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

Reconfigurable optical networks with dynamic physical impairments

Orientador: Helio WaldmanDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: As redes ópticas reconfiguráveis compõem o backbone de grande parte das redes de transporte em operação ao redor do mundo. No entanto, os desafios para ampliar a capacidade e eficiência destas redes ainda são enormes. Com objetivo de maximizar a carga útil de tráfego suportada nas redes ópticas WDM reconfiguráveis é de fundamental importância adotar eficientes algoritmos RWA. Os algoritmos RWA são responsáveis pela escolha adequada de recursos na rede para provisionar novas conexões de forma a maximizar a probabilidade de atendimento das futuras conexões. Nesta dissertação, o problema RWA será investigado sob diversas novas perspectivas através de um ambiente de simulação. Com a preocupação de retratar os reais problemas vivenciados pelas redes ópticas reconfiguráveis, os elementos de rede foram modelados de acordo com as tecnologias e arquiteturas atualmente empregadas no mercado. No caso dos elementos de comutação ROADM e amplificadores EDFA, serão adotadas modelagens ainda não exploradas na literatura relacionada ao problema RWA. Diversos estudos abordam o problema RWA levando em consideração as degradações de camada física na escolha dos recursos apropriados para o provisionamento de novas conexões. Esta abordagem é conhecida na literatura como RWA-IA. Neste trabalho será adotada uma abordagem mais realista, considerando não apenas as condições de camada física para o provisionamento de novas conexões, mas também o impacto na camada física causado pelo estabelecimento de novas conexões nas demais já ativas na rede. Ainda neste trabalho serão propostos dois novos algoritmos de alocação de comprimento de onda sensíveis às degradações dinâmicas da camada física. Um extenso estudo com a avaliação de desempenho destes algoritmos será realizado, contemplando também um estudo comparativo com outros algoritmos encontrados na literatura e utilizados com frequência no mercado. Os algoritmos propostos demonstraram excelente desempenho, conseguindo inclusive superar o desempenho dos demais algoritmos avaliados em termos de probabilidade de bloqueioAbstract: Reconfigurable optical networks has been adopted as the backbone solution by most of transport networks around the world. However, in order to expand the capacity and efficiency of these networks, there are still many challenges to overcome. In order to improve the reconfigurable optical network capacity is very important to work with efficient RWA algorithms capable to find appropriate network resources for new lightpaths and, at the same, to minimize the blocking probability of future demands. In this dissertation, the RWA problem will be investigated under several new perspectives through a simulation environment. Committed to retract real problems experienced by reconfigurable optical networks, network elements were design according to the technologies and architectures currently employed in the industry. The ROADM switching elements and EDFA amplifiers were design in an unprecedented way in the RWA literature. Several studies addressing the RWA problem have already incorporated the physical layer impairments in order to find the appropriate resources for establishing new lightpaths. This approach has become known in the literature as Impairment Aware RWA (IA-RWA). In this dissertation, we adopted a more realistic approach to the RWA-IA problem, also considering the impact on the physical layer caused by the establishment of new connections in the others already established in the network. Moreover, in this work we will propose two new wavelength assignment algorithms aware to the physical layer dynamic impairments. An extensive performance evaluation study about these algorithms will be performed, also contemplating a comparative study with other algorithms from the literature and widely used in the industry. The proposed new algorithms have shown excellent performance, outperforming other algorithms evaluated in terms of blocking probabilityMestradoTelecomunicações e TelemáticaMestre em Engenharia Elétric

