons recours à la technique de génération de colonnes afin de résoudre les problèmes inhérents à la programmation linéaire de
grande envergure.
Concernant la question de l’approvisionnement dans les réseaux optiques, nous proposons
un nouveau modèle de programmation linéaire en nombres entiers (ILP - Integer
Linear Programming) au problème RWA afin de maximiser le nombre de requêtes acceptées
(GoS - Grade of Service). Le modèle résultant constitue celui de l’optimisation
d’un ILP de grande taille, ce qui permet d’obtenir la solution exacte des instances RWA
assez grandes, en supposant que tous les noeuds soient asymétriques et accompagnés
d’une matrice de connectivité de commutation donnée. Ensuite, nous modifions le modèle
et proposons une solution au problème RWA afin de trouver la meilleure matrice de
commutation pour un nombre donné de ports et de connexions de commutation, tout en
satisfaisant/maximisant la qualité d’écoulement du trafic GoS.
Relativement à la protection des réseaux d’un domaine simple, nous proposons des
solutions favorisant la protection contre les pannes multiples. En effet, nous développons
la protection d’un réseau d’un domaine simple contre des pannes multiples, en utilisant
les p-cycles de protection avec un chemin indépendant des pannes (FIPP - Failure Independent
Path Protecting) et de la protection avec un chemin dépendant des pannes
(FDPP - Failure Dependent Path-Protecting). Nous proposons ensuite une nouvelle formulation
en termes de modèles de flots pour les p-cycles FDPP soumis à des pannes
multiples. Le nouveau modèle soulève un problème de taille, qui a un nombre exponentiel
de contraintes en raison de certaines contraintes d’élimination de sous-tour. Par
conséquent, afin de résoudre efficacement ce problème, on examine : (i) une décomposition
hiérarchique du problème auxiliaire dans le modèle de décomposition, (ii) des
heuristiques pour gérer efficacement le grand nombre de contraintes.
À propos de la protection dans les réseaux multidomaines, nous proposons des systèmes
de protection contre les pannes d’un lien. Tout d’abord, un modèle d’optimisation
est proposé pour un système de protection centralisée, en supposant que la gestion du
réseau soit au courant de tous les détails des topologies physiques des domaines. Nous
proposons ensuite un modèle distribué de l’optimisation de la protection dans les réseaux
optiques multidomaines, une formulation beaucoup plus réaliste car elle est basée
sur l’hypothèse d’une gestion de réseau distribué. Ensuite, nous ajoutons une bande pasiv
sante partagée afin de réduire le coût de la protection. Plus précisément, la bande passante
de chaque lien intra-domaine est partagée entre les p-cycles FIPP et les p-cycles
dans une première étude, puis entre les chemins pour lien/chemin de protection dans une
deuxième étude. Enfin, nous recommandons des stratégies parallèles aux solutions de
grands réseaux optiques multidomaines.
Les résultats de l’étude permettent d’élaborer une conception efficace d’un système
de protection pour un très large réseau multidomaine (45 domaines), le plus large examiné
dans la littérature, avec un système à la fois centralisé et distribué.Recent developments in the wavelength selective switch (WSS) technology enable
multi-degree reconfigurable optical add/drop multiplexers (ROADM) architectures with
colorless and directionless switching, which is regarded as a very promising enabler for
future reconfigurable wavelength division multiplexing (WDM) mesh networks. However,
its asymmetric switching property complicates the optimal routing and wavelength
assignment (RWA) problem, which is NP-hard. Most of the existing RWA algorithms
do not consider such property.
Disruption of services through equipment failures on the lightpaths (output of RWA
problem) is consequential as it involves the lost of large amounts of data. Therefore,
substantial research efforts are needed to ensure the functional survivability of optical
networks, i.e., the continuation of services even when equipment failures occur. Most
previous publications have focused on using a protection scheme to guarantee the traffic
connections in the event of single link failures. However, protection design against single
link failures turns out not to be always sufficient to keep the WDM networks away from
many downtime cases as other kinds of failures, such as node failures, dual link failures,
triple link failures, etc., become common nowadays. Furthermore, there are challenges
to protect large multi-domain optical networks which are composed of several singledomain
networks, interconnected by inter-domain links, where the internal topological
details of a domain are usually not shared externally.
The objective of this thesis is to propose scalable models and solution methods for
the above problems. The models enable to approach large problem instances while producing
optimal or near optimal solutions with mathematically proven optimality gaps.
For this, we rely on the column generation technique which is suitable to solve large
scale linear programming problems.
For the provisioning problem in optical networks, we propose a new ILP (Integer
Linear Programming) model for RWA problem with the objective of maximizing the
Grade of Service (GoS). The resulting model is a large scale optimization ILP model,
which allows the exact solution of quite large RWA instances, assuming all nodes are
asymmetric and with a given switching connectivity matrix. Next, we modify the model
and propose a solution for the RWA problem with the objective of finding the best switching
connectivity matrix for a given number of ports and a given number of switching
connections, while satisfying/maximizing the GoS.
For protection in single domain networks, we propose solutions for the protection
against multiple failures. Indeed, we extent the protection of a single domain network
against multiple failures, using FIPP and FDPP p-cycles. We propose a new generic
flow formulation for FDPP p-cycles subject to multiple failures. Our new model ends
up with a complex pricing problem, which has an exponential number of constraints due
to some subtour elimination constraints. Consequently, in order to efficiently solve the
pricing problem, we consider: (i) a hierarchical decomposition of the original pricing
problem; (ii) heuristics in order to go around the large number of constraints in the
pricing problem.
For protection in multi-domain networks, we propose protection schemes against
single link failures. Firstly, we propose an optimization model for a centralized protection
scheme, assuming that the network management is aware of all the details of the
physical topologies of the domains. We then propose a distributed optimization model
for protection in multi-domain optical networks, a much more realistic formulation as it
is based on the assumption of a distributed network management. Then, we add bandwidth
sharing in order to reduce the cost of protection. Bandwidth of each intra-domain
link is shared among FIPP p-cycles and p-cycles in a first study, and then among paths
for link/path protection in a second study. Finally, we propose parallel strategies in order
to obtain solutions for very large multi-domain optical networks.
The result of this last study allows the efficent design of a protection scheme for a
very large multi-domain network (45 domains), the largest one by far considered in the
literature, both with a centralized and distributed scheme