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Çağlar, Mine

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Çağlar

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Researcher Of Publications: search.filters.isAuthorOfPublication.5f26aa47-238a-4dfb-b304-e3ed053f45e9

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Now showing 1 - 10 of 57
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    An analytical model based on G/M/1 with self-similar input to provide end-to-end QoS in 3G networks
    (Association for Computing Machinery (ACM), 2006) Iftikhar, M.; Landfeldt, B.; Department of Mathematics; Çağlar, Mine; Faculty Member; Department of Mathematics; College of Sciences; 105131
    The dramatic increase in demand for wireless Internet access has lead to the introduction of new wireless architectures and systems including 3G, Wi-Fi and WiMAX. 3G systems such as UMTS and CDMA2000 are leaning towards an all-IP architecture for transporting IP multimedia services, mainly due to its scalability and promising capability of inter-working heterogeneous wireless access networks. During the last ten years, substantial work has been done to understand the nature of wired IP traffic and it has been proven that IP traffic exhibits self-similar properties and burstiness over a large range of time scales. Recently, because of the large deployment of new wireless architectures, researchers have focused their attention towards understanding the nature of traffic carried by different wireless architecture and early studies have shown that wireless data traffic also exhibits strong long-range dependency. Thus, the classical tele-traffic theory based on a simple Markovian process cannot be used to evaluate the performance of wireless networks. Unfortunately, the area of understanding and modeling of different kinds of wireless traffic is still immature which constitutes a problem since it is crucial to guarantee tight bound QoS parameters to heterogeneous end users of the mobile Internet. In this paper, we make several contributions to the accurate modeling of wireless IP traffic by presenting a novel analytical model that takes into account four different classes of self-similar traffic. The model consists of four queues and is based on a G/M/1 queueing system. We analyze it on the basis of priority with no preemption and find exact packet delays. To date, no closed form expressions have been presented for G/M/1 with priority.
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    Maximum loss and maximum gain of spectrally negative Levy processes
    (Springer, 2017) Vardar-Acar, Ceren; Department of Mathematics; Çağlar, Mine; Faculty Member; Department of Mathematics; College of Sciences; 105131
    The joint distribution of the maximum loss and the maximum gain is obtained for a spectrally negative L,vy process until the passage time of a given level. Their marginal distributions up to an independent exponential time are also provided. The existing formulas for Brownian motion with drift are recovered using the particular scale functions.
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    Principles and performance analysis of second: a system for epidemic peer-to-peer content distribution
    (Academic Press Ltd- Elsevier Science Ltd, 2009) N/A; Department of Computer Engineering; Department of Mathematics; Department of Computer Engineering; Özkasap, Öznur; Çağlar, Mine; Alagöz, Ali; Faculty Member; Faculty Member; Other; Department of Mathematics; Department of Computer Engineering; College of Engineering; College of Sciences; College of Engineering; 113507; 105131; N/A
    We propose and design a peer-to-peer system, SeCond, addressing the distribution of large sized content to a large number of end systems in an efficient manner. In contrast to prior work, it employs a self-organizing epidemic dissemination scheme for state propagation of available blocks and initiation of block transmissions. in order to exploit heterogeneity of peers, enhance the utilization of system resources and for the ease of deployment, scalability, and adaptivity to dynamic peer arrivals/departures, we propose mechanisms for adjusting protocol parameters dynamically according to the bandwidth usages. We describe design and analysis details of our protocol SeCond. Comprehensive performance evaluations and comparison with the BitTorrent system model have been accomplished for a wide range of scenarios. Performance results include scalability analysis for different arrival/departure patterns, flash-crowd scenario, overhead analysis, and fairness ratio. The major metrics we study include the average file download time, load on the primary seed, uplink/downlink utilization. and communication overhead. We show that SeCond is a scalable and adaptive protocol which takes the heterogeneity of the peers into account. The protocol is as fair as BitTorrent although it has no explicit strategy addressing free-riding. We also illustrate the applicability of an analytical fluid model to the behavior of SeCond.
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    Multicast transport protocol analysis: self-similar sources
    (Springer-Verlag Berlin, 2004) Department of Mathematics; Department of Computer Engineering; Çağlar, Mine; Özkasap, Öznur; Faculty Member; Faculty Member; Department of Mathematics; Department of Computer Engineering; College of Sciences; College of Engineering; 105131; 113507
