Exhaustive Search for Optimal Offline Spectrum Assignment in Elastic Optical Networks

Heuristic-based approaches are widely deployed in solving Spectrum Assignment problem. This causes the results to be unreliable in some test cases when the results are very far from the lowerbound. This paper presents an exhaustive search approach that starts with an initial seed of a solution achieved by a heuristic-based algorithm called “Longest First Fit” (LFF) and tries all possible permutations starting from this initial seed. The algorithm skips some branches and all its descendant permutations if it meets certain criteria that guarantees that those permutations will not lead to a better result. The experimental results show that the new algorithm has succeeded in achieving the lower-bound in 93% of the randomly generated test cases while the heuristic solver LFF can achieve 65%. The algorithm achieves these results in a reasonable running time of less than 10 seconds

Combination of Advanced Reservation and Resource Periodic Arrangement for RMSA in EON with Deep Reinforcement Learning

The Elastic Optical Networks (EON) provide a solution to the massive demand for connections and extremely high data traffic with the Routing Modulation and Spectrum Assignment (RMSA) as a challenge. In previous RMSA research, there was a high blocking probability because the route to be passed by the K-SP method with a deep neural network approach used the First Fit policy, and the modulation problem was solved with Modulation Format Identification (MFI) or BPSK using Deep Reinforcement Learning. The issue might be apparent in spectrum assignment because of the influence of Advanced Reservation (AR) and Resource Periodic Arrangement (RPA), which is a decision block on a connection request path with both idle and active data traffic. The study’s limitation begins with determining the modulation of m = 1 and m = 4, followed by the placement of frequencies, namely 13 with a combination of standard block frequencies 41224–24412, so that the simulation results are less than 0.0199, due to the combination of block frequency slices with spectrum allocation rule techniques.

A constrained maximum available frequency slots on path based online routing and spectrum allocation for dynamic traffic in elastic optical networks

Elastic optical networking is a potential candidate to support dynamic traffic with heterogeneous data rates and variable bandwidth requirements with the support of the optical orthogonal frequency division multiplexing technology (OOFDM). During the dynamic network operation, lightpath arrives and departs frequently and the network status updates accordingly. Fixed routing and alternate routing algorithms do not tune according to the current network status which are computed offline. Therefore, offline algorithms greedily use resources with an objective to compute shortest possible paths and results in high blocking probability during dynamic network operation. In this paper, adaptive routing algorithms are proposed for shortest path routing as well as alternate path routing which make routing decision based on the maximum idle frequency slots (FS) available on different paths. The proposed algorithms select an underutilized path between different choices with maximum idle FS and efficiently avoids utilizing a congested path. The proposed routing algorithms are compared with offline routing algorithms as well as an existing adaptive routing algorithm in different network scenarios. It has been shown that the proposed algorithms efficiently improve network performance in terms of FS utilization and blocking probability during dynamic network operation

Transferências de dados em massa sensíveis ao consumo energético em Redes Ópticas Elásticas

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Exatas, Departamento de Ciência da Computação, 2019.O tráfego entre Data Centers (Centro de dados – CD) na Internet tem crescido de maneira relevante nas duas últimas décadas e a tendência é que essa demanda aumente ainda mais principalmente nas redes de núcleo em função de serviços que geram grande volume de tráfego tais como aplicações de vídeo, computação em nuvem, dentre outros. Para tal, estudos têm sido feitos para que haja um maior aproveitamento da largura de banda nas redes ópticas. Muitos destes estudos estão pautados no advento das Redes Ópticas Elásticas (Elastic Optical Networks – EONs); as quais possibilitam um maior aproveitamento espectral do meio de transmissão óptico. Diversas características das EONs precisam ser aperfeiçoadas, dentre elas a eficiência energética, haja vista que o consumo sustentável é necessário. Em meio a estas temáticas há, também, as Transferências de Dados em Massa (Bulk Data Transfers – BDT), operação frequente entre CDs com grandes volumes de dados, tolerantes a atraso e com alto consumo de energia. Há, então, uma necessidade de estudar e propor soluções para transações de grande fluxo de dados entre CDs cientes de eficiência energética considerando o paradigma das Redes Ópticas Elásticas. Portanto, este trabalho visa propor soluções para o transporte de BDTs entre CDs com eficiência energética em uma EON.The inter Data Centers (IDC) traffic on the Internet has grown considerably over the last two decades, and the trend is that this demand will increase even more especially in core networks because of services that generate large volumes of traffic such as video applications, cloud computing, among others. To this new class of applications, studies have been done to better explore the available bandwidth in optical networks. Many of these studies are considering the advent of Elastic Optical Networks (EONs); which make possible a better spectral utilization of the optical transmission medium. Several characteristics of EONs need to be improved, including energy efficiency; given that sustainable consumption is necessary. Moreover there are Bulk Data Transfers (BDT), which are frequent IDC operations with large volumes of data, delay tolerance and with high energy consumption. There is, therefore, a need to study and propose feasible solutions for enabling energy-aware large data flow IDC transactions on top of an Elastic Optical Network infrastructure. Therefore, this work aims to propose solutions for the transport of IDC BDTs with energy-efficient in an EON

