Study of Routing and Wavelength Assignment problem and Performance Analysis of Genetic Algorithm for All-Optical Networks

All-optical networks uses the concept of wavelength division multiplexing (WDM). The problem of routing and wavelength assignment (RWA) is critically important for increasing the efficiency of wavelength routed All-optical networks. For the given set of connections, the task of setting up lightpaths by routing and assigning a wavelength to each connection is called routing and wavelength allocation problem. In work to date, the problem has been formulated as integer linear programming problem. There are two variations of the problem: static and dynamic, in the static case, the traffic is known where as in dynamic case, connection request arrive in some random fashion. Here we adopt the static view of the problem. We have studied the Genetic Algorithm to solve the RWA problem and also we studied a modified Genetic Algorithm with reference to the basic model. We studied a novel opimization problem formulations that offer the promise of radical improvements over the existing methods. We adopt a static view of the problem and saw new integer- linear programming formulations, which can be addressed with highly efficient linear programming methods and yield optimal or near-optimal RWA policies. All-optical WDM networks are chracterized by multiple metrics (hop-count, cost, delay), but generally routing protocols only optimize one metric, using some variant shortest path algorithm (e.g., the Dijkstra, all-pairs and Bellman-ford algorithms). The multicriteria RWA problem has been solved combining the relevant metrics or objective functions. The performance of RWA algorithms have been studied across the different standard networks. The performance of both the algorithms are studied with respect to the time taken for making routing decision, number of wavelengths required and cost of the requested lightpaths. It has been observed that the modified genetic algorithm performed better than the existing algorithm with respect to the time and cost parameters

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

Rerouting Enhancements For Single-layer Traffic Grooming

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2007Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2007İnternetin hızla büyümesi, veri iletim kapasitesi ihtiyacını arttırmaktadır. Bu ihtiyacı karşılamak için, optik taşıyıcılar metal kabloların yerini almaktadır. Bir optik taşıyıcının yüksek bant genişliğinden, dalga boyu bölümlemeli çoğullama tekniği (WDM) ile yararlanılmaktadır. Bir WDM optik ağda, optik taşıyıcı bağlantıları fiziksel topolojiyi meydana getirir. Optik çapraz bağlarla (OXC) birbirine bağlanan dalga boylarından oluşan yollara ışık yolu denir. Bir optik ağda kurulmuş tüm ışık yolları, sanal topolojiyi oluşturur. Optik ağ üzerinde yönlendirme yapmak, ışık yollarının fiziksel topoloji üzerinden yönlendirilmesi ve bağlantı isteklerinin ışık yolları üzerinden yönlendirilmesi alt problemlerini içerir; iki-katmanlı yönlendirme problemidir. Yönlendirme problemi iki katmanda ayrı ayrı çözülebileceği gibi (iki katmanlı çözüm), bütünleşik olarak da ele alınabilir (tek katmanlı çözüm). Bir dalga boyu kanalının kapasitesi, bir bağlantı isteğinin bant genişliği ihtiyacına göre çok yüksektir. Ağ kaynaklarını verimli kullanabilmek için, yüksek hızlı ışık yollarının bant genişliğini, düşük hızlı bağlantı isteklerine paylaştırmak gerekmektedir. Bu yönteme trafik “grooming” denir. Bu çalışmada, dinamik bağlantı istekleri için tasarlanmış, grooming yeteneğini de hesaba katan mevcut tek katmanlı yönlendirme çözümlerinden biri seçilerek kullanılmıştır. Bağlantıları tekrar yönlendirerek ağ kaynaklarının verimli kullanılması konusu, dinamik trafik için yaygın olarak işlenmiş bir konu değildir. Ayrıca, dinamik trafik için önerilen yeniden yönlendirme algoritmaları yeni yolların sanal katmanda aranmasına yoğunlaşmaktadır. Bu da yönlendirmenin tek katmanda ele alındığı çözümlere uygun bir yaklaşım değildir. Bu çalışmada, dinamik bağlantı istekleri için trafik grooming sorununun tek katmanlı çözümüne uygun yeniden yönlendirme yöntemleri önerilmiştir.Fast growth of internet traffic increases the demand for data transmission capacity. Optical fibers are replacing the metal wires, to meet the increasing demand. An optical fiber’s huge bandwidth capacity is exploited by Wavelength Division Multiplexing (WDM) technique. In an optical WDM network, optical fiber links form the physical topology. Paths of wavelengths connected to each other by optical cross connects (OXCs) are called lightpaths. All the lightpaths established in an optical network constitute the virtual topology. Routing connections in an optical network involves sub problems of routing the lightpaths over physical topology and routing the connections over the lightpaths; thus is a two-layer routing problem. Routing problem can be solved in two layers separately (two-layer solutions) or jointly (single-layer solutions). There exists a large a gap between the capacity of a WDM channel and the bandwidth requirement of a connection request. In order to use the network resources efficiently, low-speed traffic connections need to be multiplexed onto high-speed lightpaths. This method is referred to as traffic grooming. In this study, an existing single-layer routing solution for dynamic traffic requests, which considers traffic grooming, was applied. Rerouting connections to utilize network resources efficiently has not been widely considered for dynamic traffic conditions. Furthermore, rerouting algorithms proposed for dynamic traffic perform new path search on virtual layer. This approach is not suitable for single-layer routing solutions. In this study, rerouting enhancements for single-layer solution of traffic grooming under dynamic traffic conditions were proposed.Yüksek LisansM.Sc

