Browsing by Subject "Telecommunication networks"

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Open Access
An approach to manage connectionless services in connection-oriented networks
(IEEE, 1996) Abdelatı, Muhammed; Arıkan, Erdal
In this work we propose a pricing scheme which serves as an instrument for managing connectionless services in connection-oriented communication networks. The scheme is able to allocate network bandwidth in a Pareto-optimal way that maximizes the total surplus. The key idea is to decompose the service provision procedure among three separate parties whose interactions are governed by a set of competitive pricing mechanisms.
Open Access
Design of translucent optical networks: Partitioning and restoration
(Kluwer, 2004) Karasan, E.; Arisoylu, M.
We discuss the problem of designing translucent optical networks composed of restorable, transparent subnetworks interconnected via transponders. We develop an integer linear programming (ILP) formulation for partitioning an optical network topology into subnetworks, where the subnetworks are determined subject to the constraints that each subnetwork satisfies size limitations, and it is two-connected. A greedy heuristic partitioning algorithm is proposed for planar network topologies. We use section restoration for translucent networks where failed connections are rerouted within the subnetwork which contains the failed link. The network design problem of determining working and restoration capacities with section restoration is formulated as an ILP problem. Numerical results show that fiber costs with section restoration are close to those with path restoration for mesh topologies used in this study. It is also shown that the number of transponders with the translucent network architecture is substantially reduced compared to opaque networks.
Open Access
Dikgen frekans bölmeli çoklu erişim sistemlerinde telsiz erişim terminallerinin işbirliği
(IEEE, 2009-04) Tokel, Turgut Barış; Aktaş, Defne
Gelecek nesil kablosuz iletişim sistemlerinde öngörülen veri hızlarına ulaşabilmek için bu sistemlerde frekans yeniden kullanım oranının 1 olmasına ihtiyaç¸ vardır, bu ise özellikle hücre sınırlarındaki kullanıcıların önemli ölçüde hücreler arası girişime maruz kalmalarına neden olur. Telsiz erişim terminalleri arasında işbirliği hücreler arası girişimin azaltılmasında önemli bir rol oynamaktadır. Bu bildiride çok hücreli, çok girdili çok çıktılı, dikgen frekans bölmeli çoklu erişim sistemlerinde telsiz erişim terminallerinden kullanıcılara işbirlikli veri iletimi problemini ele alıyoruz. Telsiz erişim terminallerinin aralarında kısıtlı ileti paylaşımı ile çizelgeleme ve veri iletimi yaptıkları etkin bir işbirlikli algoritma öneriyoruz.
Open Access
An energy efficient scatternet formation algorithm for Bluetooth-based sensor networks
(IEEE, 2005-02) Saginbekov, Sain; Körpeoğlu, İbrahim
In this paper, we propose an energy-efficient scatternet formation algorithm for Bluetooth based sensor networks. The algorithm is based on first computing a shortest path tree from the base station to all sensor nodes and then solving the degree constraint problem so that the degree of each node in the network is not greater than seven, which is a Bluetooth constaint. In this way, less amount of energy is spent in each round of communication in the sensor network. The algorithm also tries to balance the load evenly on the high-energy consuming nodes which are the nodes that are close to the base station. In this way, the lifetime of the first dying node is also prolonged. We obtained promising results in the simulations. © 2005 IEEE.
Open Access
An ensemble classification model for detecting voice phishing in telecommunication networks and its integration into a visual analysis tool
(2022-09) Çalık, Hüseyin Eren
Voice phishing, a method of social engineering fraud performed over phone calls, has been a major problem globally since the use of phones became widespread. Traditional and modern methods to detect these fraud schemes include visual analysis of the customers’ behaviour, rule-based systems and machine learning models such as clustering, decision trees, shallow classifiers and deep learning models. Visual analysis depends only on human expertise and requires very high labor force to be effective. Rule-based systems are useful for extreme cases but are vulnerable to concept drifts. The-state-of-the-art methods generally utilize machine learning approaches. However, they require one or more of feature engineering done by experts, high computational power and privacy infringements. Therefore, in collaboration with Turkcell Technology, we aimed to develop a system that benefits from the advantages of the traditional methods while exploiting the effectiveness and efficiency of the state-of-the-art ones to tackle this issue. In doing so, we integrated an ensemble learning model to an existing visualization tool for detecting fraud users. This tool visualizes relational data as knowledge graphs, shows the informational data as texts and statistical data with charts and texts. Our ensemble learning model has two deep neural networks and one decision tree classifier. Multiple neural networks are used to reduce the variance and make a more stable model. One of them is composed of an input layer, two hidden layers with 200 nodes using Rectified Linear Unit (ReLU) activation function, each followed by a dropout layer and an output layer of one node with sigmoid activation function. We used dropout layers in this network to prevent over-fitting. The second neural network we built has 3 hidden layers instead with node numbers 64, 64 and 32, respectively, with ReLU as their activation function. To feed these models, a total of 34 features, 20 of which are raw, have been engineered with Turkcell fraud experts. The aggregation of the outputs is done by taking their average. We measured the success of our model by calculating the F1 Score as the class imbalance is high. Our model’s F1 score is 0.82 with a precision of 0.82 and a recall of 0.83. Also, with the integration of our model into this visualization tool, a framework was formed allowing mobile network operators to examine and detect fraud cases more efficiently and act accordingly.
