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Item Open Access An algorithm for energy-efficient bluetooth scatternet formation and maintenance(IEEE, 2004-09) Pamuk, Canan; Karasan, EzhanShow more We discuss an energy-efficient, distributed Bluetooth Scatternet Formation algorithm based on Device and Link characteristics (SF-DeviL). SF-DeviL forms multihop scatternets with tree topologies and increases battery lif etimes of devices by using device types, battery levels and received signal strengths. The topology is dynamically reconfigured in SF-DeviL by depleting battery levels and it is shown through simulations that the network lifetime is increased by at least 32% compared to LMS algorithm [1].Show more Item Open Access Bluetooth or 802.15.4 technologies to optimise lifetime of wireless sensor networks: Numerical comparison under a common framework(IEEE, 2008-04) Buratti, C.; Körpeoğlu, İbrahim; Karasan, Ezhan; Verdone, R.Show more This paper aims at comparing through simulations the network lifetime of a wireless sensor network using Bluetooth-enabled or IEEE802.15.4 compliant devices. The evaluation is performed under a common reference framework, namely the EMORANS scenario for wireless sensor networks. Since the two enabling technologies rely on different MAC paradigms, suitable definition of the performance metrics is needed, in order to make the comparison meaningful. Thus, the paper has also a methodological objective. In particular, three different definitions of network lifetime are introduced, and a comparison of performance obtained by applying the different definitions is provided. Then, the comparison between the two standards is introduced: it is shown that there are no orders of magnitude of difference in network lifetime when the two technologies are used and the choice of the technology depends on the application requirements.Show more Item Open Access A comparative study of single-layer and multi-layer traffic engineering approaches on transparent optical networks(IEEE, 2007) Şengezer, Namık; Puype, B.; Karasan, Ezhan; Pickavet, M.Show more This paper comparatively studies single-layer and multi-layer traffic engineering strategies on an IP/MPLS/WDM network. These strategies are evaluated and compared in two different scenarios. In the first scenario, the strategies make use of statistical information on the traffic patterns. In the second scenario, the traffic engineering decisions are based on the instantaneous traffic information only. The performance and benefits of both approaches are discussed based on simulations considering both throughput and network resource usage. © 2007 IEEE.Show more Item Open Access Effect of number of burst assemblers on TCP performance in optical burst switching networks(IEEE, 2006-10) Gürel, Güray; Karasan, EzhanShow more Burst assembly mechanism is one of the fundamental factors that determine the performance of an optical burst switching (OBS) network. In this paper, we investigate the influence of number of burstifiers on TCP performance for an OBS network. An ns2-based OBS network simulator is developed for simulating the optical network. The goodput of TCP flows between an ingress and an egress nodes traveling through an optical network is studied for different values of the number of assembly buffers per destination. First, the losses resulting from the congestion in the core OBS network are modeled using a burst independent Bernoulli loss model. Then, a background burst traffic is generated to create contention at a core node in order to realize a burst dependent loss model. Simulation results show that for an OBS network employing timer-based assembly algorithm, TCP goodput increases as the number of burst assemblers is increased for both types of loss models. The improvement from one burstifier to moderate number of burst assemblers is significant (15-50% depending on the burst loss probability, processing delay and the TCP version), but the goodput difference between moderate number of buffers andperflow aggregation is relatively small, implying that a cost-effective OBS edge switch implementation should use moderate number of assembly buffers per destination for enhanced TCP performance. © 2006 IEEE.Show more Item Open Access The effect of terrain roughness in the microwave line-of-sight multipath fading estimation based on Rec. ITU-R P.530-15(IEEE, 2014-08) Göktas, Polat; Altıntaş, Ayhan; Topçu, Satılmış; Karasan, Ezhan; Göktas, Polat; Altıntaş, Ayhan; Topçu, Satılmış; Karasan, EzhanShow more Multipath fading is an important constraint on the prediction of path loss for terrestrial