Efficient Wavelength Assignment Technique for the Reduction of Blocking Probability in WDM/DWDM Network

Viewing on the rising demand and keeping eye on the expected future market of telecommunication industry, now a days all the service providers are much more focused on the efficiency part of their network system. The technique of routing and wavelength assignment (RWA) in a WDM/DWDM network is closely related to the performance of the network and ultimately the efficiency of the entire network system is based on it. Where, all the service providers trying hard to maintain a satisfactory level of transmission quality, there various types of physical layer impairments are obstacles for them. This research work proposes a technique for the reduction of four-wave mixing (FWM) effect by using an efficient RWA scheme for WDM/DWDM networks. However, we have gone through numbers of RWA schemes from various literature and found those are less efficient to provide better quality of transmission. In this thesis, we have proposed a WA scheme which partitions the entire fiber transmission window into ’N’ number of bands and assigns wavelength randomly from any one of the band based on connection length. Finally, the analytical result proves that, this mechanism reduces the FWM effect significantly which is computed in terms of blocking probability. It says higher the partition, lower the FWM effect

On the performance of M-QAM optical signals in ROADM based optical networks

The optical network physical layer limitations, in particular, the crosstalk due to imperfect isolation of optical network switching components, such as Reconfigurable Optical Add/Drop Multiplexers (ROADMs), can become a limiting factor in the performance of these networks. In this work, the impact of in-band crosstalk due to M-ary quadrature amplitude modulation (M-QAM) interferers on the performance of 4-QAM and 16-QAM coherent receivers in ROADM based networks is analysed, using Monte Carlo (MC) simulation. Several Wavelength Select Switch (WSS) models, a ROADM component, were studied, and each WSS model had a different optical filter profile. Two crosstalk metrics, unweighted crosstalk and weighted crosstalk, are used to measure the system performance degradation regarding the Optical Signal-to-Noise Ratio (OSNR) penalty at the coherent receiver. The difference between the two, is the fact that weighted crosstalk takes into account that the spectrum content closer to the center of the channel bandwidth has more impact than spectral content closer to the edges of the channel bandwidth. Using unweighted crosstalk metric, it can be concluded that optical filters with a wider rejection bandwidth in the center of the channel, have a better performance in terms of OSNR penalty at the coherent receiver. With the weighted crosstalk metric, it was observed that regardless of the WSS filter profile, the OSNR penalty performances of each WSS were similar. It can be concluded that the weighted crosstalk metric is very reliable at predicting system performances independently of the filter shape present in the WSS.As limitações do nivel físico das redes ópticas, nomeadamente a diafonia (crosstalk) devido ao isolamento imperfeito de elementos de redes de fibra óptica, como os Multiplexadores Ópticos de Adição/Extracção Reconfiguráveis (ROADMs), podem constituir um factor limitativo no desempenho das redes ópticas. Nesta dissertação, foi estudado através de simulação de Monte-Carlo (MC), o impacto do crosstalk homódino devido a sinais interferentes com o formato de modulação em amplitude e em quadratura (M-QAM), no desempenho dos receptores coerentes de sinais 4-QAM e 16-QAM. Foram também estudados vários Selectores de Comprimento de Onda (WSS), um componente dos ROADMs, e em que cada WSS tem um filtro óptico com um perfil diferente. Duas métricas de crosstalk, unweighted crosstalk e weighted crosstalk, foram usadas para estudar a degradação do desempenho do sistema de comunicações ópticas referente à relação de sinal-ruído óptica (OSNR), no receptor coerente. A diferença entre estas duas métricas, é o facto de o weighted crosstalk levar em consideração que o conteúdo espectral perto do centro da largura de banda do canal, tem um impacto maior do que o conteúdo espectral perto das margens da largura de banda do canal. Analisando os resultados com a métrica unweighted crosstalk, foi possível concluir que WSSs com filtros ópticos com a banda de rejeição maior e mais centrada com a largura de banda do canal, obtiveram melhor desempenho em relação à penalidade de OSNR medida no receptor coerente. Usando o weighted crosstalk como métrica, foi observado que todos os WSSs registaram desempenhos semelhantes em termos de penalidade de OSNR. Podemos concluir, que o weighted crosstalk constitui uma métrica bastante fiável a prever desempenhos de sistemas de comunicações ópticos, independentemente do perfil dos filtros usados em cada WSS

