A new ILP-based p-cycle construction algorithm without candidate cycle enumeration

The notion of p-cycle (Preconfigured Protection Cycle) allows capacity efficient schemes to be designed for fast span protection in WDM mesh networks. Conventional p-cycle construction algorithms need to enumerate/pre-select candidate cycles before ILP (Integer Linear Program) can be applied. In this paper, we propose a new algorithm which is only based on ILP. When the required number of p-cycles is not too large, our ILP can generate optimal/suboptimal solutions in reasonable amount of running time. © 2007 IEEE.published_or_final_versio

Link failure protection and restoration in WDM optical networks

In a wavelength-division-multiplexing (WDM) optical network, the failure of fiber links may cause the failure of multiple optical channels, thereby leading to large data loss. Therefore the survivable WDM optical networks where the affected traffic under link failure can be restored, have been a matter of much concern. On the other hand, network operators want options that are more than just survivable, but more flexible and more efficient in the use of capacity. In this thesis, we propose our cost-effective approaches to survive link failures in WDM optical networks. Dynamic establishment of restorable connections in WDM networks is an important problem that has received much study. Existing algorithms use either path-based method or link-based method to protect a dynamic connection; the former suffers slow restoration speed while the latter requires complicated online backup path computation. We propose a new dynamic restorable connection establishment algorithm using p-cycle protection. For a given connection request, our algorithm first computes a working path and then computes a set of p-cycles to protect the links on the working path so that the connection can survive any single link failure. The key advantage of the proposed algorithm over the link-based method is that it enables faster failure restoration while requires much simpler online computation for connection establishment. Tree-based schemes offer several advantages such as scalability, failure impact restriction and distributed processing. We present a new tree-based link protection scheme to improve the hierarchical protection tree (p-tree) scheme [31] for single link failure in mesh networks, which achieves 100% restorability in an arbitrary 2-connected network. To minimize the total spare capacity for single link failure protection, an integer linear programming (ILP) formulation is provided. We also develop a fast double-link failure restoration scheme by message signaling to take advantage of the scalable and distributed processing capability of tree structure

ILP formulations for p-cycle design without candidate cycle enumeration

The concept of p-cycle (preconfigured protection cycle) allows fast and efficient span protection in wavelength division multiplexing (WDM) mesh networks. To design p-cycles for a given network, conventional algorithms need to enumerate cycles in the network to form a candidate set, and then use an integer linear program (ILP) to find a set of p-cycles from the candidate set. Because the size of the candidate set increases exponentially with the network size, candidate cycle enumeration introduces a huge number of ILP variables and slows down the optimization process. In this paper, we focus on p-cycle design without candidate cycle enumeration. Three ILPs for solving the problem of spare capacity placement (SCP) are first formulated. They are based on recursion, flow conservation, and cycle exclusion, respectively. We show that the number of ILP variables/constraints in our cycle exclusion approach only increases linearly with the network size. Then, based on cycle exclusion, we formulate an ILP for solving the joint capacity placement (JCP) problem. Numerical results show that our ILPs are very efficient in generating p-cycle solutions. © 2009 IEEE.published_or_final_versio

Advanced flight control system study

The architecture, requirements, and system elements of an ultrareliable, advanced flight control system are described. The basic criteria are functional reliability of 10 to the minus 10 power/hour of flight and only 6 month scheduled maintenance. A distributed system architecture is described, including a multiplexed communication system, reliable bus controller, the use of skewed sensor arrays, and actuator interfaces. Test bed and flight evaluation program are proposed

Differentiated quality-of-recovery and quality-of-protection in survivable WDM mesh networks

In the modern telecommunication business, there is a need to provide different Quality-of-Recovery (QoR) and Quality-of-Protection (QoP) classes in order to accommodate as many customers as possible, and to optimize the protection capacity cost. Prevalent protection methods to provide specific QoS related to protection are based on pre-defined shape protection structures (topologies), e.g., p -cycles and p -trees. Although some of these protection patterns are known to provide a good trade-off among the different protection parameters, their shapes can limit their deployment in some specific network conditions, e.g., a constrained link spare capacity budget and traffic distribution. In this thesis, we propose to re-think the design process of protection schemes in survivable WDM networks by adopting a hew design approach where the shapes of the protection structures are decided based on the targeted QoR and QoP guarantees, and not the reverse. We focus on the degree of pre-configuration of the protection topologies, and use fully and partially pre-cross connected p -structures, and dynamically cross connected p -structures. In QoR differentiation, we develop different approaches for pre-configuring the protection capacity in order to strike different balances between the protection cost and the availability requirements in the network; while in the QoP differentiation, we focus on the shaping of the protection structures to provide different grades of protection including single and dual-link failure protection. The new research directions proposed and developed in this thesis are intended to help network operators to effectively support different Quality-of-Recovery and Quality-of-Protection classes. All new ideas have been translated into mathematical models for which we propose practical and efficient design methods in order to optimize the inherent cost to the different designs of protection schemes. Furthermore, we establish a quantitative relation between the degree of pre-configuration of the protection structures and their costs in terms of protection capacity. Our most significant contributions are the design and development of Pre-Configured Protection Structure (p-structure) and Pre-Configured Protection Extended-Tree (p -etree) based schemes. Thanks to the column generation modeling and solution approaches, we propose a new design approach of protection schemes where we deploy just enough protection to provide different quality of recovery and protection classe