line-of-sight microwave links. The International Telecommunication Union - Radiocommunication (ITU-R) Rec. P.530 [1] is one of the most widely used methods providing guidelines for the design of terrestrial line-of-sight links. The purpose of the study presented in this paper is to make an investigation of the effect of both terrain roughness and geoclimatic factor parameters in the path loss characteristics of microwave line-of-sight (LOS) propagation in NATO Band 3+ (1350-2690 MHz) and NATO Band 4 (4440-5000 MHz) frequency ranges. The two parameters led to significantly different results for the link availability due to multipath fading as a function of the fade margin. © 2014 IEEE.Show more Item Open Access An efficient virtual topology design and traffic engineering scheme for IP/WDM networks(Springer, 2007) Şengezer, Namık; Karasan, EzhanShow more We propose an online traffic engineering (TE) scheme for efficient routing of bandwidth guaranteed connections on a Multiprotocol label switching (MPLS)/wavelength division multiplexing (WDM) network with a traffic pattern varying with the time of day. We first consider the problem of designing the WDM virtual topology utilizing multi-hour statistical traffic pattern. After presenting an effective solution to this offline problem, we introduce a Dynamic tRaffic Engineering AlgorithM (DREAM) that makes use of the bandwidth update and rerouting of the label switched paths (LSPs). The performance of DREAM is compared with commonly used online TE schemes and it is shown to be superior in terms of blocked traffic ratio.Show more Item Open Access Exact calculation of blocking probabilities for bufferless optical burst switched links with partial wavelength conversion(IEEE, 2004-10) Akar, Nail; Karasan, EzhanShow more In this paper, we study the blocking probabilities in a wavelength division multiplexing-based asynchronous bufferless optical burst switch equipped with a bank of tuneable wavelength converters that is shared per output link. The size of this bank is generally chosen to be less than the number of wavelengths on the link because of the relatively high cost of wavelength converters using current technologies; this case is referred to as partial wavelength conversion in the literature. We present a probabilistic framework for exactly calculating the blocking probabilities. Burst durations are assumed to be exponentially distributed. Burst arrivals are first assumed to be Poisson and later generalized to the more general phase-type distribution. Unlike existing literature based on approximations and/or simulations, we formulate the problem as one of finding the steadystate solution of a continuous-time Markov chain with a block tridiagonal infinitesimal generator. We propose a numerically efficient and stable solution technique based on block tridiagonal LU factorizations. We show that blocking probabilities can exactly and efficiently be found even for very large systems and rare blocking probabilities. Based on the results of this solution technique, we also show how this analysis can be used for provisioning wavelength channels and converters. © 2004 IEEE.Show more Item Open Access Multipath fading effect on terrestrial microwave LOS radio links(IEEE, 2015-07) Göktaş Polat; Topçu, Satılmış; Karasan, Ezhan; Altıntaş, Ayhan; Göktaş Polat; Topçu, Satılmış; Karasan, Ezhan; Altıntaş, AyhanShow more In this paper, the calculation of both the total received power with the effect of the ground reflection and the fade margin to find out the link availability for terrestrial microwave LOS (line-of-sight) radio links is proposed. The expressions are derived from clear-air, rainfall propagation mechanisms and multipath fading due to multipath arising from surface reflection along the defined microwave LOS radio link. We verify the mathematical model by using the ATDI ICS telecom software over sample microwave LOS radio links located in Turkey. © 2015 IEEE.Show more Item Open Access A new approach to diffraction modelling for line-of-sight (LOS) paths(IEEE, 2015) Topçu, Satılmış; Göktaş, Polat; Karasan, Ezhan; Altıntaş, Ayhan; Topçu, Satılmış; Göktaş, Polat; Karasan, Ezhan; Altıntaş, AyhanShow more In this paper, we present a new knife-edge diffraction method based on Bullington method for the terrestrial line-of-sight (LOS) paths. The diffraction loss of our new knife-edge diffraction method is compared with the results obtained from the Delta-Bullington method and the measurement data existing in the literature for sample fixed terrestrial microwave line-of-sight (LOS)/ non line-of-sight (NLOS) radio links. The revised