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Keywords: min-max objective, translucent optical ring networks, traffic grooming.
The exponential growth of the Internet has resulted in an ever increasing demand for bandwidth. Carrier networks which form the backbone of the Internet, have been designed to carry only voice signals with predictable traffic patterns and anticipating slow growth of the network. With the advances in fiber optics and wavelength division multiplexing (WDM) optical networking is the key to satisfy the data-driven bandwidth demand. These technologies enable simultaneous transmission of signals on separate high-speed channels at different wavelengths. While the bandwidth provided by these channels is very high, individual traffic demands are at the sub-wavelength level. This mismatch can be overcome by multiplexing several lower rate connections onto the high-speed channels in a cost-effective manner. This technique is referred to as traffic grooming. Traffic grooming in WDM networks has been a widely addressed problem in recent years. Traffic grooming and its constituent subproblems have been proven to be NP-complete for even the most elemental of network topologies. The ring topology has been the target of a large number of the studies because of its practical relevance. However, most existing studies concentrate on some objective function that is aggregated over all the network nodes, such as the total number of ADMs used or the total amount of opto-electro-optical (OEO) routing performed. From a practical point of view, it is likely that every network node would be provisioned similarly. Hence a min-max objective, seeking to minimize the OEO equipment needed at the node which needs the maximum of such equipment is more appropriate. Such objectives are usually harder to optimize than aggregate objectives which are themselves known to be computationally intractable. In this thesis, we study traffic grooming in a unidirectional ring network under different traffic patterns for the min-max objective. We define two heuristic approaches based on decomposition; one is based.
This book presents the practical motivation, theoretical description, and extant techniques for traffic grooming in optical networks. The description of the various topics of research will be authored by leading researchers in this area, and will contain comprehensive description of related literature for each area. This book is intended to be a definitive reference and text for traffic grooming both for the practitioner in industry and the student in academia.
This book provides coverage of survivability and traffic grooming; two key issues in modern optical networks.
Optical networks based on wavelength-division multiplexing (WDM) tech nology offer the promise to satisfy the bandwidth requirements of the Inter net infrastructure, and provide a scalable solution to support the bandwidth needs of future applications in the local and wide areas. In a waveleng- routed network, an optical channel, referred to as a lightpath, is set up between two network nodes for communication. Using WDM technology, an optical fiber link can support multiple non-overlapping wavelength channels, each of which can be operated at the data rate of 10 Gbps or 40 Gbps today. On the other hand, only a fraction of customers are expected to have a need for such a high bandwidth. Due to the large cost of the optical backbone infrastruc ture and enormous WDM channel capacity, connection requests with diverse low-speed bandwidth requirements need to be efficiently groomed onto hi- capacity wavelength channels. This book investigates the optimized design, provisioning, and performance analysis of traffic-groomable WDM networks, and proposes and evaluates new WDM network architectures. Organization of the Book Significant amount of research effort has been devoted to traffic grooming in SONET/WDM ring networks since the current telecom networks are mainly deployed in the form of ring topologies or interconnected rings. As the long-haul backbone networks are evolving to irregular mesh topologies, traffic grooming in optical WDM mesh networks becomes an extremely important and practical research topic for both industry and academia.
We consider the problem of minimizing network costs when grooming traffic in optical networks that support Wavelength Division Multiplexing (WDM). While the general problem has been shown to be NP-Hard for a number of cost measures, there still exist restricted problems for which no complexity bound is known. In this research, we restrict our attention to traffic grooming for path networks with egress (all-to-one) traffic. This restricted model has practical significance for high speed (optical) access networks and can also lead to better bounds and approximations on more general network topologies (such as ring and star networks) that can be decomposed into path networks. Three important cost measures for this restricted model are studied. The first cost measure is the total number of ADMs used by the solution. Minimizing this cost was known to be NP-Complete even for egress traffic without using cross connects. We show that allowing an unbounded number of wavelengths obviates the need for digital cross connects at the nodes and hence the problem remains NP-Complete even when cross connects are allowed. The second cost measure is the number of transceivers used by the solution. We show that the problem of minimizing the number of transceivers is NP-Complete, even when restricted to egress traffic. We then develop a simple approximation scheme where the transceiver cost exceeds the minimum by at most the number of required wavelengths. Finally, we show that under certain conditions, there exist solutions that simultaneously minimize both ADM and transceiver costs. The third cost model aims to minimize the total electronic switching in the network. For this cost measure, we develop a polynomial time algorithm to determine the cost and structure of an optimum solution when the wavelength capacity constraint is relaxed. A closed form expression to determine the minimum cost is presented for problem instances with uniform traffic. We observe that these costs provide a l.
Wavelength Division Multiplexing (WDM) using wavelength routing has emerged as the dominant technology for use in wide area and metropolitan area networks. Traffic demands in networks today are characterized by dynamic, heterogeneous flows. While each wavelength has transmission capacity at gigabit per second rates, users require connections at rates that are lower than the full wavelength capacity. In this thesis, we explore network design and operation methodologies to improve the network utilization and blocking performance of wavelength routing networks which employ a layered architecture with electronic and optical switching. First we provide an introduction to first generation SONET/SDH networks and wavelength routing networks, which employ optical crossconnects. We explain the need and role of wavelength conversion in optical networks and present an algorithm to optimally place wavelength conversion devices at the network nodes so as to optimize blocking performance. Our algorithm offers significant savings in computation time when compared to the exhaustive method. To make the network viable and cost-effective, it must be able to offer sub-wavelength services and be able to pack these services efficiently onto wavelengths. The act of multiplexing, demultiplexing and switching of sub-wavelength services onto wavelengths is defined as traffic grooming. Constrained grooming networks perform grooming only at the network edge. Sparse grooming networks perform grooming at the network edge and the core. We study and compare the effect of traffic grooming on blocking performance in such networks through simulations and analyses. We also study the issue of capacity fairness in such networks and develop a connection admission control (CAC) algorithm to improve the fairness among connections with different capacities. We finally address the issues involved in dynamic routing and wavelength assignment in survivable WDM grooming networks. We develop two schemes for grooming primary and backup traffic steams onto wavelengths: Mixed Primary-Backup Grooming Policy (MGP) and Segregated Primary-Backup Grooming Policy (SGP). MGP is useful in topologies such as ring, characterized by low connectivity and high load correlation and SGP is useful in topologies, such as mesh-torus, with good connectivity and a significant amount of traffic switching and mixing at the nodes.