117 research outputs found
A Novel Solution to the Dynamic Routing and Wavelength Assignment Problem in Transparent Optical Networks
We present an evolutionary programming algorithm for solving the dynamic
routing and wavelength assignment (DRWA) problem in optical wavelength-division
multiplexing (WDM) networks under wavelength continuity constraint. We assume
an ideal physical channel and therefore neglect the blocking of connection
requests due to the physical impairments. The problem formulation includes
suitable constraints that enable the algorithm to balance the load among the
individuals and thus results in a lower blocking probability and lower mean
execution time than the existing bio-inspired algorithms available in the
literature for the DRWA problems. Three types of wavelength assignment
techniques, such as First fit, Random, and Round Robin wavelength assignment
techniques have been investigated here. The ability to guarantee both low
blocking probability without any wavelength converters and small delay makes
the improved algorithm very attractive for current optical switching networks.Comment: 12 Pages, IJCNC Journal 201
Combinatorial Optimization
This report summarizes the meeting on Combinatorial Optimization where new and promising developments in the field were discussed. Th
Approximation Algorithms for Survivable Multicommodity Flow Problems with Applications to Network Design
Multicommodity flow (MF) problems have a wide variety of applications in areas such as VLSI circuit design, network design, etc., and are therefore very well studied. The fractional MF problems are polynomial time solvable while integer versions are NP-complete. However, exact algorithms to solve the fractional MF problems have high computational complexity. Therefore approximation algorithms to solve the fractional MF problems have been explored in the literature to reduce their computational complexity. Using these approximation algorithms and the randomized rounding technique, polynomial time approximation algorithms have been explored in the literature. In the design of high-speed networks, such as optical wavelength division multiplexing (WDM) networks, providing survivability carries great significance. Survivability is the ability of the network to recover from failures. It further increases the complexity of network design and presents network designers with more formidable challenges. In this work we formulate the survivable versions of the MF problems. We build approximation algorithms for the survivable multicommodity flow (SMF) problems based on the framework of the approximation algorithms for the MF problems presented in [1] and [2]. We discuss applications of the SMF problems to solve survivable routing in capacitated networks
Network design problems in wavelength division multiplexing optical networks
Cataloged from PDF version of article.In this study, we analyze the network design problem arising in Wavelength
Division Multiplexing (WDM) networks where tra c is static, wavelength
interchanging is allowed and the location and number of the wavelength
interchangers are to be determined. Given a topology and tra c data, we try to
nd the ber and wavelength interchanger con guration with the minimum cost,
that can establish all given connections. We present di erent formulations of the
problem and some valid inequalities. Finally, we propose a heuristic method of
generating feasible solutions, apply the method on three di erent topologies with
varying tra c data, and present the results. The method is based on the idea of
partitioning the problem into two; routing problem and wavelength assignment
and interchanger location problem. Our results prove to be close to the lower
bounds we generate, and indicate that the ber cost performance of the case
where all nodes are wavelength interchangers can be attained using a relatively
small number of wavelength interchangers.Erdoğan, GüneşM.S
The Minimum Cost Design of Transparent Optical Networks Combining Grooming, Routing, and Wavelength Assignment
As client demands grow, optical network operators are required to introduce lightpaths of higher line rates in order to groom more demand into their network capacity. For a given fiber network and a given set of client demands, the minimum cost network design is the task of assigning routing paths and wavelengths for a minimum cost set of lightpaths able to groom all client demands. The variant of the optical network design problem addressed in this paper considers a transparent optical network, single hop grooming, client demands of a single interface type, and lightpaths of two line rates. We discuss two slightly different mixed integer linear programming models that define the network design problem combining grooming, routing, and wavelength assignment. Then, we propose a parameters increase rule and three types of additional constraints that, when applied to the previous models, make their linear relaxation solutions closer to the integer solutions. Finally, we use the resulting models to derive a hybrid heuristic method, which combines a relax-and-fix approach with an integer linear programming-based local search approach. We present the computational results showing that the proposed heuristic method is able to find solutions with cost values very close to the optimal ones for a real nation-wide network and considering a realistic fiber link capacity of 80 wavelengths. Moreover, when compared with other approaches used in the problem variants close to the one addressed here, our heuristic is shown to compute solutions, on average, with better cost values and/or in shorter runtimes
Resilient Resource Allocation Schemes in Optical Networks
Recent studies show that deliberate malicious attacks performed by high-power sig- nals can put large amount of data under risk. We investigate the problem of sur- vivable optical networks resource provisioning scheme against malicious attacks, more specically crosstalk jamming attacks. These types of attacks may cause ser- vice disruption (or possibly service denial). We consider optical networks based on wavelength-division multiplexing (WDM) technology and two types of jamming at- tacks: in-band and out-of-band attacks. We propose an attack-aware routing and wavelength assignments (RWA) scheme to avoid or reduce the damaging effects of potential attacking signals on individual or multiple legitimate lightpaths travers- ing the same optical switches and links. An integer linear programs (ILPs) as well as heuristic approaches were proposed to solve the problem. We consider dynamic traffic where each demand is dened by its start time and a duration. Our results show that the proposed approaches were able to limit the vulnerability of lightpaths to jamming attacks. Recently, large-scale failures caused by natural disasters and/or deliberate at- tacks have left major parts of the networks damaged or disconnected. We also investigate the problem of disaster-aware WDM network resource provisioning in case of disasters. We propose an ILP and efficient heuristic to route the lightpaths in such a way that provides protection against disasters and minimize the network vi resources such as the number of wavelength links used in the network. Our models show that signicant resource savings can be achieved while accommodating users demands. In the last few years, optical networks using Space Division Multiplexing (SDM) has been proposed as a solution to the speed bottleneck anticipated in data center (DC) networks. To our knowledge the new challenges of designing such communica- tion systems have not been addressed yet. We propose an optimal approach to the problem of developing a path-protection scheme to handle communication requests in DC networks using elastic optical networking and space division multiplexing. We have formulated our problem as an ILP. We have also proposed a heuristic that can handle problems of practical size. Our simulations explore important features of our approach
Bi-Criteria and Approximation Algorithms for Restricted Matchings
In this work we study approximation algorithms for the \textit{Bounded Color
Matching} problem (a.k.a. Restricted Matching problem) which is defined as
follows: given a graph in which each edge has a color and a profit
, we want to compute a maximum (cardinality or profit)
matching in which no more than edges of color are
present. This kind of problems, beside the theoretical interest on its own
right, emerges in multi-fiber optical networking systems, where we interpret
each unique wavelength that can travel through the fiber as a color class and
we would like to establish communication between pairs of systems. We study
approximation and bi-criteria algorithms for this problem which are based on
linear programming techniques and, in particular, on polyhedral
characterizations of the natural linear formulation of the problem. In our
setting, we allow violations of the bounds and we model our problem as a
bi-criteria problem: we have two objectives to optimize namely (a) to maximize
the profit (maximum matching) while (b) minimizing the violation of the color
bounds. We prove how we can "beat" the integrality gap of the natural linear
programming formulation of the problem by allowing only a slight violation of
the color bounds. In particular, our main result is \textit{constant}
approximation bounds for both criteria of the corresponding bi-criteria
optimization problem
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