Scalable Column Generation Models and Algorithms for Optical Network Planning Problems

Column Generation Method has been proved to be a powerful tool to model and solve large scale optimization problems in various practical domains such as operation management, logistics and computer design. Such a decomposition approach has been also applied in telecommunication for several classes of classical network design and planning problems with a great success. In this thesis, we confirm that Column Generation Methodology is also a powerful tool in solving several contemporary network design problems that come from a rising worldwide demand of heavy traffic (100Gbps, 400Gbps, and 1Tbps) with emphasis on cost-effective and resilient networks. Such problems are very challenging in terms of complexity as well as solution quality. Research in this thesis attacks four challenging design problems in optical networks: design of p-cycles subject to wavelength continuity, design of dependent and independent p-cycles against multiple failures, design of survivable virtual topologies against multiple failures, design of a multirate optical network architecture. For each design problem, we develop a new mathematical models based on Column Generation Decomposition scheme. Numerical results show that Column Generation methodology is the right choice to deal with hard network design problems since it allows us to efficiently solve large scale network instances which have been puzzles for the current state of art. Additionally, the thesis reveals the great flexibility of Column Generation in formulating design problems that have quite different natures as well as requirements. Obtained results in this thesis show that, firstly, the design of p-cycles should be under a wavelength continuity assumption in order to save the converter cost since the difference between the capacity requirement under wavelength conversion vs. under wavelength continuity is insignificant. Secondly, such results which come from our new general design model for failure dependent p-cycles prove the fact that failure dependent p-cycles save significantly spare capacity than failure independent p-cycles. Thirdly, large instances can be quasi-optimally solved in case of survivable topology designs thanks to our new path-formulation model with online generation of augmenting paths. Lastly, the importance of high capacity devices such as 100Gbps transceiver and the impact of the restriction on number of regeneration sites to the provisioning cost of multirate WDM networks are revealed through our new hierarchical Column Generation model

