Browsing by Subject "Network analysis (Planning)."

Now showing 1 - 9 of 9

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
Distance constraints on cyclic networks : a new polynomially solvable class
(1997) Emir, Hülya
Distance Constraints Problem is to locate new facilities on a network so that the distances between new and existing facilities as well as between pairs of now facilities do not exceed given upper bounds, 'rhc ])roblem is N F-Complele on cyclic networks. The oidy known polynornially solvable class of distance constraints on cyclic networks is the case when the linkage network, which is an auxiliary graph induced by the distance bounds between new facility pairs, is a tree. In this thesis, we identify a new polynornially solvable class where each new facilit}'^ is restricted to an a priori specified feasible region which is confined to a single edge and where the linkage network is cj^clic with the restriction that there exists a node whose deletion breaks all cycles. We then extend the above class to a more general class where the linkage network has a cut vertex whose blocks fulfill the above assumptions
Open Access
Joint topology design with routing and power control in ad hoc networks
(2003) Önal, Aydoğan
We discuss the problem of designing an ad hoc network topology by jointly using power control and routing. A well-designed topology in ad hoc networks provides several advantages: increasing the capacity, decreasing the complexity and reducing the power consumption. We formulate the topology design problem as an Integer Linear Programming (ILP) model. An optimal topology is designed subject to interference and connectivity constraints with three different objective functions and two power control approaches. Common transmit power (COMPOW) and the adaptive power (ADPOW) are the two different power control techniques used in this thesis. The objectives of the models that are used in the topology design are maximizing the number of established links, using shortest path routing strategy and minimizing the maximum traffic load over the most congested link by load balancing. Performance comparisons between two power control approaches with three different objectives in the topology design are achieved using numerical results on a sample network. Minimum end-to-end throughput, total throughput, total power consumption and the number of established links are used as the performance metrics. The numerical results show that selecting the optimal power for both power control approaches provides similar performance results. Therefore, simplicity of the COMPOW makes it more attractive than ADPOW in the topology design.
Open Access
Planar p-center problem with Tchebychev distance
(1994) Yılmaz, Dilek
The p-center problem is a model for locating p facilities to serve clients so that the distance between a farthest client and its closest facility is minimized. Emergency service facilities such as fire stations, hospitals and police stations are most of the time located in this manner. In this thesis, the planar p-center problem with Tchebychev distance is studied. The problem is known to be NPHard. We identify certain polynomial time solvable cases and give an efficient branching method which makes use of polynomial time methods in subproblem solutions whenever possible. In addition, a dual problem is posed in light of the existing duality theory on tree networks.
Open Access
Polynomially solvable cases of multifacility distance constraints on cyclic networks
(1993) Yeşilkökçen, Naile Gülcan
Distance Constraints Problem is to locate one or more new facilities on a network so that the distances between new and existing facilities as well as between pairs of new facilities do not exceed given upper bounds. The problem is AfV-Complete on cyclic networks and polynomially solvable on trees. Although theory for tree networks is well-developed, there is virtually no theory for cyclic networks. In this thesis, we identify a special class of instances for which we develop theory and algorithms that are applicable to any metric space defining the location space. We require that the interaction between new facilities has a tree structure. The method is based on successive applications of EXPANSION and INTERSECTION operations defined on subsets of the location space. Application of this method to general networks yields strongly polynomial algorithms. Finally, we give an algorithm that constructs an e-optimal solution to a related minimax problem.
Open Access
Sensitivity analysis of distance constraints and of multifacility minimax location on tree networks
(1989) Doğan, Esra
In this thesis, the main concern is to investigate the use of consistency conditions of distance constraints in sensitivity analysis of certain network location problems. The interest is in minimax type of objective functions. A single parametric approach is adopted in the sensitivity analysis for the m-facility minimax location problem on tree networks. Apart from the traditional sensitivity analysis approach, a conceptual framework for imprecision in distance constraints is developed.
Open Access
A spanning tree approach to solving the absolute p-center problem
(1995) Bozkaya, Burçin
The p-center problem on a network is a model to locate p new facilities that will serve n existing demand points on that network. The objective is to minimize the maximum of the weighted distances between each demand point and its nearest new facility. This type of problem usually arises in the location of emergency facilities like hospitals, police and fire stations. The problem is known to be VP-Hard on a cyclic network, but polynomial-time solvable on a tree network. In this study, a spanning tree approach to solving the problem on a cyclic network is discussed. First, the existence of an optimal spanning tree that gives the network optimal solution, is proved. Then, two specific types of spanning trees are introduced and experimentally tested whether they contain the optimal tree or not. Also, some properties of such an optimal tree are discussed and some special cases for which the optimal tree can be determined in polynomial time, are identified.
Open Access
Topology design and scheduling in STDMA based wireless ad hoc networks
(2003) Ergin, Sadettin Alp
With current advances in technology, wireless networks are increasing in popularity. Wireless networks allow users the freedom to travel from one location to another without interruption of their communication activities. Ad hoc networks, a subset of wireless networks, allow the formation of a wireless network without the need for a base station. Since no fixed infrastructure is involved in the communication, the nodes of ad hoc networks can communicate with each other or can relay data to other nodes. With this flexibility, wireless ad hoc networks have the ability to form a network anywhere, at any time, as long as two or more wireless users are willing to communicate. Managing ad hoc networks is a significantly more difficult task than managing wireline networks. The network requirements should be met by combined efforts of all the mobile nodes themselves. The nodes of ad hoc networks often operate under severe constraints, such as limited battery power, variable link quality and limited shared bandwidth. In this study, the topology design issue in ad hoc wireless networks is investigated. We employ hierarchical routing where the network topology is composed of clusters interconnected via a root node. Cluster-based topologies are suitable for military services, an important application area for ad hoc networks. The common power control technique (COMPOW) is used in this thesis where all nodes transmit at the same power level. Nodes employ the spatial TDMA (STDMA) scheme in order to access the channel. An important task is how to produce a minimum STDMA frame length, and this problem is known to be NP complete. We develop a heuristic algorithm for generating the minimum STDMA frame length. A new interference model for ad hoc networks is proposed which utilizes a hypergraph model. The relationship between the frame length, number of clusters and the transmit power level are investigated through numerical examples using a 15- node network.
Open Access
Wavelength assignment in optical burst switching networks using neuro-dynamic programming
(2003) Keçeli, Feyza
All-optical networks are the most promising architecture for building large-size, hugebandwidth transport networks that are required for carrying the exponentially increasing Internet traffic. Among the existing switching paradigms in the literature, the optical burst switching is intended to leverage the attractive properties of optical communications, and at the same time, take into account its limitations. One of the major problems in optical burst switching is high blocking probability that results from one-way reservation protocol used. In this thesis, this problem is solved in wavelength domain by using smart wavelength assignment algorithms. Two heuristic wavelength assignment algorithms prioritizing available wavelengths according to reservation tables at the network nodes are proposed. The major contribution of the thesis is the formulation of the wavelength assignment problem as a continuous-time, average cost dynamic programming problem and its solution based on neuro-dynamic programming. Experiments are done over various traffic loads, burst lengths, and number of wavelength converters with a pool structure. The simulation results show that the wavelength assignment algorithms proposed for optical burst switching networks in the thesis perform better than the wavelength assignment algorithms in the literature that are developed for circuit-switched optical networks.