A Multi-Objective ILP Formulation for RWA Problem in WDM Networks

All-optical networks employing Wavelength Division Multiplexing (WDM) technique will be the backbone of next generation Internet. In WDM optical networks, each fiber link is logically divided into multiple non-interfering, circuit-switched communication channels known as avelength channels and are identified by the length of the wave.Routing and Wavelength Assignment (RWA) problem is a classical problem in WDM networks. It is further divided into two subproblems: (i) Routing, and (ii)Wavelength Assignment. Routing subproblem finds a route fromsource to destination.Wavelength Assignment subproblem assigns a wavelength to the route established byrouting subproblem. The RWA problem is combinatorial by its nature and belongs to a class of dicult combinatorial optimization problems. The optimal solution to the RWA problem is found to be NP-complete and thus suited to heuristic approaches. RWAproblem is reported in the current literature as an integer linear programming problem (ILP) that typically optimizes a single objective, either minimizes the number amplifiers, the network load or maximizes the number of connections while satisfying power constraints. In this work, we formulated the RWA problem as a multi objective ILP problem. Our primary concern is to establish a loop free lightpath that is immune to signal distortion and crosstalk. An attempt is made to obtain a feasible solution using genetic algorithm (GA). The parameters considered for optimization are congestion among the individual lightpath requests, connection set up time, the number of intermediate hops traversed and the number of fibers used to honor the established connection requests. We onsidered ARPANET (Advanced Research Project Agency NETwork) and NSFNET (National Science Foundation NETwork) for our simulation

Cross-layer modeling and optimization of next-generation internet networks

Scaling traditional telecommunication networks so that they are able to cope with the volume of future traffic demands and the stringent European Commission (EC) regulations on emissions would entail unaffordable investments. For this very reason, the design of an innovative ultra-high bandwidth power-efficient network architecture is nowadays a bold topic within the research community. So far, the independent evolution of network layers has resulted in isolated, and hence, far-from-optimal contributions, which have eventually led to the issues today's networks are facing such as inefficient energy strategy, limited network scalability and flexibility, reduced network manageability and increased overall network and customer services costs. Consequently, there is currently large consensus among network operators and the research community that cross-layer interaction and coordination is fundamental for the proper architectural design of next-generation Internet networks. This thesis actively contributes to the this goal by addressing the modeling, optimization and performance analysis of a set of potential technologies to be deployed in future cross-layer network architectures. By applying a transversal design approach (i.e., joint consideration of several network layers), we aim for achieving the maximization of the integration of the different network layers involved in each specific problem. To this end, Part I provides a comprehensive evaluation of optical transport networks (OTNs) based on layer 2 (L2) sub-wavelength switching (SWS) technologies, also taking into consideration the impact of physical layer impairments (PLIs) (L0 phenomena). Indeed, the recent and relevant advances in optical technologies have dramatically increased the impact that PLIs have on the optical signal quality, particularly in the context of SWS networks. Then, in Part II of the thesis, we present a set of case studies where it is shown that the application of operations research (OR) methodologies in the desing/planning stage of future cross-layer Internet network architectures leads to the successful joint optimization of key network performance indicators (KPIs) such as cost (i.e., CAPEX/OPEX), resources usage and energy consumption. OR can definitely play an important role by allowing network designers/architects to obtain good near-optimal solutions to real-sized problems within practical running times

A Polyhedral Study of Mixed 0-1 Set

We consider a variant of the well-known single node fixed charge network flow set with constant capacities. This set arises from the relaxation of more general mixed integer sets such as lot-sizing problems with multiple suppliers. We provide a complete polyhedral characterization of the convex hull of the given set

p-Cycle Based Protection in WDM Mesh Networks

Abstract p-Cycle Based Protection in WDM Mesh Networks Honghui Li, Ph.D. Concordia University, 2012 WDM techniques enable single fiber to carry huge amount of data. However, optical WDM networks are prone to failures, and therefore survivability is a very important requirement in the design of optical networks. In the context of network survivability, p-cycle based schemes attracted extensive research interests as they well balance the recovery speed and the capacity efficiency. Towards the design of p-cycle based survivableWDM mesh networks, some issues still need to be addressed. The conventional p-cycle design models and solution methods suffers from scalability issues. Besides, most studies on the design of p-cycle based schemes only cope with single link failures without any concern about single node failures. Moreover, loop backs may exist in the recovery paths along p-cycles, which lead to unnecessary stretching of the recovery path lengths. This thesis investigates the scalable and efficient design of segment p-cycles against single link failures. The optimization models and their solutions rely on large-scale optimization techniques, namely, Column Generation (CG) modeling and solution, where segment pcycle candidates are dynamically generated during the optimization process. To ensure full node protection in the context of link p-cycles, we propose an efficient protection scheme, called node p-cycles, and develop a scalable optimization design model. It is shown that, depending on the network topology, node p-cycles sometimes outperform path p-cycles in iii terms of capacity efficiency. Also, an enhanced segment p-cycle scheme is proposed, entitled segment Np-cycles, for full link and node protection. Again, the CG-based optimization models are developed for the design of segment Np-cycles. Two objectives are considered, minimizing the spare capacity usage and minimizing the CAPEX cost. It is shown that segment Np-cycles can ensure full node protection with marginal extra cost in comparison with segment p-cycles for link protection. Segment Np-cycles provide faster recovery speed than path p-cycles although they are slightly more costly than path p-cycles. Furthermore, we propose the shortcut p-cycle scheme, i.e., p-cycles free of loop backs for full node and link protection, in addition to shortcuts in the protection paths. A CG-based optimization model for the design of shortcut p-cycles is formulated as well. It is shown that, for full node protection, shortcut p-cycles have advantages over path p-cycles with respect to capacity efficiency and recovery speed. We have studied a whole sequence of protection schemes from link p-cycles to path p-cycles, and concluded that the best compromise is the segment Np-cycle scheme for full node protection with respect to capacity efficiency and recovery time. Therefore, this thesis offers to network operators several interesting alternatives to path p-cycles in the design of survivable WDM mesh networks against any single link/node failures