Open Access
Foraging swarms as Nash equilibria of dynamic games
(IEEE, 2014) Özgüler, A. B.; Yildiz, A.
The question of whether foraging swarms can form as a result of a noncooperative game played by individuals is shown here to have an affirmative answer. A dynamic game played by N agents in 1-D motion is introduced and models, for instance, a foraging ant colony. Each agent controls its velocity to minimize its total work done in a finite time interval. The game is shown to have a unique Nash equilibrium under two different foraging location specifications, and both equilibria display many features of a foraging swarm behavior observed in biological swarms. Explicit expressions are derived for pairwise distances between individuals of the swarm, swarm size, and swarm center location during foraging.
Open Access
Free riding in peer-to-peer networks
(Institute of Electrical and Electronics Engineers, 2009) Karakaya, M.; Korpeoglu, I.; Ulusoy, Özgür
Free riding in peer-to-peer (P2P) networks poses a serious threat to their proper operation. Here, the authors present a variety of approaches developed to overcome this problem. They introduce several unique aspects of P2P networks and discuss free riding's effects on P2P services. They categorize proposed solutions and describe each category's important features and implementation issues together with some sample solutions. They also discuss open issues, including common attacks and security considerations. © 2009 IEEE.
Open Access
The latest arrival hub location problem
(Institute for Operations Research and the Management Sciences (INFORM), 2001) Kara, B. Y.; Tansel, B. Ç.
The traditionally studied hub location problems in the literature pay attention to flight times but not to transient times spent at hubs for unloading, loading, and sorting operations. The transient times may constitute a significant portion of the total delivery time for cargo delivery systems. We focus on the minimization of the arrival time of the last arrived item in cargo delivery systems and develop a model that correctly computes the arrival times by taking into account both the flight times and the transient times. Nonlinear and linear integer formulations are given and computational results are provided. The effects of delays on the system performance are analyzed.
Open Access
MPLS automatic bandwidth allocation via adaptive hysteresis
(Elsevier, 2010-11-29) Akar, N.; Toksöz, M. A.
MPLS automatic bandwidth allocation (or provisioning) refers to the process of dynamically updating the bandwidth allocation of a label switched path on the basis of actual aggregate traffic demand on this path. Since bandwidth updates require signaling, it is common to limit the rate of updates to reduce signaling costs. In this article, we propose a model-free asynchronous adaptive hysteresis algorithm for MPLS automatic bandwidth allocation under bandwidth update rate constraints. We validate the effectiveness of the proposed approach by comparing it against existing schemes in (i) voice and (ii) data traffic scenarios. The proposed method can also be used in more general GMPLS networks.
Open Access
New formulations for the hop-constrained minimum spanning tree problem via Sherali and Driscoll's tightened Miller-Tucker-Zemlin constraints
(Elsevier, 2010) Akgün, İbrahim
Given an undirected network with positive edge costs and a natural number p, the hop-constrained minimum spanning tree problem (HMST) is the problem of finding a spanning tree with minimum total cost such that each path starting from a specified root node has no more than p hops (edges). In this paper, the new models based on the Miller-Tucker-Zemlin (MTZ) subtour elimination constraints are developed and computational results together with comparisons against MTZ-based, flow-based, and hop-indexed formulations are reported. The first model is obtained by adapting the MTZ-based Asymmetric Traveling Salesman Problem formulation of Sherali and Driscoll [18] and the other two models are obtained by combining topology-enforcing and MTZ-related constraints offered by Akgün and Tansel (submitted for publication) [20] for HMST with the first model appropriately. Computational studies show that the best LP bounds of the MTZ-based models in the literature are improved by the proposed models. The best solution times of the MTZ-based models are not improved for optimally solved instances. However, the results for the harder, large-size instances imply that the proposed models are likely to produce better solution times. The proposed models do not dominate the flow-based and hop-indexed formulations with respect to LP bounds. However, good feasible solutions can be obtained in a reasonable amount of time for problems for which even the LP relaxations of the flow-based and hop-indexed formulations can be solved in about 2 days. © 2010 Elsevier Ltd. All rights reserved.
