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Optical networks, employing Wavelength-Division Multiplexing (WDM) and wavelength routing, are believed to be the answer for the explosion in IP traffic and the emergence of real-time multimedia applications. These networks offer quantum leaps in transmission capacity as well as eliminate the electronic bottleneck in existing metropolitan and backbone networks. During the last decade, we witnessed a tremendous growth in the theoretical and experimental studies focusing on the cost-effective deployment of wavelength­ routed networks. The majority of these studies, however, assumed ideal behavior of optical devices. In this book, we argue that for the successful deployment of optical networks, design algorithms and network protocols must be extended to accommodate the non-ideal behavior of optical devices. These extensions should not only focus on maintaining acceptable signal quality (e.g., 12 maintaining BER above 10- ), but should also motivate the development of optimization algorithms and signaling protocols which take transmission impairments into consideration. In addition, the design of enabling technologies, such as optical cross-connects, should be transmission-efficient. This book is a comprehensive treatment of the impact of transmission impairments on the design and management of wavelength-routed networks. We start with transparent networks, focusing on power implications such as cross-connect design, device allocation problems, and management issues. In this all-optical model, we propose a design space based on reduction in overall cost and ease of network management. This design concept, motivates various switch architectures and different optimization problems.

Inhaltsverzeichnis

Frontmatter

Introduction

Chapter 1. Introduction

Abstract
The explosion in Internet traffic and the emergence of bandwidth-intensive delay-sensitive multimedia applications have a significant influence on the design of next generation telecommunication networks. These bandwidth-intensive delay-sensitive multimedia applications such as tele-medicine, virtual reality, data visualization, etc., are witnesses to a paradigm shift: the dawn of the multimedia age. The implication of these applications on telecommunication networks is powerful. Current telecommunication networks should evolve to match this paradigm shift. This means that they must move from being voice-centric and towards being data-centric. Photonic network technology is believed to be the answer. Photonic networking offers quantum leaps in both transmission capacity and node throughput by exploiting two major techniques: 1) Wavelength Division Multiplexing (WDM) and 2) Wavelength Routing. Wavelength division multiplexing offers the pre-eminent technology to take advantage of the enormous bandwidth of optical fibers [1]. WDM partitions the bandwidth of the fiber into many orthogonal channels where each channel is operated by an independent electronic device. An optical network consists of an interconnection of stations, cross-connects, and other devices using optical fiber.
Maher Ali

Transparent Networks

Frontmatter

Chapter 2. Power-Efficient Design of Multicast Networks

Abstract
In this chapter, we propose a power-efficient design space for multicast wavelength-routed networks. This design space is based on the impact of power on the overall design of wavelength-routed networks. Motivated by this design concept, we develop two new cross-connect architectures. The first architecture, Multicast-Only Splitter-and-Delivery (MOSaD), uses power splitters for multicast connections only, allowing unicast connections to pass without enduring unnecessary power losses. The second architecture, Tap-and-Continue (TaC), is based on tapping devices. Simulation results show that the MOSaD cross-connect offers substantial savings in the amount of amplification over existing cross-connect architectures with minimal effects on network performance. The power-efficient design space motivates several optimization problems, some of which are addressed in later chapters.
Maher Ali

Chapter 3. The Splitter Placement Problem: The Static Case

Abstract
We saw in the previous chapter that, realistically, only a subset of the cross-connects will be equipped with multicasting capabilities. Motivated by this observation, we introduce in this chapter the splitter placement in wavelength-routed networks (SP-WRN) problem. The SP-WRN problem is NP-complete as it includes as a subproblem the routing and wavelength assignment problem which is NP-complete. To gain a deeper insight into the computational complexity of the SP-WRN problem, we define a graph-theoretic version of the splitter placement problem (SPG), and show that even SPG is NP-complete. We develop three heuristics for the SP-WRN problem with different degrees of trade-off between computation time and quality of solution. The first heuristic uses the CPLEX general solver to solve an Integer-Linear Program (ILP) of the problem. The second heuristic is based on a greedy approach and is called Most-Saturated Node First (MSNF). The third heuristic employs Simulated Annealing (SA) with route-coordination. Through numerical examples on a wide variety of network topologies we demonstrate that: 1) no more than 50% of the cross-connects need to be multicast-capable, 2) the proposed SA heuristic provides fast near-optimal solutions, and 3) it is not practical to use general solvers such as CPLEX for solving the SP-WRN problem.
Maher Ali