Monitoring of passive optical networks utilising an optical coding technique

Passive Optical Networks (PONs) have become the most popular fibre based access networks over the last decade. They are widely deployed for use in Fibre-to-the-Premises (FTTP) scenarios. PON is a point-to-multipoint connection (P2MP) between an optical line terminal (OLT) located at the central office (CO) and multiple optical network units (ONU) at the customer premises. The next generation of PONs (NG-PON) are likely to deploy a ring-and-spur long reach PON (LR-PON). NG-PON aims to accommodate more ONUs, extend the network coverage out to 100 km, minimize complexity and improve operational outcomes. An all fibre access network, operating over extended distances, presents a reliability risk, thereby increasing the need for a reliable and cost-effective monitoring system to enhance protection and reduce restoration time. Among existing monitoring techniques, attention is focused on approaches that use optical code division multiplexing (OCDM), also known as optical coding (OC). The OC is applied to a signal that is sent from the network management system (NMS) to the ONUs. The monitoring signal is transmitted onto a fibre and split into a number of sub-signals that are equal in number to the ONUs. Each one of the ONUs receives a sub-signal, encodes it, and then reflects it back to the NMS. The NMS has the capability to identify faulty ONUs by examining the code received from the ONUs. A review of the literature has shown that the use of OCs does improve system performance, especially in the timely detection of faults. Many of the studies, found in the literature, focus on how to implement optical spreading codes that are used in OCDM Access (OCDMA) systems and currently the optical orthogonal code (OOC) is the dominant code implemented for time-domain coding. Although the OOC code performs well, its construction is relatively complex. The available code-words (cardinality) that are offered by OOC are proportional to the code length. Implementing OOC in a high capacity PON requires a long code length causes an inevitable degradation of system performance. Therefore, an improved optical coding technique for PONs should provide code-words that conform to PON split ratios. The main objective of the research was to develop an optical spreading code, based on a prime code family for OCDMA systems, that has the capability to accommodate different PON split ratios and with characteristics that improve transmission system performance when compared to existing prime code families. The novel code presented in this thesis is identified as the extended grouped new modified prime code (EG-nMPC). The number of code-words generated by the proposed codes are substantially higher than those generated by the existing code families and more compatible to the different PON splitting ratios. In addition, with a low code weight, both power consumption and hardware complexity decreases. The code performance was evaluated using mathematical models for two transmission formats - pulse position modulation (PPM) and on-off keying (OOK) modulation. The performance of EG-nMPC was compared to other prime codes, and the results show that the proposed code improves the performance of OCDMA in terms of bit-error rate (BER). As PON is a point-to-multipoint connection oriented access network, downstream traffic is encrypted and broadcast to all ONUs, while the unencrypted upstream traffic from each ONU terminal occurs in a burst mode. The OLT carries out a ranging process to determine transmission delays between ONUs, to prevent collisions between the burst mode traffic from each of the ONUs. In this research, the burst mode traffic ranging process has been replicated in the monitoring system, with this replication providing a fixed equalization delay time for the monitoring transmissions. To investigate the ring-and-spur LR-PON reliability several protection architectures were evaluated, in term of cost and availability, to determine the optimal protection architecture. In this thesis, the reliability parameter Failure Impact Robustness (FIR), has been used to calculate the failure impact of the different components in ring-and-spur LR-PON, hence selecting the optimal protection scheme. A PON-based optical communication system model was developed and the proposed EG-nMPC code was incorporated. Fibre split ratios of 32, 64 and 128, were considered in this study. The simulation results show that the EG-nMPC code improves the performance, efficiency and accuracy of the PON transmission monitoring system. To conclude, this research aims to enhance the PON performance by a fast detection of the fault and quick restoration. This research has contributed to knowledge by identifying a new and novel spreading code that is compatible with the different PON splitting ratios for OC monitoring techniques. By using the ranging process, a fixed equalization delay time has been assigned to each ONU to manage the upstream burst traffic. The spreading code has been implemented in a real-time simulation to show the status of each fibre link. The implementation was carried out based on 1-D tree topology system. However, the proposed EG-nMPC can be exploited to enable network monitoring that is based on hybrid 1D/2D coding. This coding is complementary with the structure of LR-PON as explained in section ‎8.2.3. In addition, with the use of the FIR parameter for the different components in the ring-and-spur architecture, an optimal protection scheme for both OLT and the ring (feeder fibre), has been nominated. This protection scheme ensures that protection, availability and cost are at their optimal values

Optical flow switched networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (p. 253-279).In the four decades since optical fiber was introduced as a communications medium, optical networking has revolutionized the telecommunications landscape. It has enabled the Internet as we know it today, and is central to the realization of Network-Centric Warfare in the defense world. Sustained exponential growth in communications bandwidth demand, however, is requiring that the nexus of innovation in optical networking continue, in order to ensure cost-effective communications in the future. In this thesis, we present Optical Flow Switching (OFS) as a key enabler of scalable future optical networks. The general idea behind OFS-agile, end-to-end, all-optical connections-is decades old, if not as old as the field of optical networking itself. However, owing to the absence of an application for it, OFS remained an underdeveloped idea-bereft of how it could be implemented, how well it would perform, and how much it would cost relative to other architectures. The contributions of this thesis are in providing partial answers to these three broad questions. With respect to implementation, we address the physical layer design of OFS in the metro-area and access, and develop sensible scheduling algorithms for OFS communication. Our performance study comprises a comparative capacity analysis for the wide-area, as well as an analytical approximation of the throughput-delay tradeoff offered by OFS for inter-MAN communication. Lastly, with regard to the economics of OFS, we employ an approximate capital expenditure model, which enables a throughput-cost comparison of OFS with other prominent candidate architectures. Our conclusions point to the fact that OFS offers significant advantage over other architectures in economic scalability.(cont.) In particular, for sufficiently heavy traffic, OFS handles large transactions at far lower cost than other optical network architectures. In light of the increasing importance of large transactions in both commercial and defense networks, we conclude that OFS may be crucial to the future viability of optical networking.by Guy E. Weichenberg.Ph.D

Analytic modelling and resource dimensioning of optical burst switched networks

The realisation of optical network architectures may hold the key to delivering the enormous bandwidth demands of next generation Internet applications and services. Optical Burst Switching (OBS) is a potentially cost-effective switching technique that can satisfy these demands by offering a high bit rate transport service that is bandwidth-efficient under dynamic Internet traffic loads. Although various aspects of OBS performance have been extensively investigated, there remains a need to systematically assess the cost/performance trade-offs involved in dimensioning OBS switch resources in a network. This goal is essential in enabling the future deployment of OBS but poses a significant challenge due to the complexity of obtaining tractable mathematical models applicable to OBS network optimisation. The overall aim of this thesis lies within this challenge. This thesis firstly develops a novel analytic performance model of an OBS node where burst contention is resolved by combined use of Tuneable Wavelength Converters (TWCs) and Fibre Delay Lines (FDLs) connected in an efficient share-per-node configuration. The model uses a two-moment traffic representation that gives a good trade-off between accuracy and complexity, and is suitable for extension to use in network modelling. The OBS node model is then used to derive an approximate analytic model of an OBS network of switches equipped with TWCs and FDLs, again maintaining a two-moment traffic model for each end-to-end traffic path in the network. This allows evaluation of link/route loss rates under different offered traffic characteristics, whereas most OBS network models assume only a single-moment traffic representation. In the last part of this thesis, resource dimensioning of OBS networks is performed by solving single and multi-objective optimisation problems based on the analytic network model. The optimisation objectives relate to equipment cost minimisation and throughput maximisation under end-to-end loss rate constraints. Due to non-convexity of the network performance constraint equations, a search heuristic approach has been taken using a constraint-handling genetic algorithm