Browsing by Subject "Network analysis."

Now showing 1 - 6 of 6

Open Access
Comparative evaluation of spectrum allocation policies for dynamic flexgrid optical networks
(2013) Yümer, Ramazan
A novel class-based first-fit spectrum allocation policy is proposed for dynamic Flexgrid optical networks. The effectiveness of the proposed policy is compared against the first-fit policy for single-hop and multi-hop scenarios. Event-based simulation technique is used for testing the spectrum allocation policies under both Fixed Routing and Fixed Alternate Routing algorithms with two shortest paths. Throughput is shown to be consistently improved under the proposed policy with gains of up to 15 % in certain scenarios.
Open Access
Hub & regenerator location and survivable network design
(2010) Özkök, Onur
With the vast development of the Internet, telecommunication networks are employed in numerous different outlets. In addition to voice transmission, which is a traditional utilization, telecommunication networks are now used for transmission of different types of data. As the amount of data transmitted through the network increases, issues such as the survivability and the capacity of the network become more imperative. In this dissertation, we deal with both design and routing problems in telecommunications networks. Our first problem is a two level survivable network design problem. The topmost layer of this network consists of a backbone component where the access equipments that enable the communication of the local access networks are interconnected. The second layer connects the users on the local access network to the access equipments, and consequently to the backbone network. To achieve a survivable network, one that stays operational even under minor breakdowns, the backbone network is assumed to be 2-edge connected while local access networks are to have the star connectivity. Within the literature, such a network is referred to as a 2-edge connected/star network. Since the survivability requirements of networks may change based on the purposes they are utilized for, a variation of this problem in which local access networks are also required to be survivable is also analyzed. The survivability of the local access networks is ensured by providing two connections for every component of the local access networks to the backbone network. This architecture is known as dual homing in the literature. In this dissertation, the polyhedral analysis of the two versions of the two level survivable network design problem is presented; separation problems are analyzed; and branch-and-cut algorithms are developed to find exact solutions. The increased traffic on the telecommunications networks requires the use of high capacity components. Optical networks, composed of fiber optical cables, offer solutions with their higher bandwidths and higher transmission speeds. This makes the optical networks a good alternative to handle the rapid increase in the data traffic. However, due to signal degradation which makes signal regeneration necessary introduces the regenerator placement problem as signal regeneration is a costly process in optical networks. In the regenerator placement problem, we study a location and routing problem together on the backbone component of a given telecommunications network. Survivability is also considered in this problem simultaneously. Exact solution methodologies are developed for this problem: mathematical models and some valid inequalities are proposed; separation problems for the valid inequalities are analyzed and a branch-and-cut algorithm is devised.
Open Access
Regenerator placement in optical networks
(2004) Özkök, Onur
Increase in the number of users and resources consumed by modern applications results in an explosive growth in the traffic on the Internet. Optical networks with higher bandwidths offer faster and more reliable transmission of data and allows transmission of more data. Fiber optical cables have these advantages over the traditional copper wires. So it is expected that optical networks will have a wide application area. However, there are some physical impairments and optical layer constraints in optical networks. One of these is signal degradation which limits the range of optical signals. Signals are degraded during transmission and below a threshold the signals become useless. In order to prevent this, regenerators which are capable of re-amplifying optical signals are used. Since regeneration is a costly process, it is important to decrease the number of regenerators used in an optical network. To increase the reliability of the network, two edge-disjoint paths between each terminal on the network are to be constructed. So the second path could be used in case of a failure in transmitting data on an edge of the first path. Considering these requirements, selecting the nodes on which regenerators are to be placed is an important decision. In this thesis, we discuss the problem of placing signal regenerators on optical networks with restoration. An integer linear program is formulated for this problem. Due to the huge size and other problems of the formulation, it is impractical to use it on large networks. For this reason, a fast heuristic algorithm is proposed to solve this problem. Three methods are proposed to check the feasibility when a fixed set of regenerators are placed on specific nodes. Additionally, a branch and bound algorithm which employs the proposed heuristic is developed to find the optimal solution of our problem. Performance of both the heuristics and the branch and bound method are evaluated in terms of number of regenerators placed and solution times of the algorithms.
Open Access
A review of network location theory and models
(2004) Erdoğan, Damla Selin
In this study, we review the existing literature on network location problems. The study has a broad scope that includes problems featuring desirable and undesirable facilities, point facilities and extensive facilities, monopolistic and competitive markets, and single or multiple objectives. Deterministic and stochastic models as well as robust models are covered. Demand data aggregation is also discussed. More than 500 papers in this area are reviewed and critical issues, research directions, and problem extensions are emphasized.
Open Access
Routing, spectrum allocation and regenerator placement in flexible-grid optical networks
(2013) Kahya, Alper
Tremendous increase in the number of wireless devices has been resulting in huge growth in the Internet traffic. This growth necessitates efficient usage of resources in the optical networks, which form the backbone of the Internet. Recently proposed flexible optical networks can adjust the optical layer transmission parameters to take advantage of existing channel conditions thereby increasing the resource utilization efficiency. Therefore, flexible optical network is a promising solution to fulfill growing future demand of IP traffic. Apart from efficient usage of the optical spectrum, the degradation of the optical signal as it propagates over the fiber is another problem. In such cases, the optical signal must be regenerated when a lightpath travels longer than the maximum optical reach. However, regenerators are expensive devices with high operational costs. Therefore, they should be placed carefully to reduce the capital and operational network costs. In this dissertation, we deal with the joint routing, spectrum allocation and regenerator placement (RSA-RP) problem for flexible optical networks. Our aim is to find the route and allocate spectrum for each traffic demand by assigning minimum number of nodes as regenerator sites. Firstly, we introduce a novel mixed integer linear programming (MILP) formulation for the joint RSA-RP problem. Since this formulation is not practical for large networks, we propose a decoupled formulation where the RSA-RP problem is decomposed into two phases. In the first step, we find routes and locations of regenerators assuming a full wavelength converting network. Then, we allocate the spectrum to each demand in the second phase. The decoupled model can be used to solve the RSA-RP problem for reasonably sized optical networks. We show that the decoupled model can find optimum solutions for 92% of the all cases tested for the NSFNET topology and 99% of the all cases tested for the Deutsche Telecom topology. We also show that the locations of regenerator sites significantly depend on network parameters such as the node degree and lengths of the links adjacent to the node.
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.