In-operation planning in flexgrid optical core networks

New generation applications, such as cloud computing or video distribution, can run in a telecom cloud infrastructure where the datacenters (DCs) of telecom operators are integrated in their networks thus, increasing connections' dynamicity and resulting in time-varying traffic capacities, which might also entail changes in the traffic direction along the day. As a result, a flexible optical technology able to dynamically set-up variable-capacity connections, such as flexgrid, is needed. Nonetheless, network dynamicity might entail network performance degradation thus, requiring re-optimizing the network while it is in operation. This thesis is devoted to devise new algorithms to solve in-operation network planning problems aiming at enhancing the performance of optical networks and at studying their feasibility in experimental environments. In-operation network planning requires from an architecture enabling the deployment of algorithms that must be solved in stringent times. That architecture can be based on a Path Computation Element (PCE) or a Software Defined Networks controller. In this thesis, we assume the former split in a front-end PCE, in charge of provisioning paths and handling network events, and a specialized planning tool in the form of a back-end PCE responsible for solving in-operation planning problems. After the architecture to support in-operation planning is assessed, we focus on studying the following applications: 1) Spectrum fragmentation is one of the most important problems in optical networks. To alleviate it to some extent without traffic disruption, we propose a hitless spectrum defragmentation strategy. 2) Each connection affected by a failure can be recovered using multiple paths to increase traffic restorability at the cost of poor resource utilization. We propose re-optimizing the network after repairing the failure to aggregate and reroute those connections to release spectral resources. 3) We study two approaches to provide multicast services: establishing a point-to-multipoint connections at the optical layer and using multi-purpose virtual network topologies (VNT) to serve both unicast and multicast connectivity requests. 4) The telecom cloud infrastructure, enables placing contents closer to the users. Based on it, we propose a hierarchical content distribution architecture where VNTs permanently interconnect core DCs and metro DCs periodically synchronize contents to the core DCs. 5) When the capacity of the optical backbone network becomes exhausted, we propose using a planning tool with access to inventory and operation databases to periodically decide the equipment and connectivity to be installed at the minimum cost reducing capacity overprovisioning. 6) In multi-domain multi-operator scenarios, a broker on top of the optical domains can provision multi-domain connections. We propose performing intra-domain spectrum defragmentation when no contiguous spectrum can be found for a new connection request. 7) Packet nodes belonging to a VNT can collect and send incoming traffic monitoring data to a big data repository. We propose using the collected data to predict next period traffic and to adapt the VNT to future conditions. The methodology followed in this thesis consists in proposing a problem statement and/or a mathematical formulation for the problems identified and then, devising algorithms for solving them. Those algorithms are simulated and then, they are experimentally assessed in real test-beds. This thesis demonstrates the feasibility of performing in-operation planning in optical networks, shows that it enhances the performance of the network and validates the feasibility of its deployment in real networks. It shall be mentioned that part of the work reported in this thesis has been done within the framework of several research projects, namely IDEALIST (FP7-ICT-2011-8) and GEANT (238875) funded by the EC and SYNERGY (TEC2014-59995-R) funded by the