Browsing by Subject "Tabu Search"

Now showing 1 - 5 of 5

Open Access
Algorithms for the integer multicommodity network design problem
(2004) Kılınç, Mustafa Rasim
In this thesis, we study the problem of logical network design in telecommunication networks. Given a set of nodes and a set of commodities, we aim to locate lightpaths(links) between nodes and route the commodities over these lightpaths. The cost to be minimized is the number of lightpaths used. The problem has capacity, degree and delay constraints. An important characteristic of our problem is that the commodities can not be split, therefore they must be routed on a single path. We present two integer programming formulations of the problem and consider four sets of valid inequalities. Additionally, a relaxation of the problem is presented to obtain a lower bound to the problem. Finally, we propose two algorithms of generating good feasible solutions to the problem. Our results prove to be close to the lower bounds.
Open Access
Regenerator placement in elastic optical networks with adaptive modulation and coding
(2016-09) Gamgam, Onur Berkay
Due to the rapid and diverse increase in the tra c load on the optical networks, e cient utilization of the network resources becomes an important issue. Using di erent modulation formats and coding rates in optical signal transmission, it is possible to assign di erent spectral e ciency and optical reach for each tra c requests. To satisfy the quality of transmission (QoT) for the distances beyond optical reach, optical - electronic - optical (O/E/O) 3R regeneration of the optical signal is required. During the regeneration process, the spectral e ciency and thus optical reach of the resultant signal can also be set. In these circumstances, by selecting speci c regenerator node locations and assigning di erent line rates for each tra c request, the network utilization can be optimized. Joint selection of regenerator placement (RP), routing and adaptive modulation and coding (AMC) pro le in elastic optical networks (EON) is studied to propose an o ine RP algorithm for a given network topology with link length and link capacity constraints. For a given RP, an Integer Linear Programming (ILP) model is formulated to perform routing and AMC pro le assignment for each tra c demand. We use two di erent approaches for determining candidate paths for routing: In the rst set, k shortest paths (KSP) are utilized for all cases. In the second set, namely regenerator location dependent path selection (RLDPS), the candidate paths are determined according to the given RP. To nd the minimum cost RP among all possibilities, Tabu Search based regenerator placement algorithm (TSRPA) is proposed. Results show that adaptively selecting the candidate paths based on the regenerator locations reduces network utilization either by decreasing the number of regenerator nodes by up to 66.6% or decreasing link capacity utilization by up to 5.09% as compared to selecting candidate paths as xed k shortest paths. The regenerator node location distribution obtained with RLDPS concentrated on smaller number of nodes compared to the results obtained with KSP. By placing regenerators at a signi cantly less number of nodes, capital expenditures (CAPEX) are reduced by RLDPS.
Open Access
A tabu search algorithm for sparse placement of wavelength converting nodes in optical networks
(2004) Şengezer, Namık
All-optical Wavelength Division Multiplexing networks, providing extremely large bandwidths, are among the most promising solutions for the increasing need for high-speed data transport. In all-optical networks, data is transmitted solely in the optical domain along lightpaths from source to destination without being converted into the electronic form, and each lightpath is restricted to use the same wavelength on all the links along its path. This restriction is known as the wavelength continuity constraint. Optical wavelength conversion can increase the performance and capacity of optical networks by removing this restriction and relaxing the wavelength continuity constraint. However, optical wavelength conversion is a difficult and expensive technology. In this study, we analyze the problem of placing limited number of wavelength converting nodes in a multi- fiber network with static traffic demands. Optimum placement of wavelength converting nodes is an NP-complete problem. We propose a tabu search based heuristic algorithm for this problem. The objective of the algorithm is to achieve the performance of full wavelength conversion in terms of minimizing the total number of fibers used in the network by placing minimum number of wavelength converting nodes. Numerical results comparing the performance of the algorithm with the optimum solutions are presented. The proposed algorithm gives quite satisfactory results, it also has a relatively low computational complexity making it applicable to large scale networks.
Open Access
Tabu search with fully sequential procedure for simulation optimization
(2003) Çevik, Savaş
Simulation is a descriptive technique that is used to understand the behaviour of both conceptual and real systems. Most of the real life systems are dynamic and stochastic that it may be very difficult to derive analytical representation. Simulation can be used to model and to analyze these systems. Although simulation provides insightful information about the system behaviour, it cannot be used to optimize the system performance. With the development of the metaheuristics, the concept simulation optimization has became a reality in recent years. A simulation optimization technique uses simulation as an evaluator, and tries to optimize the systems performance by setting appropriate values of simulation input. On the other hand, statistical ranking and selection procedures are used to find the best system design among a set of alternatives with a desired confidence level. In this study, we combine these two methodologies and investigate the performance of the hybrid procedure. Tabu Search (TS) heuristic is combined with the Fully Sequential Procedure (FSP) in simulation optimization context. The performance of the combined procedure is examined in four different systems. The effectiveness of the FSP is assessed considering the computational effort and the convergence to the best (near optimal) solution.
Open Access
Topology design in communication networks
(2003) Kepek, İlktuğ Çağatay
In this thesis, we study the topology design problem in communication networks. It is the problem of a Virtual Private Network(VPN) provider. Given a set of customer nodes and a set of commodities, we aim to locate links between customer nodes and route the commodities over these links. The cost to be minimized is the sum of location and routing costs. The problem has capacity, degree and delay constraints. An important characteristic of the problem is that the commodities cannot be split, therefore they must be routed over single paths. We present an integer programming formulation of the problem and introduce two sets of valid inequalities. The problem has two parts: locating links and routing commodities. We first analyze the commodity routing problem and propose an efficient heurisric for it. Finally we propose a heuristic method of generating good feasible solutions to our problem. The final heuristic is a Tabu Search which uses the first heuristic proposed for routing problem as a subroutine. Our results prove to be closer to the lower bounds we generate than previously proposed heuristics.