A tabu search heuristic for routing in WDM networks.

Optical networks and Wavelength-Division Multiplexing (WDM) have been widely studied and utilized in recent years. By exploiting the huge bandwidth of optical networks, WDM appears to be one of the most promising technologies to meet the dramatically increased demand for bandwidth. Since optical resources in optical networks are very expensive, development of dynamic lightpath allocation strategies, which utilize network resource efficiently, is an important area of research. We assume that there is no optical wavelength conversion device in the network, and the wavelength-continuity constraint must be satisfied. Exact optimization techniques are typically too time-consuming to be useful for practical-sized networks. In this thesis we present a tabu search based heuristic approach which is used to establish an optimal lightpath dynamically in response to a new communication request in a WDM network. As far as we know, this is the first investigation using tabu search techniques for dynamical lightpath allocation in WDM networks. We have tested our approach with networks having different sizes. And then we have compared our results with those obtained using the MILP approach. In the vast majority of cases, tabu search was able to quickly generate a solution that was optimal or near-optimal, indicating that tabu search is a promising approach for the dynamic lightpath allocation problem in WDM networks. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .W36. Source: Masters Abstracts International, Volume: 43-01, page: 0247. Advisers: Subir Bandyopadhyay; Arunita Jaekel. Thesis (M.Sc.)--University of Windsor (Canada), 2004

Reconfigurable nodes for passive optical networks (PON)

Mestrado em Engenharia Electrónica e TelecomunicaçõesRecentemente , as redes ópticas de nova geração têm sido motivo de acesa discussão nos meios científicos. Com o aumento verificado nos últimos anos do numero de utilizadores e o aparecimento de novos serviços disponibilizados através das redes de acesso, torna-se cada vez mais claro que a fibra óptica é a única solução para disponibilizar a largura de banda necessária. Neste trabalho é apresentado um novo método passivo capaz de aumentar os níveis de escalabilidade e reconfigurabilidade destas redes. O método consiste no controlo da quantidade de potência de bomba entregue a um amplificador ou conjunto de amplificadores remotos em série, permitindo o controlo independentemente do ganho fornecido por cada amplificador. Utilizando o método proposto consegue-se evitar o uso de componentes activos, ou mais complexos, para controlo da quantidade de potência de bomba a fornecer aos amplificadores remotos, tornando o processo de amplificação simultaneamente passivo e reconfigurável. Foi também desenvolvido, no âmbito deste trabalho, uma ferramenta de simulação baseada em algoritmos genéticos, capaz de simular e determinar a melhor solução para diversos cenários, optimizando os diversos parâmetros. Foi também realizada a caracterização de uma fibra óptica dopada com érbio, onde foi estudado o comportamento do ganho da fibra dopada quando bombeada por um sinal de bomba diferente dos comprimentos de onda nominais, 980nm e 1480nm. Ainda, o caso de bombeamentos com diferentes comprimentos de onda multiplexados foi motivo de estudo. ABSTRACT: Recently, the new generation optical networks are being the focus of several discussions in the scientific forums. With the observed increase of users in the last years, and the emergence of new services supplied through the access networks, it became even clearer that optical fiber is the best solution to provide the required bandwidth. In this work it is presented a new passive method capable to improve the scalability and reconfigurability of those networks. The method consist in controlling the amount of pump power to be supplied to one or various remotely pumped optical amplifiers disposed in series, and by this, adjust independently the gain of each. Using the proposed method, it is possible to dismiss the use of active or/and complex components, to control the remote amplifiers conditions, making all this amplification process passive and reconfigurable. It was also developed during this work, a simulation tool based in genetic algorithms, capable to simulate and reach the best solution for different network scenarios, optimizing the several parameters. A laboratory characterization of an erbium doped fiber amplifier it was also performed, where it was studied the gain behaviour of the doped fiber, when it is pumped by a signal which wavelength is different of the nominal wavelengths, 980nm and 1480nm. In this characterization it was also studied the gain behaviour when the amplifier is pumped with multiple multiplexed pump signals

Particle swarm optimization for routing and wavelength assignment in next generation WDM networks.

PhDAll-optical Wave Division Multiplexed (WDM) networking is a promising technology for long-haul backbone and large metropolitan optical networks in order to meet the non-diminishing bandwidth demands of future applications and services. Examples could include archival and recovery of data to/from Storage Area Networks (i.e. for banks), High bandwidth medical imaging (for remote operations), High Definition (HD) digital broadcast and streaming over the Internet, distributed orchestrated computing, and peak-demand short-term connectivity for Access Network providers and wireless network operators for backhaul surges. One desirable feature is fast and automatic provisioning. Connection (lightpath) provisioning in optically switched networks requires both route computation and a single wavelength to be assigned for the lightpath. This is called Routing and Wavelength Assignment (RWA). RWA can be classified as static RWA and dynamic RWA. Static RWA is an NP-hard (non-polynomial time hard) optimisation task. Dynamic RWA is even more challenging as connection requests arrive dynamically, on-the-fly and have random connection holding times. Traditionally, global-optimum mathematical search schemes like integer linear programming and graph colouring are used to find an optimal solution for NP-hard problems. However such schemes become unusable for connection provisioning in a dynamic environment, due to the computational complexity and time required to undertake the search. To perform dynamic provisioning, different heuristic and stochastic techniques are used. Particle Swarm Optimisation (PSO) is a population-based global optimisation scheme that belongs to the class of evolutionary search algorithms and has successfully been used to solve many NP-hard optimisation problems in both static and dynamic environments. In this thesis, a novel PSO based scheme is proposed to solve the static RWA case, which can achieve optimal/near-optimal solution. In order to reduce the risk of premature convergence of the swarm and to avoid selecting local optima, a search scheme is proposed to solve the static RWA, based on the position of swarm‘s global best particle and personal best position of each particle. To solve dynamic RWA problem, a PSO based scheme is proposed which can provision a connection within a fraction of a second. This feature is crucial to provisioning services like bandwidth on demand connectivity. To improve the convergence speed of the swarm towards an optimal/near-optimal solution, a novel chaotic factor is introduced into the PSO algorithm, i.e. CPSO, which helps the swarm reach a relatively good solution in fewer iterations. Experimental results for PSO/CPSO based dynamic RWA algorithms show that the proposed schemes perform better compared to other evolutionary techniques like genetic algorithms, ant colony optimization. This is both in terms of quality of solution and computation time. The proposed schemes also show significant improvements in blocking probability performance compared to traditional dynamic RWA schemes like SP-FF and SP-MU algorithms