Bullington method is shown to perform significantly better than the Delta-Bullington method for both overland and coastal/overwater radio links.Show more Item Open Access OLSR-aware distributed channel access scheduling for wireless mesh networks(IEEE, 2009-04) Kas, Miray; Körpeoğlu, İbrahim; Karasan, EzhanShow more 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.Show more Item Open Access Packet loss analysis of synchronous buffer-less optical switch with shared limited range wavelength converters(IEEE, 2007) Raffaelli, C.; Savi, M.; Akar, Nail; Karasan, EzhanShow more Application of synchronous optical switches in Optical Packet/Burst switched networks is considered. The shared per node architectural concept, where wavelength converters are shared among all input and output channels, is applied for contention resolution in the wavelength domain. A semi-analytical traffic model suitable to represent the different contributions to packet loss is proposed and validated. Full and limited range wavelength conversion capabilities are considered, and loss results obtained to support switch design. An approximated fully analytical approach for the limited range case is also described and comparison with simulation results is presented to assess the capability to capture the main aspects of packet loss behavior.Show more Item Open Access Performance analysis of an optical packet switch employing full/limited range share per node wavelength conversion(IEEE, 2007) Akar, Nail; Karasan, Ezhan; Muretto, G.; Raffaelli, C.Show more In this paper, we study an asynchronous optical packet switching node equipped with a number of limited range or full range wavelength converters shared per node. The packet traffic is realistically modeled by a superposition of a finite number of on-off sources as opposed to the traditional Poisson model which ignores the limited number of ports on a switch. We both study circular and non-circular limited range wavelength conversion schemes. In our simulations, we employ the far conversion policy where the optical packet is switched onto the farthest available wavelength in the tuning range, which is known to outperform the random conversion policy. We propose an approximate analytical method based on block tridiagonal Markov chains and fixed point iterations to solve for the blocking probabilities in share per node wavelength conversion systems. The method provides an accurate approximation for full range systems and acceptable results for limited range systems.Show more Item Open Access A reordering-free multipath traffic engineering architecture for DiffServ-MPLS networks(IEEE, 2003-10) Akar, Nail; Hokelek, İbrahim; Atik, Muammer; Karasan, EzhanShow more We propose a novel traffic engineering architecture for IP networks with multiprotocol label switching (MPLS) backbones. In this architecture, two (primary and secondary) label switched paths (LSPs) are established among every pair of IP routers located at the edge of an MPLS cloud. Traffic between a source-destination pair is then split between the primary and secondary LSPs using an ABR-like explicit-rate feedback gathered from the network. Taking into consideration the packet reordering effect of packet-based load balancing schemes, we propose a novel traffic splitting mechanism that operates on a per-flow basis. We show, using a variety of scenarios, that deploying flow-based multipath traffic engineering not only provides significantly and consistently better throughput than that of a single path, but is also void of any packet reordering. © 2003 IEEE.Show more Item Open Access Research on optical core networks in the e-Photon/ONe network of excellence(IEEE, 2006) Callegati, F.; Aracil, J.; Wosinska, L.; Andriolli, N.; Careglio, D.; Giorgetti, A.; Fdez-Palacios, J.; Gauger, C.; Klinkowski, M.; Gonzáles De Dios, O.; Hu, G.; Karasan, Ezhan; Matera, F.; Overby, H.; Raffaelli, C.; Rea, L.; Şengezer, Namık; Tornatore, M.; Vlachos, K.Show more This papers reports the advances in Optical Core networks research coordinated in the framework of the e-Photon/ONe and e-Photon/ONe+ networks of excellence.Show more Item Open Access Robust path design algorithms for traffic engineering with restoration in MPLS networks(IEEE, 2002-07) Yetginer, Emre; Karasan, EzhanShow more In this paper we study traffic engineering of restorable paths in multiprotocol label switching (MPLS) networks. We consider off-line computation of working and restoration paths with path rerouting as the restoration scheme. First we compute a link-disjoint path set for given set of demands. Using this path set we study four approaches