Open Access
OLSR-aware distributed channel access scheduling for wireless mesh networks
(IEEE, 2009-04) Kas, Miray; Körpeoğlu, İbrahim; Karasan, Ezhan
In this paper, we present OA-TDMA (OLSR-Aware TDMA), a TDMA based cross-layer channel access scheduling scheme which uses the information collected by the OLSR routing protocol. In OA-TDMA, each node makes decisions in a distributed manner with no central control, using the local information disseminated by the OLSR protocol. The distinctive feature of the OA-TDMA protocol lies in its weighting scheme where OA-TDMA approximates the traffic passing through each node by using the local topology information collected by OLSR. Our simulations on ns-2 confirm the significant performance improvement achieved by the combination of OLSR and OATDMA over other scheduling schemes considered in this paper. ©2009 IEEE.
Open Access
On the analysis of expected distance between sensor nodes and the base station in randomly deployed WSNs
(Springer Verlag, 2014) Sevgi, C.; Ali, S.A.
In this study, we focus on the analytical derivation of the expected distance between all sensor nodes and the base station (i.e., E[dtoBS]) in a randomly deployed WSN. Although similar derivations appear in the related literature, to the best of our knowledge, our derivation, which assumes a particular scenario, has not been formulated before. In this specific scenario, the sensing field is a square-shaped region and the base station is located at some arbitrary distance to one of the edges of the square. Having the knowledge of E[dtoBS] value is important because E[dtoBS] provides a network designer with the opportunity to make a decision on whether it is energy-efficient to perform clustering for WSN applications that aim to pursue the clustered architectures. Similarly, a network designer might make use of this expected value during the process of deciding on the modes of communications (i.e., multi-hop or direct communication) after comparing it with the maximum transmission ranges of devices. Last but not least, the use of our derivation is not limited to WSN domain. It can be also exploited in any domain when there is a need for a probabilistic approach to find the average distance between any given number of points which are all assumed to be randomly and uniformly located in any square-shaped region and at a specific point outside this region. © Springer International Publishing Switzerland 2014.
Open Access
On the design of AQM supporting TCP flows using robust control theory
(IEEE, 2004) Quet, P-F.; Özbay, Hitay
Recently it has been shown that the active queue management schemes implemented in the routers of communication networks supporting transmission control protocol (TCP) flows can be modeled as a feedback control system. Based on a delay differential equations model of TCPs congestion-avoidance mode different control schemes have been proposed. Here a robust controller is designed based on the known techniques for H∞ control of systems with time delays.
Open Access
On the design of AQM supporting TCP flows using robust control theory
(IEEE, 2003) Quet, P. F.; Özbay, Hitay
Recently it has been shown that the AQM (Active Queue Management) schemes implemented in the routers of communication networks supporting TCP (Transmission Control Protocol) flows can be modeled as a feedback control system. Based on a delay differential equations model of TCP's congestion-avoidance mode different control schemes have been proposed. Here a robust controller is designed based on the known techniques for ℋ ∞ control of systems with time delays.
Open Access
On the discrete adaptive posicast controller
(IFAC, 2015) Abidi, K.; Yıldız, Yıldıray
In this paper, we present the discrete version of the Adaptive Posicast Controller (APC) that deals with parametric uncertainties in systems with input time-delays. The continuous-time APC is based on the Smith Predictor and Finite Spectrum Assignment with time-varying parameters adjusted online. Although the continuous-time APC showed dramatic performance improvements in experimental studies with internal combustion engines, the full benefits could not be realized since the finite integral term in the control law had to be approximated in computer implementation. It is shown in the literature that integral approximation in time-delay compensating controllers degrades the performance if care is not taken. In this work, we present a development of the APC in the discrete-time domain, eliminating the need for approximation. In essence, this paper attempts to present a unified development of the discrete-time APC for systems that are linear with known/unknown input time-delays. Performances of the continuous-time and discrete-time APC, as well as conventional Model Reference Adaptive Controller (MRAC) for linear systems with known time-delay are compared in simulation studies. It is shown that discrete-time APC outperforms its continuoustime counterpart and MRAC. Further simulations studies are also presented to show the performance of the design for systems with uncertain time-delay.
Open Access
A path-quality-aware peer-to-peer file sharing protocol for mobile ad-hoc networks: Wi-Share
(IEEE, 2009-09) Karasabun, Efe; Ertemür, Doğuş; Sarıyıldız, Seyhun; Tekkalmaz, Metin; Körpeoğlu, İbrahim
Peer-to-peer networks are rather well-studied and currently there are numerous systems based on peer-to-peer principles running on the Internet. On the other hand peer-to-peer networks for mobile ad-hoc networks have attracted attention only in the recent years. In this paper, we propose a novel peer-to-peer file sharing system particularly designed for mobile ad-hoc networks. The proposed system, namely Wi-Share, has both network and application layer aspects enabling efficient search and download of the shared files. Wi-Share uses reactive routing for the search operation combined with source discovery and uses the routing tables constructed during the search operation for the download operation. In order to increase the overall efficiency of the file sharing in the network, Wi-Share applies techniques to reduce the required traffic and to increase efficient parallelism of the download operation. These techniques include filtering search results, preferring the higher quality routing paths, using partitioned download scheme and allowing the nodes that have joined to the network recently to contribute to the ongoing downloads. Wi-Share is implemented to work on mobile computers and the results of several experiments are also presented in the paper. © 2009 IEEE.