Optical network cost reduction techniques bases on multiple modulation formats

Orientadores: Darli Augusto de Arruda Mello, Miquel Garrich AlabarceDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A utilização de redes ópticas elásticas viabiliza o melhor aproveitamento da infraestrutura óptica já instalada, possibilitando a acomodação da demanda crescente de tráfego. Esta tecnologia combina transceptores de banda variável e arquiteturas de nós de rede flexíveis, baseados em chaves seletoras de comprimento de onda, em um sistema capaz de rotear sinais heterogêneos. Os transceptores de banda variável permitem o ajuste de seus parâmetros de forma a variar formato de modulação, taxa de símbolo e taxa de bit da transmissão de acordo com as restrições impostas pelo canal de comunicação e dispositivos da rede. Contudo, as altas potências necessárias para transmissões de longas distâncias (e o consequente aumento de não-linearidades) e a baixa imunidade ao ruído dos formatos de modulação de altas ordens, são dois importantes desafios a serem superados. De fato, é tema de pesquisa emergente a busca por algoritmos de compensação de não-linearidades de baixa complexidade computacional. Neste trabalho, analisamos duas técnicas de redução de custo da rede baseadas nos múltiplos formatos de modulação proporcionados pelas redes elásticas. As duas técnicas são complementares à complexa compensação não-linear. A primeira técnica é a formatação probabilística que, alterando a probabilidade de envio dos símbolos da constelação, permite o aumento da capacidade de um formato de modulação de alta ordem mantendo-se a energia média do sinal transmitido. A segunda técnica é conhecida por arquitetura sob demanda, na qual os nós da rede óptica são sintetizados de acordo com a demanda por tráfego. No caso da formatação probabilística, observou-se um ganho superior ao da compensação não-linear intracanal perfeita, com uma economia no número médio de transceptores utilizados de até 6,7% analisando-se dados experimentais. Os resultados indicam que a formatação probabilística pode muitas vezes substituir a compensação não-linear, reduzindo significativamente a complexidade computacional do receptor. Já no caso da arquitetura sob demanda, observou-se um aumento da taxa de bit média transmitida por canal para baixas cargasAbstract: The deployment of elastic optical networking is able to extend the lifetime of already deployed optical fibers to accommodate the ever-increasing network traffic demand. This technology combines bandwidth-variable transponders and wavelength selective switch-based nodes with flexible architectures in a system capable of routing heterogeneous signals. Bandwidth-variable transponders can adjust their modulation format, symbol and code rates according to constraints imposed by the communication channel and network devices. However, the nonlinearities generated at the high power levels required by long-distance transmission, and the low tolerance to noise of high-order modulation formats, are two important factors that limit the optical transmission reach. Accordingly, low-complexity signal processing for the compensation of nonlinearities is an active research field. In this work, we analyze two network cost reduction techniques based on multiple modulation formats enabled by elastic optical networks. Both techniques are complementary to non-linear compensation. The first technique is probabilistic shaping, which increases the capacity of communications systems by changing the transmission probability of constellation symbols, while maintaining the average transmitted power. The second technique is known as architecture on demand (AoD), by which optical network nodes are synthetized according to the traffic demand. The results indicate that probabilistic shaping outperforms ideal intrachannel non-linear compensation for a full-spectrum occupation. Our framework, based on theoretical derivations and experimental data analysis, showed to be possible do reduce the average number of transceivers per link in up to 6.7%. In addition, probabilistic shaping replaced non-linear compensation in various scenarios, considerably decreasing the computational complexity at the receiver. The results on AoD, in turn, showed to be possible to increase the average bit rate per channel for low traffic loadMestradoTelecomunicações e TelemáticaMestra em Engenharia Elétric