MINECO.Les aplicacions de nova generació, com ara el cloud computing o la distribució de vídeo, es poden executar a infraestructures de telecom cloud (TCI) on operadors integren els seus datacenters (DC) a les seves xarxes. Aquestes aplicacions fan que incrementi tant la dinamicitat de les connexions, com la variabilitat de les seves capacitats en el temps, arribant a canviar de direcció al llarg del dia. Llavors, cal disposar de tecnologies òptiques flexibles, tals com flexgrid, que suportin aquesta dinamicitat a les connexions. Aquesta dinamicitat pot degradar el rendiment de la xarxa, obligant a re-optimitzar-la mentre és en operació. Aquesta tesis està dedicada a idear nous algorismes per a resoldre problemes de planificació sobre xarxes en operació (in-operation network planning) per millorar el rendiment de les xarxes òptiques i a estudiar la seva factibilitat en entorns experimentals. Aquests problemes requereixen d’una arquitectura que permeti desplegar algorismes que donin solucions en temps restrictius. L’arquitectura pot estar basada en un Element de Computació de Rutes (PCE) o en un controlador de Xarxes Definides per Software. En aquesta tesis, assumim un PCE principal encarregat d’aprovisionar rutes i gestionar esdeveniments de la xarxa, i una eina de planificació especialitzada en forma de PCE de suport per resoldre problemes d’in-operation planning. Un cop validada l’arquitectura que dona suport a in-operation planning, estudiarem les següents aplicacions: 1) La fragmentació d’espectre és un dels principals problemes a les xarxes òptiques. Proposem reduir-la en certa mesura, fent servir una estratègia que no afecta al tràfic durant la desfragmentació. 2) Cada connexió afectada per una fallada pot ser recuperada fent servir múltiples rutes incrementant la restaurabilitat de la xarxa, tot i empitjorar-ne la utilització de recursos. Proposem re-optimitzar la xarxa després de reparar una fallada per agregar i re-enrutar aquestes connexions tractant d’alliberar recursos espectrals. 3) Estudiem dues solucions per aprovisionar serveis multicast: establir connexions punt-a-multipunt sobre la xarxa òptica i utilitzar Virtual Network Topologies (VNT) multi-propòsit per a servir peticions de connectivitat tant unicast com multicast. 4) La TCI permet mantenir els continguts a prop dels usuaris. Proposem una arquitectura jeràrquica de distribució de continguts basada en la TCI, on els DC principals s’interconnecten per mitjà de VNTs permanents i els DCs metropolitans periòdicament sincronitzen continguts amb els principals. 5) Quan la capacitat de la xarxa òptica s’exhaureix, proposem utilitzar una eina de planificació amb accés a bases de dades d’inventari i operacionals per decidir periòdicament l’equipament i connectivitats a instal·lar al mínim cost i reduir el sobre-aprovisionament de capacitat. 6) En entorns multi-domini multi-operador, un broker per sobre dels dominis òptics pot aprovisionar connexions multi-domini. Proposem aplicar desfragmentació d’espectre intra-domini quan no es pot trobar espectre contigu per a noves peticions de connexió. 7) Els nodes d’una VNT poden recollir i enviar informació de monitorització de tràfic entrant a un repositori de big data. Proposem utilitzar aquesta informació per adaptar la VNT per a futures condicions. La metodologia que hem seguit en aquesta tesis consisteix en formalitzar matemàticament els problemes un cop aquests son identificats i, després, idear algorismes per a resoldre’ls. Aquests algorismes son simulats i finalment validats experimentalment en entorns reals. Aquesta tesis demostra la factibilitat d’implementar mecanismes d’in-operation planning en xarxes òptiques, mostra els beneficis que aquests aporten i valida la seva aplicabilitat en xarxes reals. Part del treball presentat en aquesta tesis ha estat dut a terme en el marc dels projectes de recerca IDEALIST (FP7-ICT-2011-8) i GEANT (238875), finançats per la CE, i SYNERGY (TEC2014-59995-R), finançat per el MINECO.Postprint (published version

