Core optical networks using reconfigurable optical switches and tunable lasers appear to be on the road towards widespread deployment and could evolve to all-optical mesh networks in the coming future. Considering the impact of physical layer impairments in the planning and operation of all-optical (and translucent) networks is the main focus of the Dynamic Impairment Constraint Optical Networking (DICONET) project. The impairment aware network planning and operation tool (NPOT) is the main outcome of DICONET project, which is explained in detail in this paper. The key building blocks of the NPOT, consisting of network description repositories, the physical layer performance evaluator, the impairment aware routing and wavelength assignment engines, the component placement modules, failure handling, and the integration of NPOT in the control plane are the main contributions of this study. Besides, the experimental result of DICONET proposal for centralized and distributed control plane integration schemes and the performance of the failure handling in terms of restoration time is presented in this study.

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Experimental Demonstration of an Impairment Aware Network Planning and Operation Tool for Transparent/Translucent Optical Networks

Numerous Routing and Wavelength Assignment (RWA) algorithms have been developed these last ten years for WDM optical networks planning. In most cases, these algorithms neglect the impact of physical layer impairments on the feasibility of the obtained optical circuits or lightpaths. In this paper, we introduce a new quality of transmission (QoT) dependent tool called LERP (Lightpath Establishment with Regenerator Placement) enabling to solve the RWA problem in guaranteeing the feasibility of the obtained solution. The LERP tool tends to minimize the amount of rejected lightpath demands due to a lack of network resources. Network resources correspond to the amount of available wavelengths in each fiber-link. A lightpath is said admissible if BER at its destination node remains under a given threshold. In case on BER non-admissibility, one or several electrical regenerators may be inserted along the lightpath. The first originality of our approach consists in minimizing simultaneously the amount of rejected traffic demands and the amount of required regenerators. For that purpose, one considers a much larger combinatoric in lightpaths’ selection and regenerators’ placement. The second originality of the LERP tool relies on BER evaluation in considering simultaneously chromatic dispersion, polarization mode dispersion, amplified spontaneous emission and non-linear phase shift. The efficiency of the LERP heuristic is underlined via a numerical comparison with one of the alternative solutions proposed in the literature in the context of the NSFNET network.

http://service.tsi.telecom-paristech.fr/cgi-bin/valipub_download.cgi?dId=7

LERP : a Quality of Transmission Dependent Heuristic for Routing and Wavelength Assignment in Hybrid WDM Networks LERP : une heuristique pour le routage et l'affectation de longueurs d'onde tenant compte de la qualité de transmission dans les réseaux WDM hybrides

In translucent optical networks, the physical layer impairments degrading the optical signal are considered in the network planning In this paper, we investigate the offline problem of routing and wavelength assignment (RWA) and regenerator placement (RP) in translucent networks, minimizing the lightpath blocking and regenerator equipment cost We address two variants of the problem, which correspond to two different types of quality of transmission (QoT) estimators, called linear and nonlinear In a nonlinear QoT, nonlinear impairments like crosstalk or cross-phase modulation, which account for the interferences from neighboring lightpaths in the network are explicitly computed Then, the QoT estimated for a lightpath depends on the routes of other lightpaths in the network In the linear QoT, the effects of the nonlinear impairments are overestimated and accumulated to the rest of the impairments in the QoT calculation As a result, the QoT estimation of a lightpath solely depends on its route For the linear case, we formulate an optimal integer linear programming model of the problem, to the best of the authors' knowledge, for the first time in the literature Its simplicity allows us to test it for small- and medium-size networks Also, we propose two heuristic methods, namely, lightpath segmentation and three-step, and a tight lower bound for the regenerator equipment cost For the nonlinear QoT case, we propose a new heuristic called iterative RP (IRP) Both the IRP and three-step algorithms are designed to guarantee that no lightpath blocking is produced by signal degradation This is a relevant difference with respect to earlier proposals The performance and the scalability of our proposals are then investigated by carrying out extensive tests Results reveal that the solutions obtained by the heuristic algorithms are optimal or close to optimal, and outperform the earlier proposals in the literature

/pdf/offline-impairment-aware-rwa-and-regenerator-placement-in-4bbi16g8i3.pdf

Offline Impairment-Aware RWA and Regenerator Placement in Translucent Optical Networks