Impact of physical layer impairments on SDM networks based on ROADM nodes

Current transport optical networks are approaching its capacity limits, mainly due to new applications and services that require a huge amount of resources. To increase the network capacity, multiband solutions, that exploit the unused capacity of actual fibers, in particular the L-band, are being currently commercially explored. However, this strategy is assumed as a short to medium term solution. A long-term solution is to use spatial-division multiplexing (SDM) in the optical domain, which leads to the concept of SDM-based optical networks. In this work, different SDM switching architectures (spatial, spatial-wavelength, wavelength, fractional space-full wavelength) are studied and compared in terms of cost per bit, power consumption and flexibility. For the switching architectures with spatial and spatial-wavelength granularities (the architectures that have superior performance), the most relevant physical impairments (PLIs) (amplifiers noise, non-linear interference, narrowing penalty due to filtering and in-band crosstalk) are analytically studied, for a SDM reconfigurable optical add-drop multiplexer (ROADM) cascade. Furthermore, a Monte Carlo simulation is used to assess more rigorously the PLIs effects on the performance of SDM ROADMs, with spatial-wavelength switching architecture, in cascade. The main difference, regarding PLIs, between the single spatial channel ROADM architecture and the SDM ROADM architectures is the enhanced effect of in-band crosstalk. For cascaded ROADMs with 16 directions, 19 spatial channels and filtering isolation of -25 dB, the in-band crosstalk can lead to a 2 dB optical signal-to-noise ratio penalty. Due to this penalty, the signal crosses less 9 ROADMs than in a single spatial channel ROADM architecture.As redes óticas de transporte atuais estão a aproximar-se do seu limite de capacidade devido às novas aplicações e serviços que requerem uma maior quantidade de recursos de rede. Uma possível solução de curto a médio prazo para a falta de recursos é o uso de múltiplas bandas da fibra, para além da banda C. Uma solução a longo prazo será o uso de multiplexagem com divisão no espaço (SDM) no domínio óptico. Neste trabalho são estudados, o custo por bit, consumo de energia e flexibilidade, das diferentes arquiteturas SDM (no espaço, no espaço e comprimento de onda, no comprimento de onda, fracionada no espaço e completa no comprimento de onda). Para as arquiteturas com granularidades no espaço e no espaço e comprimento de onda estuda-se analiticamente os efeitos das principais limitações do nível físico (PLIs) (ruído dos amplificadores, interferência não-linear, penalidade de filtragem e diafonia homódina), para cascatas de multiplexadores óticos de inserção/extração reconfiguráveis (ROADMs). Usa-se uma simulação Monte Carlo para calcular mais rigorosamente os efeitos das PLIs na arquitetura com granularidade no espaço e comprimento de onda. A principal diferença, em termos de PLIs, entre uma rede SDM e uma rede com um único canal espacial é o efeito da diafonia homódina. Para uma rede com 16 direções, 19 canais espaciais e isolamento dos filtros de -25 dB, a diafonia homódina causa uma penalidade na relação sinal-ruído óptica de 2 dB e o sinal atravessa menos 9 ROADMs que numa rede com apenas um canal espacial

Performance of translucent optical networks under dynamic traffic and uncertain physical-layer information

