PHYSICAL TOPOLOGY DESIGN AND ROUTING ALGORITHMS FOR DEGREE-CONSTRAINED FSO MESH NETWORKS

Free-space optical (FSO) mesh networks are emerging as broadband communication networks because of their high bandwidth (up to Gbps), low cost, and easy installation. However, there are two existing problems in the deployment of FSO networks: the physical topology design problem, and the routing problem. This dissertation presents an algorithm for the physical topology design of FSO mesh networks in order to enhance network reliability under defined degree constraint of each FSO node. The methodology presented enlarges the minimum angle between adjacent links at each node. Simulation results show that, compared to other methods, the proposed algorithm not only provides higher connectivity and lower delay for FSO networks, but also makes the FSO networks so constructed more tolerant in a dynamically changing environment. Further, this algorithm is enhanced to include the 3-dimensional (3-D) space, where the heights of the FSO nodes are not identical. This enhancement will apply to FSO nodes in difficult terrains where it is not feasible or desirable to have the FSO transceivers on a plane.This dissertation also addresses the routing problem in degree-constrained free-space optical (FSO) mesh networks. To solve the routing problem, four different routing algorithms are proposed. Their performances are evaluated through extensive simulations for a number of FSO mesh networks with different topologies and nodal degrees. The performance parameter against which these algorithms are evaluated is the mean end-to-end delay. The proposed least cost path (LCP) routing algorithm, which is based on minimizing the end-to-end delay, is considered as the bench mark. The performance of each of the other three algorithms is evaluated against the bench mark. The proposed minimum hop count with load-balancing (MHLB) routing algorithm is based on the number of hops between the source and the destination node to route the traffic. Simulation shows that the MHLB routing algorithm performs best in most cases compared with the other two. It results in minimum average delay and least blocked traffic

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