for selecting working and restoration paths, and formulate each method as an integer linear programming (ILP) problem. A traffic uncertainty model is developed in order to compare these approaches based on their robustness with respect to changing traffic patterns. We obtain numerical results and compare these design approaches based on the number of additional demands carried and the distribution of residual capacity over the network. © 2002 IEEE.Show more Item Open Access Short-term propagation measurements and modeling for terrestrial line-of-sight links(IEEE, 2016) Göktaş, Polat; Topçu, Satılmış; Karasan, Ezhan; Altıntaş, Ayhan; Göktaş, Polat; Topçu, Satılmış; Karasan, Ezhan; Altıntaş, AyhanShow more This paper presents a propagation prediction technique to predict propagation mechanisms for fixed terrestrial line-of-sight (LOS) radio links, especially proposed for rural environments. We report the results of a short-term propagation measurement campaign carried out in the area of Ankara, Turkey. The field measurements were performed at the frequency of 2.536 GHz for a period of three months in summer 2015. It is observed that the difference between measurement data and predicted mean received power is smaller than the standard deviation value provided by Recommendation ITU-R P. 1546.Show more Item Open Access Subnetwork partitioning and section restoration in translucent optical networks(SPIE, 2003) Karasan, Ezhan; Arısoylu, M.Show more We discuss the problem of designing translucent optical networks composed of restorable, transparent subnetworks interconnected via transponders. We formulate the problem of designing restorable subnetworks in translucent networks as an Integer Linear Programming (ILP) problem, where the subnetworks are determined subject to the constraints that each subnetwork satisfies size limitations and it is 2-connected. A greedy heuristic algorithm for the same problem is also proposed for planar network topologies. We propose section restoration for translucent networks where failed connections are rerouted inside 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 section restoration generates fiber costs which are close to those with the path restoration technique for the mesh topologies used in this study. It is also shown that the number of transponders with the translucent optical network is substantially reduced compared to opaque networks.Show more Item Open Access Traffic engineering and regenerator placement in GMPLS networks with restoration(SPIE, 2002) Yetginer, Emre; Karasan, EzhanShow more 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 due to transmission impairments. We study a network architecture where there are regenerators at selected nodes and we propose two heuristic algorithms for the regenerator placement problem. Performances of these algorithms in terms of required number of regenerators and computational complexity are evaluated. In this network architecture with sparse regeneration, offline computation of working and restoration paths is studied with bandwidth reservation and 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. 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 due to traffic uncertainty that can be carried. Regenerator placement algorithms are also evaluated from a traffic engineering point of view.Show more Item Open Access TSCP: a tabu search algorithm for wavelength converting node placement in WDM optical networks(IEEE, 2005) Şengezer, Namık; Karasan, EzhanShow more Sparse wavelength conversion can increase the performance of all-optical wavelength division multiplexing (WDM) networks signi cantly by relaxing the wavelength continuity constraint. In this paper, we study the wavelength converter placement problem in multi- ber networks with static traf c demands. We present a tabu search based heuristic algorithm. The objective of the algorithm is to satisfy all the traf c demands with the minimum total cost of bers achieved in the full conversion case, by placing minimum number of wavelength converting nodes. We also implement a greedy algorithm and compare the performances of these converter placement algorithms with the optimum solutions on a sample network. The Tabu search based algorithm achieves the optimum solution in 72% of the test cases and it increases the average number of wavelength converting nodes by less than 10% with respect to the optimum solution. The effect of the utilized routing scheme on the generated solutions and the correlation between the converter node locations and the amount of traf c passing through the nodes are also investigated.Show more