Placing regenerators in optical networks to satisfy multiple sets of requests.

The placement of regenerators in optical networks has become an active area of research during the last years. Given a set of lightpaths in a network G and a positive integer d, regenerators must be placed in such a way that in any lightpath there are no more than d hops without meeting a regenerator. While most of the research has focused on heuristics and simulations, the first theoretical study of the problem has been recently provided in [10], where the considered cost function is the number of locations in the network hosting regenerators. Nevertheless, in many situations a more accurate estimation of the real cost of the network is given by the total number of regenerators placed at the nodes, and this is the cost function we consider. Furthermore, in our model we assume that we are given a finite set of p possible traffic patterns (each given by a set of lightpaths), and our objective is to place the minimum number of regenerators at the nodes so that each of the traffic patterns is satisfied. While this problem can be easily solved when d = 1 or p = 1, we prove that for any fixed d,p ≥ 2 it does not admit a PTASUnknown control sequence '\textsc', even if G has maximum degree at most 3 and the lightpaths have length O(d)(d). We complement this hardness result with a constant-factor approximation algorithm with ratio ln (d ·p). We then study the case where G is a path, proving that the problem is NP-hard for any d,p ≥ 2, even if there are two edges of the path such that any lightpath uses at least one of them. Interestingly, we show that the problem is polynomial-time solvable in paths when all the lightpaths share the first edge of the path, as well as when the number of lightpaths sharing an edge is bounded. Finally, we generalize our model in two natural directions, which allows us to capture the model of [10] as a particular case, and we settle some questions that were left open in [10]

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

Transparent heterogeneous terrestrial optical communication networks with phase modulated signals

This thesis presents a large scale numerical investigation of heterogeneous terrestrial optical communications systems and the upgrade of fourth generation terrestrial core to metro legacy interconnects to fifth generation transmission system technologies. Retrofitting (without changing infrastructure) is considered for commercial applications. ROADM are crucial enabling components for future core network developments however their re-routing ability means signals can be switched mid-link onto sub-optimally configured paths which raises new challenges in network management. System performance is determined by a trade-off between nonlinear impairments and noise, where the nonlinear signal distortions depend critically on deployed dispersion maps. This thesis presents a comprehensive numerical investigation into the implementation of phase modulated signals in transparent reconfigurable wavelength division multiplexed fibre optic communication terrestrial heterogeneous networks. A key issue during system upgrades is whether differential phase encoded modulation formats are compatible with the cost optimised dispersion schemes employed in current 10 Gb/s systems. We explore how robust transmission is to inevitable variations in the dispersion mapping and how large the margins are when suboptimal dispersion management is applied. We show that a DPSK transmission system is not drastically affected by reconfiguration from periodic dispersion management to lumped dispersion mapping. A novel DPSK dispersion map optimisation methodology which reduces drastically the optimisation parameter space and the many ways to deploy dispersion maps is also presented. This alleviates strenuous computing requirements in optimisation calculations. This thesis provides a very efficient and robust way to identify high performing lumped dispersion compensating schemes for use in heterogeneous RZ-DPSK terrestrial meshed networks with ROADMs. A modified search algorithm which further reduces this number of configuration combinations is also presented. The results of an investigation of the feasibility of detouring signals locally in multi-path heterogeneous ring networks is also presented

A Transponder Aggregator with Efficient Use of Filtering Function for Transponder Noise Suppression