In the last 15 years, numerous investigations by both academia and industry have been carried out in the field of all-optical WDM networks' design. In all-optical - or transparent - WDM networks, data is transmitted from its source to its destination in optical form, switching/routing operations being performed in the optical domain without undergoing any optical-to-electrical conversion. Optical transparency may considerably reduce network infrastructures' cost and extend the range of services offered by the carriers. Designing an all-optical network consists of assigning to each traffic demand an endto- end optical circuit, also called "lightpath." In such networks, the problem of routing and wavelength assignment (RWA) aims to find an adequate route and an adequate wavelength for each traffic demand subject to the wavelength continuity constraint and limited network resources. The feasibility of the obtained lightpaths in terms of admissible quality of transmission (QoT) presents another difficulty. Indeed, according to the state of technology, various physical impairments degrade the quality of the optical signal along its propagation. Optical fibers and optical amplifiers as well as optical switching/routing nodes impact on end-to-end QoT. In this context only translucent networks are achievable, for instance, at a pan-European or pan-American scale. A translucent network uses electrical regenerators at intermediate nodes only when it is necessary to improve the signal budget. The cost of a network is roughly proportional to average number of input/output ports of a node. Knowing that today an optical port is five times less expensive than an electrical one, sparse regeneration allows translucent WDM networks to meet the QoT requirements and achieve performance measures close to those obtained by fully opaque networks at much lower cost. In this article we propose a state of the art in the field of impairment-aware RWA (IA-RWA), starting from the case of predictable traffic demands to the open problem of stochastic traffic demands. An economic analysis of the IA-RWA problem is proposed to justify the concept of translucent networks. The case of multi-domain lightpath establishment is also considered. Several examples of still open problems are mentioned in the article. Most of the concepts and results presented in this article refer to the FP7 DICONET European project in which the authors are involved.

Impairment-aware routing and wavelength assignment in translucent networks: State of the art

In modern communication network unwanted failures occurred. A design of robust network is required to handle the failures, restore the failed part and maintain the traffic flow of the network within a permissible time frame, at the lowest cost. The next-generation (5G) communication and computing networks, software-defined networks and internet-of-things networks assures to provide high speeds, impressive data rates and remarkable reliability. We need to design complex and robust next generation networks that must be built with minimum failure possibilities, quick failure recovery capabilities and high network restoration capacity. Therefore, improved network restoration models are needs to be developed and incorporated. In this paper, a comprehensive study on network restoration mechanisms that are being developed for addressing network failures in current and next generation (5G) networks is carried out. Open-ended problems are identified, while invaluable ideas for better adaptation of network restoration to evolving 5G communication and computing models are discussed.

Restoration of the Network for Next Generation (5G) Optical Communication Network

In the absence of all-optical 3R regenerators, the quality of transmission has a strong impact of the feasibility of all-optical long-haul transmission. Four main physical layer impairments degrade the quality of an optical analog signal, namely chromatic dispersion (CD), polarization mode dispersion (PMD), optical signal to noise ratio (OSNR), and nonlinear phase shift (PhiNL). In most previous studies, a Q factor evaluates the quality of transmission in considering the aforementioned parameters individually (Qi with i isin {1,2,3,4}). In this paper, we propose a tool implementing a global Q factor that takes into account the interaction between the four impairments and from which we derive the bit error rate (BER). This new factor referenced as Q8 enables to study the suitability of optical transparency in transport networks. By means of numerical applications, we compare two backbone networks: the North-American NSF network (NSFNET) and the Pan-European backbone (EBN)

Physical layer impairments in WDM core networks: a comparison between a North-American backbone and a Pan-European backbone

