Navegando por Assunto "Elastic optical networks"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Aprovisionamento dinâmico de recursos em redes ópticas elásticas multiplexadas por divisão de espaço considerando limitações de camada física
(Universidade Federal do Pará, 2019-06-07) LOBATO, Fabricio Rossy de Lima; CARTAXO, Adolfo da Visitação Tregeira; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434
In elastic optical networks (EONs) employing weakly-coupled single-mode multi-core fibers (MCF), inter-core crosstalk (XT) can affect significantly the network performance, particularly when the number of cores and the path length increase. Hence, from the network perspective, the impairment-aware (IA) routing, spectrum and core assignment (RSCA) problem is an important research challenge of MCF-EONs. In this thesis, we propose a dynamic provisioning methodology that solves independently the IA-RSCA problem taking impairments physical layer into account. To achieve the XT impact minimization, we decompose the IA-RSCA problem into two subproblems: the IA routing sub-problem and the IA spectrum and core assignment (IA-SCA) sub-problem. For the routing solution, a precomputation method based on the k-shortest path is used, and a physical layer impairment verification phase is performed taking the required optical signal to noise ratio into account. For the IA-SCA sub-problem, the novel XT-aware greedy algorithm is proposed to minimize the XT impact on the MCF-EONs performance as follows: for each new connection, the level of detected XT power of the new connection and interfering connections relative to the XT power threshold of each connection is minimized on the average over all those connections. This minimization is achieved by choosing the core and frequency slot of the new connection. In order to take the spectral overlapping extension of the new and interfering connections into account in the detected XT power, a novel frequency slot overlapping index is introduced. The performance of the proposed algorithm is evaluated through computer simulations. The results show that the total blocking probability and network average utilization achieved by the proposed algorithm are better than the ones obtained by core prioritization, random and first-fit strategies, for different scenarios of XT level and spectrum fragmentation.
Acesso aberto (Open Access)
Políticas de alocação de espectro em roteamento baseado em balanceamento de cargas e fragmentação para redes ópticas elásticas
(Universidade Federal do Pará, 2015-02-05) DONZA, André Cunha de Sousa; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434; FRANCÊS, Carlos Renato Lisboa; http://lattes.cnpq.br/7458287841862567
The rigid nature of wavelength division multiplexing (WDM) routed networks leads to inefficient capacity utilization. Thus, flexible networks are a possible breakthrough for optical technology, as long as they provide higher spectrum efficiency use. In order to assess the possible applicability of flexible networks, this work proposes a performance evaluation strategy based on simulations and comparisons between obtained results. Several discrete-time simulations were carried out in two simulators developed in Matlab in order to analyze different spectrum allocation policies (First-Fit, Smallest-Fit, Exact-Fit and Random-Fit) in some algorithms for single path routing: The External Fragmentation Aware Assignment (FA), the Shortest Path with Maximum Spectrum Reuse (SPSR) and the Balanced Load Score Spectrum Assignment (BLSA). Two network topologies were used: a small 6-node subset of Cost239 and a 7-node random topology. With no physical layer effects as restrictions, comparisons were made between the different techniques studied, aiming to point out, based on the specific features of the proposed scenarios, the most appropriate method of spectral allocation in terms of blocking frequency between the four considered spectrum allocation policies.
Acesso aberto (Open Access)
Statistical analysis and markov modeling of dynamic resource provisioning in elastic optical networks
(Universidade Federal do Pará, 2015-06-26) ROSA, Adriana de Nazaré Farias da; CARVALHO, Solon Venâncio de; http://lattes.cnpq.br/3368137994024629; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434
The current trends in optical fiber communications are rapidly approaching the physical capacity limit of standard optical fiber. It is becoming increasingly important to efficiently utilize spectral resources wisely to accommodate the ever-increasing Internet traffic demand. However, the rigid and coarse ITU-T grid specifications regarding the spectrum usage restrict the granularity of bandwidth segmentation and allocation, which frequently causes a mismatch between the allocated and the actual requested link bandwidth. This often leads to over provisioning, where usually more resources are provided than necessary. Recently, the concept of elastic optical networks (EONs) has been proposed in order to reduce the waste of spectra resources. In networks with such feature enabled, modulation parameters and central frequencies are not fixed as in the traditional WDM networks: the resources can be allocated with fine granularity, which can adapt to the granularity of the requested bandwidth without over provisioning. This results in more efficient usage of spectral resources. However, elastic optical networks must satisfy dynamic connection add and drop over spectral resources that inevitable results in fragmentation of the spectrum. In EONs, spectrum fragmentation is an important and inevitable problem, because it reduces the spectral efficiency. As consequence, the blocking probability (BP) is increased due to scattered gaps in the optical grid. Currently, several metrics have been proposed in order to quantify a level of spectrum fragmentation. Approximation methods might be used for estimating average blocking probability and some fragmentation measures, but are so far unable to accurately evaluate the influence of different requested connection bandwidths and do not allow in-depth investigation of blocking events and their relation to fragmentation. This thesis presents the analytical study of the effect of fragmentation on requests’ blocking probability.In this study, new definitions for blocking that differentiate between the reasons for the blocking events were introduced. An analytical framework based on Markov modeling was proposed in order to calculate steady-state probabilities for the different blocking events and to analyze fragmentation related problems in elastic optical links under dynamic traffic conditions. Statistical investigations were derived in order to investigate how different allocation request sizes contribute to fragmentation and blocking probability. This work is complemented with the introduction of a new accommodated fragmentation metric that allows better differentiating between very small variations of spectrum occupancy. Moreover, we show to which extend blocking events, due to insufficient amount of available resources, become inevitable and, comparing to the amount of blocking events due to fragmented spectrum, we draw conclusions on the possible gains one can achieve by system defragmentation. We also show how efficient spectrum allocation policies really are in reducing the part of fragmentation that in particular leads to actual blocking events. Simulation experiments are carried out showing good match with our analytical results for blocking probability in a small scale scenario. Simulated blocking probabilities for the different blocking events are provided for a larger scale node- and network-wise operation scenario in elastic optical networks.