Enabling Technology in Optical Fiber Communications: From Device, System to Networking

This book explores the enabling technology in optical fiber communications. It focuses on the state-of-the-art advances from fundamental theories, devices, and subsystems to networking applications as well as future perspectives of optical fiber communications. The topics cover include integrated photonics, fiber optics, fiber and free-space optical communications, and optical networking

Optical network planning for static applications

Traffic demands on optical transport networks continue to grow, both in numbers and in size, at an incredible rate. Consequently, the efficient use of network resources has never been as important as today. A possible solution to this problem is to plan, develop and implement efficient algorithms for static and/or dynamic applications in order to minimize the probability of blocking and/or minimizing the number of wavelengths. Static Routing and Wavelength Assignment (RWA) algorithms use a given set of optical path requests and are intended to provide a long-term plan for future traffic. Static RWA algorithms are important for current and future WDM (Wavelength-Division Multiplexing) networks, especially when there is no wavelength conversion, the network is highly connected or the traffic load is moderate to high. In this dissertation, we propose to develop an optical network planning tool capable of choosing the best optical path and assigning as few wavelengths as possible. This tool is structured in five phases: in the first phase, the network physical topology is defined by the adjacency matrix or by the cost matrix and the logical topology is defined by the traffic matrix; in a second phase, the Dijkstra algorithm is used to find the shortest path for each connection; in the third phase, the traffic routing is accomplished considering one traffic unit between the source and destination nodes; in the fourth phase, the paths are ordered using various ordering strategies, such as Shortest Path First, Longest Path First and Random Path Order; finally, in the fifth phase, the heuristic algorithms for wavelength assignment, such as Graph Coloring, First-Fit and Most-Used are used. This tool is first tested on small networks (e.g. ring and mesh topologies), and then applied to real networks (e.g. COST 239, NSFNET and UBN topologies). We have concluded that the number of wavelengths calculated for each network is almost independent of the Wavelength Assignment (WA) heuristics, as well as the ordering strategy, when a full mesh logical topology is considered.Os pedidos de tráfego nas redes de transporte ópticas continuam a crescer, tanto em número como em tamanho, a um ritmo incrível. Consequentemente, a utilização eficiente dos recursos das redes nunca foi tão importante como hoje. Uma solução possível para este problema passa por planear, desenvolver e implementar algoritmos eficientes para aplicações estáticas e/ou dinâmicas de modo a minimizar a probabilidade de bloqueio e/ou minimizar o número de comprimentos de onda. Os algoritmos de encaminhamento e de atribuição de comprimentos de onda (RWA) estáticos utilizam um determinado conjunto de pedidos de caminhos ópticos e visam fornecer um plano de longo prazo para tráfego futuro. Os algoritmos RWA estáticos são importantes para as redes em multiplexagem por divisão de comprimento de onda (WDM) atuais e futuras, especialmente quando não há conversão de comprimento de onda, a rede é altamente ligada ou a carga de tráfego é de moderada a alta. Nesta dissertação, propomos desenvolver uma ferramenta de planeamento de redes ópticas capaz de escolher o melhor caminho óptico e atribuir o mínimo de comprimentos ondas possíveis. Esta ferramenta está estruturada em cinco fases: numa primeira fase é definida a topologia física de rede pela matriz das adjacências ou pela matriz de custo e a topologia lógica é definida pela matriz de tráfego; numa segunda fase é utilizado o algoritmo Dijkstra para encontrar o caminho mais curto para cada ligação; na terceira fase o encaminhamento de tráfego é realizado considerando uma unidade de tráfego entre os nós de origem e destino; na quarta fase os caminhos são ordenados tendo em conta as várias estratégias de ordenação, tais como Shortest Path First, Longest Path First e Random Path Order; finalmente, na quinta fase, os algoritmos heurísticos são utilizados para atribuição de comprimentos de onda, como Graph Coloring, First-Fit e Most-Used. Esta ferramenta é primeiramente testada em redes pequenas (por exemplo, topologias em anel e em malha), e depois é aplicada a redes reais (por exemplo, redes COST 239, NSFNET e UBN). Concluímos que o número de comprimentos de onda calculados para cada rede é quase independente da heurística para atribuição dos cumprimentos de onda, bem como da estratégia de ordenação dos caminhos, quando uma topologia lógica em malha completa é considerada

Cross-layer modeling and optimization of next-generation internet networks

Scaling traditional telecommunication networks so that they are able to cope with the volume of future traffic demands and the stringent European Commission (EC) regulations on emissions would entail unaffordable investments. For this very reason, the design of an innovative ultra-high bandwidth power-efficient network architecture is nowadays a bold topic within the research community. So far, the independent evolution of network layers has resulted in isolated, and hence, far-from-optimal contributions, which have eventually led to the issues today's networks are facing such as inefficient energy strategy, limited network scalability and flexibility, reduced network manageability and increased overall network and customer services costs. Consequently, there is currently large consensus among network operators and the research community that cross-layer interaction and coordination is fundamental for the proper architectural design of next-generation Internet networks. This thesis actively contributes to the this goal by addressing the modeling, optimization and performance analysis of a set of potential technologies to be deployed in future cross-layer network architectures. By applying a transversal design approach (i.e., joint consideration of several network layers), we aim for achieving the maximization of the integration of the different network layers involved in each specific problem. To this end, Part I provides a comprehensive evaluation of optical transport networks (OTNs) based on layer 2 (L2) sub-wavelength switching (SWS) technologies, also taking into consideration the impact of physical layer impairments (PLIs) (L0 phenomena). Indeed, the recent and relevant advances in optical technologies have dramatically increased the impact that PLIs have on the optical signal quality, particularly in the context of SWS networks. Then, in Part II of the thesis, we present a set of case studies where it is shown that the application of operations research (OR) methodologies in the desing/planning stage of future cross-layer Internet network architectures leads to the successful joint optimization of key network performance indicators (KPIs) such as cost (i.e., CAPEX/OPEX), resources usage and energy consumption. OR can definitely play an important role by allowing network designers/architects to obtain good near-optimal solutions to real-sized problems within practical running times