Many studies have been carried out in the field of translucent network design during the last years Translucent networks use sparse regeneration strategy where electrical regeneration is performed at a limited number of network nodes in order to improve the signal budget The objective of translucent network design is to judiciously choose the regeneration sites to overcome the signal degradation and to maintain a predefined quality of transmission Pachnicke et al have recently proposed an approach for routing and regenerator placement In this paper, we propose a novel heuristic called COR2P for translucent network design Our concern is both to minimize the number of required regenerators and to concentrate them in a limited number of sites In addition, we propose an improved version of Pachnicke's algorithm under the name of RP-CBR+ and we proceed to the comparison of these two approaches On one hand, both COR2P and RP-CBR+ choose, a priori, a set of regeneration sites, before the effective RWA phase Our approach is both traffic and topology-driven since it considers the effective traffic matrix and the limited capacity of the network Oppositely, regeneration sites placement in RP-CBR+ is only topology-driven since it considers a connection demand between any pair of nodes under unlimited network capacity On the other hand, COR2P differs from RP-CBR+ in three points: the order in which traffic demands are processed, the wavelength assignment strategy and the possibility or not to use additional regeneration sites Simulation results show that unlike RP-CBR+, COR2P accepts all traffic demands under low traffic load, using the same number of regenerators Under high traffic load, our algorithm presents much lower blocking ratios than RP-CBR+ at the price of a larger number of regenerators

Traffic-Driven vs. Topology-Driven Strategies for Regeneration Sites Placement

Most studies carried out in the field of RWA in WDM networks assume an ideal optical medium. However, throughout its route an optical signal undergoes many transmission impairments introduced by long-haul optical components. In all-optical WDM networks, where no electrical 3R regeneration is performed at intermediate nodes, transmission impairments accumulate and may result in high BER values at the receiverpsilas side. Hybrid WDM networks use sparse regeneration to overcome transmission impairments. Such networks achieve performance measures close to those obtained by fully opaque networks at a much lesser cost. In previous work, we addressed the problem of hybrid WDM network design by proposing a tool for routing, wavelength assignment and regenerator placement so that the physical constraints are taken into account. A standard First-Fit scheme is performed for the wavelength assignment problem. In recent work, we proposed a QoT-aware wavelength assignment strategy that considerably improves the performance achieved by our tool. In this paper, we propose a new wavelength assignment strategy called Best-BER-Fit. The Best-BER-Fit strategy chooses the first available wavelength that guarantees the quality of transmission required to establish the lightpath. The studied strategy is compared to the First-Fit and Min-BER-Fit strategies in terms of the number of required regenerators.

Impact of wavelength assignment strategies on hybrid WDM network planning

The evolution of optical network devices such as optical cross-connects and optical amplifiers has provided a huge increase in the transmission capacity of optical links. However, this evolution also brings problems such as the large power imbalance arising with the transmission of several wavelengths that imposes a severe degradation to the optical signal. Recent research work shows how to adapt all-optical (transparent) WDM networks to cope with transmission impairments induced by long-haul optical components on long spans. Since no electrical 3R regeneration is performed at intermediate nodes in a transparent network, transmission impairments accumulate along the signal route and may result in high BER values at the receiver's side. Since they provide sparse regeneration, hybrid WDM networks are considered as a promising solution to overcome the transmission impairments and achieve performance measures close to those obtained by fully opaque networks at a much lesser cost. In previous work, we addressed the design of hybrid WDM network and proposed a novel tool for routing, wavelength assignment, and regenerator placement so that the quality of transmission is guaranteed. Up to now, we did not consider any in-line gain equalization scheme, i.e. dynamic gain equalizers are only deployed at the network nodes. In this paper, we investigate the impact of deploying in-line dynamic gain equalizers in terms of the number of required regenerators to meet QoT and in terms of cost tradeoff. We also propose a novel wavelength assignment strategy that takes into account the quality of transmission. Simulations show that using an adequate QoT-aware wavelength assignment strategy may compensate for the absence of in-line equalization.

Gain Equalization versus Electrical Regeneration Tradeoffs in Hybrid WDM Networks

A centralized impairment-aware lightpath restoration scheme is experimentally demonstrated. Through the implementation of the QoT estimator module on FPGA technology, restoration times of 1.36s are achieved for the high priority traffic class.

S. Al Zahr

Papers

Physical layer impairments in WDM core networks: a comparison between a North-American backbone and a Pan-European backbone

Traffic-Driven vs. Topology-Driven Strategies for Regeneration Sites Placement

Impact of wavelength assignment strategies on hybrid WDM network planning

Gain Equalization versus Electrical Regeneration Tradeoffs in Hybrid WDM Networks

Experimental evaluation of centralized failure restoration in a dynamic impairment-aware all-optical network