Optimization of p-cycle protection schemes in optical networks

La survie des réseaux est un domaine d'étude technique très intéressant ainsi qu'une préoccupation critique dans la conception des réseaux. Compte tenu du fait que de plus en plus de données sont transportées à travers des réseaux de communication, une simple panne peut interrompre des millions d'utilisateurs et engendrer des millions de dollars de pertes de revenu. Les techniques de protection des réseaux consistent à fournir une capacité supplémentaire dans un réseau et à réacheminer les flux automatiquement autour de la panne en utilisant cette disponibilité de capacité. Cette thèse porte sur la conception de réseaux optiques intégrant des techniques de survie qui utilisent des schémas de protection basés sur les p-cycles. Plus précisément, les p-cycles de protection par chemin sont exploités dans le contexte de pannes sur les liens. Notre étude se concentre sur la mise en place de structures de protection par p-cycles, et ce, en supposant que les chemins d'opération pour l'ensemble des requêtes sont définis a priori. La majorité des travaux existants utilisent des heuristiques ou des méthodes de résolution ayant de la difficulté à résoudre des instances de grande taille. L'objectif de cette thèse est double. D'une part, nous proposons des modèles et des méthodes de résolution capables d'aborder des problèmes de plus grande taille que ceux déjà présentés dans la littérature. D'autre part, grâce aux nouveaux algorithmes, nous sommes en mesure de produire des solutions optimales ou quasi-optimales. Pour ce faire, nous nous appuyons sur la technique de génération de colonnes, celle-ci étant adéquate pour résoudre des problèmes de programmation linéaire de grande taille. Dans ce projet, la génération de colonnes est utilisée comme une façon intelligente d'énumérer implicitement des cycles prometteurs. Nous proposons d'abord des formulations pour le problème maître et le problème auxiliaire ainsi qu'un premier algorithme de génération de colonnes pour la conception de réseaux protegées par des p-cycles de la protection par chemin. L'algorithme obtient de meilleures solutions, dans un temps raisonnable, que celles obtenues par les méthodes existantes. Par la suite, une formulation plus compacte est proposée pour le problème auxiliaire. De plus, nous présentons une nouvelle méthode de décomposition hiérarchique qui apporte une grande amélioration de l'efficacité globale de l'algorithme. En ce qui concerne les solutions en nombres entiers, nous proposons deux méthodes heurisiques qui arrivent à trouver des bonnes solutions. Nous nous attardons aussi à une comparaison systématique entre les p-cycles et les schémas classiques de protection partagée. Nous effectuons donc une comparaison précise en utilisant des formulations unifiées et basées sur la génération de colonnes pour obtenir des résultats de bonne qualité. Par la suite, nous évaluons empiriquement les versions orientée et non-orientée des p-cycles pour la protection par lien ainsi que pour la protection par chemin, dans des scénarios de trafic asymétrique. Nous montrons quel est le coût de protection additionnel engendré lorsque des systèmes bidirectionnels sont employés dans de tels scénarios. Finalement, nous étudions une formulation de génération de colonnes pour la conception de réseaux avec des p-cycles en présence d'exigences de disponibilité et nous obtenons des premières bornes inférieures pour ce problème.Network survivability is a very interesting area of technical study and a critical concern in network design. As more and more data are carried over communication networks, a single outage can disrupt millions of users and result in millions of dollars of lost revenue. Survivability techniques involve providing some redundant capacity within the network and automatically rerouting traffic around the failure using this redundant capacity. This thesis concerns the design of survivable optical networks using p-cycle based schemes, more particularly, path-protecting p-cycles, in link failure scenarios. Our study focuses on the placement of p-cycle protection structures assuming that the working routes for the set of connection requests are defined a priori. Most existing work carried out on p-cycles concerns heuristic algorithms or methods suffering from critical lack of scalability. Thus, the objective of this thesis is twofold: on the one hand, to propose scalable models and solution methods enabling to approach larger problem instances and on the other hand, to produce optimal or near optimal solutions with mathematically proven optimality gaps. For this, we rely on the column generation technique which is suitable to solve large scale linear programming problems. Here, column generation is used as an intelligent way of implicitly enumerating promising cycles to be part of p-cycle designs. At first, we propose mathematical formulations for the master and the pricing problems as well as the first column generation algorithm for the design of survivable networks based on path-protecting p-cycles. The resulting algorithm obtains better solutions within reasonable running time in comparison with existing methods. Then, a much more compact formulation of the pricing problem is obtained. In addition, we also propose a new hierarchical decomposition method which greatly improves the efficiency of the whole algorithm and allows us to solve larger problem instances. As for integer solutions, two heuristic approaches are proposed to obtain good solutions. Next, we dedicate our attention to a systematic comparison of p-cycles and classical shared protection schemes. We perform an accurate comparison by using a unified column generation framework to find provably good results. Afterwards, our study concerns an empirical evaluation of directed and undirected link- and path-protecting p-cycles under asymmetric traffic scenarios. We show how much additional protection cost results from employing bidirectional systems in such scenarios. Finally, we investigate a column generation formulation for the design of p-cycle networks under availability requirements and obtain the first lower bounds for the problem

Solar dynamic power system development for Space Station Freedom

The development of a solar dynamic electric power generation system as part of the Space Station Freedom Program is documented. The solar dynamic power system includes a solar concentrator, which collects sunlight; a receiver, which accepts and stores the concentrated solar energy and transfers this energy to a gas; a Brayton turbine, alternator, and compressor unit, which generates electric power; and a radiator, which rejects waste heat. Solar dynamic systems have greater efficiency and lower maintenance costs than photovoltaic systems and are being considered for future growth of Space Station Freedom. Solar dynamic development managed by the NASA Lewis Research Center from 1986 to Feb. 1991 is covered. It summarizes technology and hardware development, describes 'lessons learned', and, through an extensive bibliography, serves as a source list of documents that provide details of the design and analytic results achieved. It was prepared by the staff of the Solar Dynamic Power System Branch at the NASA Lewis Research Center in Cleveland, Ohio. The report includes results from the prime contractor as well as from in-house efforts, university grants, and other contracts. Also included are the writers' opinions on the best way to proceed technically and programmatically with solar dynamic efforts in the future, on the basis of their experiences in this program