Chapter 4. The Splitter Placement Problem: The Dynamic Case

Abstract
In the previous chapter, we investigated the static version of the splitter placement problem. The problem was addressed from a discrete point-of-view by considering the number of established sessions as the objective function. This chapter addresses the problem from a dynamic point-of-view where the traffic between network nodes is stochastic and thus the blocking probability is used as the objective function to minimize.
Maher Ali

Chapter 5. Routing and Wavelength Assignment with Power Considerations

Abstract
Routing and wavelength assignment (RWA) is an important problem that arises in wavelength-routed optical networks. Previous studies have solved many variations of this problem under the assumption of perfect conditions regarding the power of a signal. In this chapter, we investigate this problem while allowing for degradation of routed signals by components such as taps, multiplexers, switching elements, fiber links, etc. It is assumed that inline optical amplifiers are preplaced on individual fiber links at the physical design stage. We investigate the problem of routing the maximum number of connections while maintaining proper power levels. The problem is formulated as a mixed-integer nonlinear program. To overcome the complexity of the problem, we divide the problem into two parts. First, we solve the pure RWA problem using fixed routes for every connection. Second, power assignment is accomplished by either using the smallest-gain first (SGF) greedy heuristic or using a genetic algorithm. Numerical examples on a wide variety of networks show that: (a) the number of connections established without considering the signal attenuation is, for most of the time, greater than that achievable while considering the power, and (b) given adequate time, the genetic algorithm solution quality is much better than that of SGF, especially when the conflict graph of the connections generated by the linear solver is denser.
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Translucent Networks

Frontmatter

Chapter 6. Design of a Translucent Wide-Area Network

Abstract
In this chapter, we somewhat depart from the fully-transparent environment assumed so far. We acknowledge the fact that a fully transparent wide-area optical network is not feasible due to various signal impairments. The degradation in the signal quality dictates the need for signal regeneration at some strategic locations in the network. In this chapter, we introduce the design problem of dimensioning a given network to provide acceptable bit-error-rate (BER) for all connection demands with the objective of minimizing the cost of various optical and electronic components such as fiber links and regenerator nodes. The problem is non-trivial due to the interference between the optical channels when passing through the same optical amplifier (e.g., Erbium-Doped Fiber Amplifier EDFA). In addition, the aggregate power of all channels cannot exceed some threshold in order to prevent nonlinearity problems. We provide a mathematical formulation of the problem. Due to its difficulty, we propose an algorithmic solution approach. Numerical examples on different network topologies are presented which show the performance of our algorithms compared to obtained bounds when transmission impairment factors are relaxed.
Maher Ali

Chapter 7. Management of Polarization-Mode Dispersion

Abstract
In this chapter, we provide a detailed description of how the transmission impairments of the optical network can be accommodated for the dynamic provisioning of lightpaths. We show how one of the most important linear phenomena of optical transmission, Polarization-Mode Dispersion (PMD), is handled in the routing and management of translucent optical networks. A constraint-based routing algorithm and a label-distribution protocol are developed. Simulation results on the Italian network topology are provided to assess the regeneration requirements. We evaluate the impact of the transmission impairments on both the routing protocol as well as the overall cost of the network. Simulation results reveal that: 1) the feasibility of the lightpath is greatly affected by the PMD factor, especially for bit-rates exceeding 5Gb/s, and 2) significant improvement (in term of cost) can be achieved through intelligent route selection schemes which take into consideration physical characteristics of fiber links. These cost savings are more apparent in networks with non-homogeneous fiber quality.
Maher Ali

Chapter 8. Conclusions

Abstract
The optical networking area has witnessed rapid growth in recent years. Despite this rapid growth, there are still many questions to be answered. One main concern, is the influence that optical transmission impairments have on the optical network. In this book, we aimed at filling this gap by addressing the impact of transmission impairments on the overall design and management of wavelength-routed optical networks. The book was divided into two parts: Transparent and Translucent networks. In the transparent part, we provided four chapters. In Chapter 2, we focused on multicasting in wavelength-routed networks. We observed that current multicast-capable cross-connect architectures (e.g., Splitter-and-Delivery (SaD)) have two major problems: a) they require the use of a large number of optical power splitters; hence they are difficult and expensive to fabricate, and b) they have a high power budget requiring a large amount of amplification. We introduced the power-efficient design space that focuses on the reduction of both the number of splitters and the amount of amplification. One instance of that design concept is a cross-connect architecture called Multicast-Only Splitter and Delivery (MOSaD). The MOSaD architecture only utilizes W splitters, where W is the number of wavelengths supported. A second cross-connect architecture, Tap-and-Continue (TaC), was introduced. The TaC cross-connect utilizes only tapping devices and thus significantly reducing the amount of power loss.
Maher Ali

Backmatter

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