Loss-free architectures in optical burst switched networks for a reliable and dynamic optical layer

For the last three decades, the optical fiber has been a quite systematic response to dimensioning issues in the Internet. Originally restricted to long haul networks, the optical network has gradually descended the network hierarchy to discard the bottlenecks. In the 90's, metropolitan networks became optical. Today, optical fibers are deployed in access networks and reach the users. In a near future, besides wireless access and local area networks, all networks in the network hierarchy may be made of fibers, in order to support current services (HDTV) and the emergence of new applications (3D-TV newly commercialized in USA). The deployment of such greedy applications will initiate an upward upgrade. The first step may be the Metropolitan Area Networks (MANs), not only because of the traffic growth, but also because of the variety of served applications, each with a specific traffic profile. The current optical layer is of mitigated efficiency, dealing with unforeseen events. The lack of reactivity is mainly due to the slow switching devices: any on-line decision of the optical layer is delayed by the configuration of the. devices. When the optical network has been extended in the MANs, a lot of efforts has been deployed to improve the reactivity of the optical layer. The Optical Circuit Switching paradigm (OCS) has been improved but it ultimately relies on off-line configuration of the optical devices. Optical Burst Switching (OBS) can be viewed as a highly flexible evolution of OCS, that operates five order of magnitude faster. Within this 'architecture, the loss-free guaranty can be abandoned in order to improve the reactivity of the optical layer. Indeed, reliability and reactivity appear as antagonists properties and getting closer to either of them mitigates the other. This thesis aims at proposing a solution to achieve reliable transmission over a dynamic optical layer. Focusing on OBS networks, our objective is to solve the contention issue without mitigating the reactivity. After the consideration of contention avoidance mechanisms with routing constraints similar as in OCS networks, we investigate the reactive solutions that intend to solve the contentions. None of the available contention resolution scheme can ensure the 100% efficiency that leads to loss-free transmission. An attractive solution is the recourse to electrical buffering, but it is notoriously disregarded because (1) it may highly impact the delays and (2) loss can occur due to buffer overflows. The efficiency of translucent architectures thus highly depends on the buffer availability, that can be improved by reducing the time spent in the buffers and the contention rate. We show that traffic grooming can highly reduce the emission delay, and consequently the buffer occupancy. In a first architecture, traffic grooming is enabled by a translucent core node architecture, capable to re-aggregate incoming bursts. The re-aggregation is mandatory to "de-groom" the bursts in the core network (i.e., to demultiplex the content of a burst). On the one hand, the re-aggregation highly reduces the loss probability, but on the other hand, it absorbs the benefits of traffic grooming. Finally, dynamic access to re-aggregation for contention resolution, despite the significant reduction of the contention rate, dramatically impacts the end-to-end delay and the memory requirement. We thus propose a second architecture, called CAROBS, that exploits traffic grooming in the optical domain. This framework is fully dynamic and can be used jointly with our translucent architecture that performs re-aggregation. As the (de)grooming operations do not involve re-aggregation, the translucent module can be restricted to contention resolution. As a result, the volume of data submitted to re-aggregation is drastically reduced and loss-free transmission can be reached with the same reactivity, end-to-end delay and memory requirement as a native OBS networ

RESILIENCE OF TRANSPORTATION INFRASTRUCTURE SYSTEMS: QUANTIFICATION AND OPTIMIZATION

Transportation systems are critical lifelines for society, but are at risk from natural or human-caused hazards. To prevent significant loss from disaster events caused by such hazards, the transportation system must be resilient, and thus able to cope with disaster impact. It is impractical to reinforce or harden these systems to all types of events. However, options that support quick recovery of these systems and increase the system's resilience to such events may be helpful. To address these challenges, this dissertation provides a general mathematical framework to protect transportation infrastructure systems in the presence of uncertain events with the potential to reduce system capacity/performance. A single, general decision-support optimization model is formulated as a multi-stage stochastic program. The program seeks an optimal sequence of decisions over time based upon the realization of random events in each time stage. This dissertation addresses three problems to demonstrate the application of the proposed mathematical model in different transportation environments with emphasis on system-level resilience: Airport Resilience Problem (ARP), Building Evacuation Design Problem (BEDP), and Travel Time Resilience in Roadways (TTR). These problems aim to measure system performance given the system's topological and operational characteristics and support operational decision-making, mitigation and preparedness planning, and post-event immediate response. Mathematical optimization techniques including, bi-level programming, nonlinear programming, stochastic programming and robust optimization, are employed in the formulation of each problem. Exact (or approximate) solution methodologies based on concepts of primal and dual decomposition (integer L-shaped decomposition, Generalized Benders decomposition, and progressive hedging), disjunctive optimization, scenario simulation, and piecewise linearization methods are presented. Numerical experiments were conducted on network representations of a United States rail-based intermodal container network, the LaGuardia Airport taxiway and runway pavement network, a single-story office building, and a small roadway network

Enabling Technology in Optical Fiber Communications: From Device, System to Networking

This book explores the enabling technology in optical fiber communications. It focuses on the state-of-the-art advances from fundamental theories, devices, and subsystems to networking applications as well as future perspectives of optical fiber communications. The topics cover include integrated photonics, fiber optics, fiber and free-space optical communications, and optical networking