Open Access
A peer-to-peer file search and download protocol for wireless ad-hoc networks
(Elsevier BV, 2009-01) Sözer, H.; Tekkalmaz, M.; Korpeoglu, I.
Deployment of traditional peer-to-peer file sharing systems on a wireless ad-hoc network introduces several challenges. Information and workload distribution as well as routing are major problems for members of a wireless ad-hoc network, which are only aware of their immediate neighborhood. In this paper, we propose a file sharing system that is able to answer location queries, and also discover and maintain the routing information that is used to transfer files from a source peer to another peer. We present a cross-layer design, where the lookup and routing functionality are unified. The system works according to peer-to-peer principles, distributes the location information of the shared files among the members of the network. The paper includes a sample scenario to make the operations of the system clearer. The performance of the system is evaluated using simulation results and analysis is provided for comparing our approach with a flooding-based, unstructured approach. © 2008 Elsevier B.V. All rights reserved.
Open Access
Reducing query overhead through route learning in unstructured peer-to-peer network
(Academic Press, 2009-05) Çıracı, Salim; Körpeoǧlu, İ.; Ulusoy, Özgür
In unstructured peer-to-peer networks, such as Gnutella, peers propagate query messages towards the resource holders by flooding them through the network. This is, however, a costly operation since it consumes node and link resources excessively and often unnecessarily. There is no reason, for example, for a peer to receive a query message if the peer has no matching resource or is not on the path to a peer holding a matching resource. In this paper, we present a solution to this problem, which we call Route Learning, aiming to reduce query traffic in unstructured peer-to-peer networks. In Route Learning, peers try to identify the most likely neighbors through which replies can be obtained to submitted queries. In this way, a query is forwarded only to a subset of the neighbors of a peer, or it is dropped if no neighbor, likely to reply, is found. The scheme also has mechanisms to cope with variations in user submitted queries, like changes in the keywords. The scheme can also evaluate the route for a query for which it is not trained. We show through simulation results that when compared to a pure flooding based querying approach, our scheme reduces bandwidth overhead significantly without sacrificing user satisfaction. © 2008 Elsevier Ltd. All rights reserved.
Open Access
Regenerator location problem and survivable extensions: a hub covering location perspective
(Elsevier, 2015) Yıldız, B.; Karaşan, O. E.
In a telecommunications network the reach of an optical signal is the maximum distance it can traverse before its quality degrades. Regenerators are devices to extend the optical reach. The regenerator placement problem seeks to place the minimum number of regenerators in an optical network so as to facilitate the communication of a signal between any node pair. In this study, the Regenerator Location Problem is revisited from the hub location perspective directing our focus to applications arising in transportation settings. Two new dimensions involving the challenges of survivability are introduced to the problem. Under partial survivability, our designs hedge against failures in the regeneration equipment only, whereas under full survivability failures on any of the network nodes are accounted for by the utilization of extra regeneration equipment. All three variations of the problem are studied in a unifying framework involving the introduction of individual flow-based compact formulations as well as cut formulations and the implementation of branch and cut algorithms based on the cut formulations. Extensive computational experiments are conducted in order to evaluate the performance of the proposed solution methodologies and to gain insights from realistic instances.
Open Access
Regenerator placement and traffic engineering with restoration in GMPLS networks
(Springer, 2003) Yetginer, E.; Karasan, E.
In this paper, we study regenerator placement and traffic engineering of restorable paths in generalized multiprotocol label switching (GMPLS) networks. Regenerators are necessary in optical networks in order to cope with transmission impairments. We study a network architecture where regenerators are placed only at selected nodes for decreasing cost of regeneration. We propose two heuristic algorithms for optimum placement of these regenerators. Performances of these algorithms in terms of required number of regenerators and computational complexity are evaluated. In this network architecture with sparse regeneration, off-line computation of working and restoration paths is studied for traffic engineering with path rerouting as the restoration scheme. We study two approaches for selecting working and restoration paths from a set of candidate paths and formulate each method as an integer linear programming (ILP) problem. A traffic uncertainty model is developed in order to compare these methods based on their robustness with respect to changing traffic patterns. Traffic engineering methods are compared based on number of additional demands resulting from traffic uncertainties that can be carried over the network. Proposed heuristic regenerator placement algorithms are also evaluated from a traffic engineering point of view.