Reconfigurations of Logical Topologies for WDM Mesh Networks

In static lightpath allocation, the logical topology of a WDM mesh network is determined, based on the long-term traffic demands. These traffic demands change with time. When a logical topology is incapable of supporting the current traffic demands, the logical topology has to be changed. The change is made by adding a minimum number of edges to the logical topology. The objective of this research is to find an optimal new Logical Topology which can support the current traffic demands with as little change to the existing topology as possible. We have proposed a Hill-Climbing algorithm to solve the reconfiguration problem of logical topologies in WDM networks. Our problem can be divided into two sub-problems. The first is to find an optimal logical topology and the second is to route the traffic optimally on the logical topology. Keywords: Optical Networks, Mesh Networks, WDM Networks, Optimization, Logical Topology, Reconfiguration, Heuristic

Dynamic Optical Networks for Data Centres and Media Production

This thesis explores all-optical networks for data centres, with a particular focus on network designs for live media production. A design for an all-optical data centre network is presented, with experimental verification of the feasibility of the network data plane. The design uses fast tunable (< 200 ns) lasers and coherent receivers across a passive optical star coupler core, forming a network capable of reaching over 1000 nodes. Experimental transmission of 25 Gb/s data across the network core, with combined wavelength switching and time division multiplexing (WS-TDM), is demonstrated. Enhancements to laser tuning time via current pre-emphasis are discussed, including experimental demonstration of fast wavelength switching (< 35 ns) of a single laser between all combinations of 96 wavelengths spaced at 50 GHz over a range wider than the optical C-band. Methods of increasing the overall network throughput by using a higher complexity modulation format are also described, along with designs for line codes to enable pulse amplitude modulation across the WS-TDM network core. The construction of an optical star coupler network core is investigated, by evaluating methods of constructing large star couplers from smaller optical coupler components. By using optical circuit switches to rearrange star coupler connectivity, the network can be partitioned, creating independent reserves of bandwidth and resulting in increased overall network throughput. Several topologies for constructing a star from optical couplers are compared, and algorithms for optimum construction methods are presented. All of the designs target strict criteria for the flexible and dynamic creation of multicast groups, which will enable future live media production workflows in data centres. The data throughput performance of the network designs is simulated under synthetic and practical media production traffic scenarios, showing improved throughput when reconfigurable star couplers are used compared to a single large star. An energy consumption evaluation shows reduced network power consumption compared to incumbent and other proposed data centre network technologies

Efficient Spectrum Utilization in Large-Scale RWA and RSA Problems

While the Routing and Wavelength Assignment (RWA) problem has been widely studied, very few studies attempt to solve realistic size instances, namely, with 100 wavelengths per fiber and a few hundred nodes. Indeed, state of the art is closer to around 20 nodes and 30 wavelengths. In this study, we are interested in reducing the gap between realistic data sets and testbed instances, using exact methods. We propose different algorithms that lead to solve exactly or near exactly much larger instances than in the literature, with up to 150 wavelengths and 90 nodes. Extensive numerical experiences are conducted on both the static and the dynamic cases. For the latter, we investigate how much bandwidth is wasted when no lightpath re-arrangement is allowed, and compare it with the number of lightpath re-arrangement it requires in order to fully maximize the grade of service. Results show that the amount of lightpath re-arrangement remains very small in comparison to the amount of wasted bandwidth if not done. The Routing and Spectrum Assignment (RSA) problem is a much more difficult problem than RWA, considered in elastic optical networks. Although investigated extensively, there is still a gap between the size of the instances that can be solved using the current heuristic or exact algorithms, and the size of the instances arising in the industry. As the second objective of this study, we aim to reduce the gap between the two, using a new mathematical modeling, and compare its performance with the best previous algorithms/models on realistic data instances

Dynamic Wavelength Allocation in All-Optical Ring Networks

We focus on wavelength allocation schemes for all-optical WDM ring networks. For an N node network we characterize the traffic by its load L (the maximum number of lightpaths that share a link) and do not assume knowledge of the arrival/departure processes. We prove that shortest path routing produces a routing which has at most twice the load of the optimal solution. We show that at least 0:5L log 2 N wavelengths are required by any algorithm in the worst case, and develop an algorithm which requires up to 3L log 2 N wavelengths. For the case when the load is high and blocking is necessary we present an improved algorithm. Technical Subject Area: Optical communications This work was supported in part by grant MDA 972-95-C-0001 from ARPA. A preliminary version of this paper was published as an IBM research report no. RC20462, May Dynamic Wavelength Allocation in All-Optical Ring Networks, O. Gerstel and S. Kutten 1 1 Introduction 1.1 Background As WDM systems start emerging from ..