This paper investigates the performance of translucent Optical Transport Networks (OTNs) under different traffic and knowledge conditions, varying from perfect knowledge to drifts and uncertainties in the physical-layer parameters. Our focus is on the regular operation of a translucent OTN, i.e., after the dimensioning and regenerator placement phase. Our contributions can be summarized as follows. Based on the computation of the Personick’s Q factor, we introduce a new methodology for the assessment of the optical signal quality along a path, and show its application on a realistic example. We analyze the performance of both deterministic and predictive RWA techniques integrating this signal quality factor Q in the lightpath computation process. Our results confirm the effectiveness of predictive techniques to deal with the typical drifts and uncertainties in the physical-layer parameters, in contrast to the superior efficacy of deterministic approaches in case of perfect knowledge. Conversely to most previous works, where all wavelengths are assumed to have the same characteristics, we examine the case when the network is not perfectly compensated, so the Maximum Transmission Distance (MTD) of the different wavelength channels may vary. We show that blocking might increase dramatically when the MTD of the different wavelength channels is overlooked.Postprint (published version

Impact of physical layer impairments on multi-band metro networks

The traffic increase in optical metro networks will saturate the network capacity in a near future, mainly due to new cloud and 5G services, as well as to an increasing number of network users. The use of other fiber bands, than the usual C-band, is seen as a possible near term solution, for this probable capacity crunch. In this work, a metro network horseshoe topology with nodes capable of switching both C and L-band signals is studied. In particular, we have considered for switching Cband signals, reconfigurable optical add/drop multiplexer and Filterless Drop and Waste (FD&W) node architectures, whereas for switching L-band signals, we have considered only FD&W solutions, both amplified and unamplified. An analytical formalism was developed to assess the impact of the physical layer impairments due to fiber transmission and switching node in a horseshoe network performance. Moreover, the cost and power consumption of the C-band and L-band nodes are analyzed. We concluded that in a network end of life scenario, the L-band nodes cost is 3.5 times higher than the C-band nodes, being 99% of this cost attributed to the transponders. In L-band transmission, a lightpath can cross several spans with 10 or 60 km in the amplified solution. In the unamplified solution, where frequency reuse is allowed, a lightpath consists only on a single 10 km span due to the maximum optical link budget. Considering a -20 dB crosstalk level, a 1.5 dB degradation on the optical power budget is observed.O aumento de tráfego nas redes metropolitanas irá saturar a capacidade das redes num futuro próximo, principalmente devido aos novos serviços em nuvem e 5G, bem como ao aumento do número de utilizadores. O uso de novas bandas na fibra ótica, além da banda C, é visto como uma possível solução para responder a esse aumento de capacidade. Neste trabalho, é apresentada a topologia de rede ”horseshoe”, que contém nós com capacidade para comutar sinais nas bandas C e L. Na banda C, consideram-se as arquiteturas com multiplexadores de inserção/extração reconfiguráveis e arquiteturas sem filtragem, e na banda L, consideram-se apenas soluções sem filtragem, com e sem amplificação. São estudadas, analiticamente, as limitações físicas da transmissão na fibra e comutação dos sinais nos nós da rede ”horseshoe”. Além disso, é realizado um estudo do custo, consumo e capacidade dos nós nas bandas C e L. Num cenário de fim de vida da rede, o custo dos nós na banda L é 3.5 vezes superior aos da banda C. O custo dos transponders constitui 99% do custo final. Na banda L, o sinal pode atravessar várias secções de 10 ou 60 km na solução amplificada. Na solução não amplificada, onde existe reuso de frequência, só há uma secção de 10 km devido ao orçamento máximo de potência na ligação. Para um nível de diafonia de -20 dB, o orçamento de potência diminui 1.5 dB

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

The Effects of Optimized Regenerator Allocation in Trans-lucent Networks under Inaccurate Physical information

Optimized regenerator allocation techniques select which of the already installed regenerators in a translucent network must be used in order to maximize the quality of the optical signal while minimizing the opaqueness of the network. Unfortunately, the performance of an optimized regenerator allocation strategy strongly depends on the accuracy of the physical-layer information. In this paper, we investigate the effects of optimized regenerator allocation techniques when the physical-layer information is inaccurate. According to the performed experiments, we conclude that mostly of the current techniques of regenerator usage optimization are only possible when perfect knowledge of physical information is available. Hence, new regenerator allocation schemes taking into account the inherent inaccuracy in the physical-layer information need to be designed.Postprint (published version