Investigation of the tolerance of wavelength-routed optical networks to traffic load variations.

This thesis focuses on the performance of circuit-switched wavelength-routed optical network with unpredictable traffic pattern variations. This characteristic of optical networks is termed traffic forecast tolerance. First, the increasing volume and heterogeneous nature of data and voice traffic is discussed. The challenges in designing robust optical networks to handle unpredictable traffic statistics are described. Other work relating to the same research issues are discussed. A general methodology to quantify the traffic forecast tolerance of optical networks is presented. A traffic model is proposed to simulate dynamic, non-uniform loads, and used to test wavelength-routed optical networks considering numerous network topologies. The number of wavelengths required and the effect of the routing and wavelength allocation algorithm are investigated. A new method of quantifying the network tolerance is proposed, based on the calculation of the increase in the standard deviation of the blocking probabilities with increasing traffic load non-uniformity. The performance of different networks are calculated and compared. The relationship between physical features of the network topology and traffic forecast tolerance is investigated. A large number of randomly connected networks with different sizes were assessed. It is shown that the average lightpath length and the number of wavelengths required for full interconnection of the nodes in static operation both exhibit a strong correlation with the network tolerance, regardless of the degree of load non-uniformity. Finally, the impact of wavelength conversion on network tolerance is investigated. Wavelength conversion significantly increases the robustness of optical networks to unpredictable traffic variations. In particular, two sparse wavelength conversion schemes are compared and discussed: distributed wavelength conversion and localized wavelength conversion. It is found that the distributed wavelength conversion scheme outperforms localized wavelength conversion scheme, both with uniform loading and in terms of the network tolerance. The results described in this thesis can be used for the analysis and design of reliable WDM optical networks that are robust to future traffic demand variations

Design and provisioning of WDM networks for traffic grooming

Wavelength Division Multiplexing (WDM) is the most viable technique for utilizing the enormous amounts of bandwidth inherently available in optical fibers. However, the bandwidth offered by a single wavelength in WDM networks is on the order of tens of Gigabits per second, while most of the applications\u27 bandwidth requirements are still subwavelength. Therefore, cost-effective design and provisioning of WDM networks require that traffic from different sessions share bandwidth of a single wavelength by employing electronic multiplexing at higher layers. This is known as traffic grooming. Optical networks supporting traffic grooming are usually designed in a way such that the cost of the higher layer equipment used to support a given traffic matrix is reduced. In this thesis, we propose a number of optimal and heuristic solutions for the design and provisioning of optical networks for traffic grooming with an objective of network cost reduction. In doing so, we address several practical issues. Specifically, we address the design and provisioning of WDM networks on unidirectional and bidirectional rings for arbitrary unicast traffic grooming, and on mesh topologies for arbitrary multipoint traffic grooming. In multipoint traffic grooming, we address both multicast and many-to-one traffic grooming problems. We provide a unified frame work for optimal and approximate network dimensioning and channel provisioning for the generic multicast traffic grooming problem, as well as some variants of the problem. For many-to-one traffic grooming we propose optimal as well as heuristic solutions. Optimal formulations which are inherently non-linear are mapped to an optimal linear formulation. In the heuristic solutions, we employ different problem specific search strategies to explore the solution space. We provide a number of experimental results to show the efficacy of our proposed techniques for the traffic grooming problem in WDM networks

Towards An Optimal Core Optical Network Using Overflow Channels

This dissertation is based on a traditional circuit switched core WDM network that is supplemented by a pool of wavelengths that carry optical burst switched overflow data. These overflow channels function to absorb channel overflows from traditional circuit switched networks and they also provide wavelengths for newer, high bandwidth applications. The channel overflows that appear at the overflow layer as optical bursts are either carried over a permanently configured, primary light path, or over a burst-switched, best-effort path while traversing the core network. At every successive hop along the best effort path, the optical bursts will attempt to enter a primary light path to its destination. Thus, each node in the network is a Hybrid Node that will provide entry for optical bursts to hybrid path that is made of a point to point, pre-provisioned light path or a burst switched path. The dissertation's main outcome is to determine the cost optimality of a Hybrid Route, to analyze cost-effectiveness of a Hybrid Node and compare it to a route and a node performing non-hybrid operation, respectively. Finally, an example network that consists of several Hybrid Routes and Hybrid Nodes is analyzed for its cost-effectiveness. Cost-effectiveness and optimality of a Hybrid Route is tested for its dependency on the mean and variance of channel demands offered to the route, the number of sources sharing the route, and the relative cost of a primary and overflow path called path cost ratio. An optimality condition that relates the effect of traffic statistics to the path cost ratio is analytically derived and tested. Cost-effectiveness of a Hybrid Node is compared among different switching fabric architecture that is used to construct the Hybrid Node. Broadcast-Select, Benes and Clos architectures are each considered with different degrees of chip integration. An example Hybrid Network that consists of several Hybrid Routes and Hybrid Nodes is found to be cost-effective and dependent of the ratio of switching to transport costs