Colorless, directionless, and contentionless reconfigurable optical add/drop multiplexing (CDC-ROADM) provides highly flexible physical layer network configuration. Such CDC-ROADM must operate in multiple wavelength bands which are being increasingly implemented in optical transmission systems. The operation in C+L bands requires switch devices used in CDC-ROADM to also be capable of multiband operation. Recent studies on wavelength division multiplexing (WDM) systems have pointed out the impact of amplified spontaneous emission (ASE) noise generated by signals of different wavelengths, which causes OSNR degradation. Therefore, it is desirable to filter out the ASE noise from different transponders when multiplexing multiple wavelengths at the transmitter side, especially in a system with non-wavelength selective combiners such as directional couplers and multicast switches. The use of transponder aggregators with filtering functions, such as the M x N wavelength selective switch (WSS), is preferable for this filtering. However, the downside of these devices is that it is difficult to provide economical multiband support. Therefore, we propose an economical transponder aggregator configuration by allowing a certain amount of ASE superposition and reducing the number of filtering functions. In this paper, we fabricated a prototype of the proposed transponder aggregator by combining silica-based planar lightwave circuit technology and C+L band WSS, both commercially available, and verified its feasibility through transmission experiments. The novel transponder aggregator is a practical solution for a multiband CDC-ROADM system with improved OSNR performance.Comment: 10 pages, 11 figures. Submitted to IEEE Journal of Lightwave Technology for possible publicatio

Networking Analysis of Photonics Integrated Multiband WSS Based ROADM Architecture

Due to increasing traffic demand, the current optical transport infrastructure is experiencing capacity problems. Spa-tial Division Multiplexing (SDM) and Bandwidth Division Mul-tiplexing (BDM) have emerged as potential solutions to increase the capacity of the network infrastructure. In this paper, a novel modular photonic integrated multiband wavelength selective switch (WSS) in a reconfigurable optical add-drop multiplexer (ROADM) architecture is proposed. This proposed WSS can operate over a wide spectral range, including C+ L+S bands, and is potentially scalable to a large number of output fibers and routed channels while maintaining a small footprint. We investigated the network performance of the proposed multiband WSS switching structure in the Spain-E topology network and performed a detailed comparison for the SDM and BDM sce-narios. In comparison to the SDM approach, which requires the deployment of additional fibers, the results show that the cost-effective BDM scenario can utilize the capacity better without installing the new fiber infrastructure or using dark fibers

Minimizing equipment and energy cost in mixed 10G and 100G/200G filterless horseshoe networks with hierarchical OTN boards

Emerging 5G services are changing the way operators manage and optimize their optical metro networks, and the transmission technology and network design process must be tailored to the specific conditions in this segment of the network. Ensuring cost-efficient and energy-efficient network design requires novel approaches that optimize across all network layers. Therefore, to moderate the growth of operators’ expenses, in this paper, we investigate low-cost and energy-efficient cross-layer deployment of hierarchical optical transport network (OTN) boards minimizing equipment and energy consumption cost in mixed 10G and 100G/200G filterless metro networks. We propose an integer linear programming (ILP) model and a genetic algorithm (GA) approach that decide: (i) the node structure by deploying various stacked OTN boards (performing traffic-grooming at the electrical layer) and (ii) lightpath establishment considering coherent and non-coherent transmission technologies. Simulative results on real filterless horseshoe networks with real traffic matrices show that our proposed approaches achieve up to 50% cost savings compared to real-world benchmark deployments

Tunable Holographic Components in WDM Optical Networks

This paper describes the applications of a multipurpose holographic device in optical networks with Coarse and Dense Wavelength Division Multiplexing (CWDM/ DWDM) technologies. In its basic structure, it can operate as a tunable wavelength filter, wavelength multiplexer or λ router. By using a more complex structure, the device works as OADM (Optical Add Drop Multiplexer) or OS (Optical Switch). Some simulations of the basic devices, from the optical transmission point of view, are made to match the transmission parameters for the application in optical networks. Performance parameters of the device, like switching time, losses, cross-talk or polarization insensitivity are analyzed and compared with other multiplexing or switching technologies. To complete the review of these components, a study of computer generated holograms (CGH) design is carried out. The results are used in the design of holographic devices to perform different applications: in Metro networks, where a design of a holographic device with wavelength conversion and routing is analyzed, or, in Access Networks like a tunable filter or demultiplexer in Fiber to the Home/Business (FTTH/FTTB) topologies