    We study the traffic that scalable multicast protocols generate in terms of message delays over the network as well as traffic counts at the link level in the case of self-similar sources. In particular, we study Bimodal Multicast and Scalable Reliable Multicast protocols proposed for scalable reliable multicasting. These protocols are based on different mechanisms for recovering from message losses and providing scalability. We discuss the protocol mechanisms as the main underlying factor in our empirical results. Our results can be considered as a contribution to the general problem of integration of multicast communication to large scale.
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    Stepwise probabilistic buffering for epidemic information dissemination
    (Institute of Electrical and Electronics Engineers (IEEE), 2006) N/A; Department of Mathematics; Department of Computer Engineering; Ahi, Emrah; Çağlar, Mine; Özkasap, Öznur; Master Student; Faculty Member; Faculty Member; Department of Mathematics; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; 105131; 113507
    For large-scale peer-to-peer applications, bioinspired epidemic protocols have considerable advantages as they are robust against network failures, scalable and provide probabilistic reliability guarantees. While providing reliability, a key issue to consider is the usage of system wide buffer space. In this context, we introduce a novel scheme called stepwise probabilistic buffering that reduces the amount of buffering and distributes the load of buffering to the entire system where every peer does not have the complete view of the system. We compute the performance measures through simulations of large-scale application scenarios.
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    The energy spectrum of stochastic eddies with gamma distribution
    (Natural Sciences Publishing, 2015) Kara, Rukiye; Department of Mathematics; Çağlar, Mine; Faculty Member; Department of Mathematics; College of Sciences; 105131
    Çinlar velocity field which is based on eddies of rotational form is a promising subgrid velocity model for its use in large eddy simulation (LES). This has been confirmed by data analysis of high frequency radar observations. The energy spectrum plays a central role for representing the subgrid scales in filtered Navier-Stokes equations used in LES. We consider a truncated Gamma distribution for eddy sizes to replicate the subgrid scale energy spectrum analytically. Kolmogorov proposed a form of the spectrum that extends to the inertial scale. Lundgren vortex has a spectrum involving an exponential function and has been used in LES. Çinlar velocity spectrum which is based on the truncated Gamma distribution indicates a good match with the spectrum estimated from real data. The results of this study can be used for designing a method for representing the small scale structures in LES by modeling the subgrid stress.
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    An alternating service model with self-similar input to provide guaranteed QoS in wireless internet
    (IEEE, 2006) Iftikhar, Mohsin; Landfeldt, Bjorn; Department of Mathematics; Çağlar, Mine; Faculty Member; Department of Mathematics; College of Sciences; 105131
    Over the past few years, we have witnessed a growing popularity of new wireless architectures such as 3G, WiFi and Wi-Max due to the increase in demand for wireless Internet access. The all-IP based future mobile and wireless network model is expected to be the most dominant architecture for QoS provisioning in next-generation wireless networks, mainly due to its scalability and capability of inter-working heterogeneous wireless access networks. Recently, the rapid growth of various wireless infrastructures and the interesting mixture of wireless traffic generated by large number of devices (PDAs, Laptops and cell-phones) have diverted the attention of wireless research community towards understanding the nature of traffic carried by different wireless architectures. A series of recent studies on GPRS aggregated traffic, WAP and Web traffic has proven that wireless traffic exhibits strong long-range dependency. However, much of the current understanding of wireless traffic modeling builds on classical Poisson distributed traffic, which can yield misleading results and hence poor wireless network planning. In this paper, we contribute to the accurate modeling of wireless IP traffic by considering two different types of traffic that exhibit long-range dependency and self-similarity. We consider a model of two queues based on G/M/1 queueing system and analyze it on the basis of 1-limited polling service and find exact bounds on packet delay.
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    Topology dependent information dissemination in P2P networks for anti-entropy algorithmS
    (Ieee, 2008) N/A; N/A; Department of Computer Engineering; Department of Mathematics; İskender, Emre; Özkasap, Öznur; Çağlar, Mine; Master Student; Faculty Member; Faculty Member; Department of Computer Engineering; Department of Mathematics; Graduate School of Sciences and Engineering; College of Engineering; College of Sciences; N/A; 113507; 105131
    Analyzing the behavior of epidemic spreading in a network is a good way of modeling several network phenomena. There are several studies analyzing the spreading of email viruses. Spreading of epidemics is also a good model for several types of information dissemination in distributed systems. In this study, we examine spreading of epidemics for anti-entropy algorithms in a peer-to-peer network with any given topology. We derive nodes' exact probability distributions of being infected in each epidemic cycle.
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    Topology dependent information dissemination in P2P networks for anti-entropy algorithms
    (IEEE, 2008) N/A; Department of Computer Engineering; Department of Mathematics; Özkasap, Öznur; Çağlar, Mine; İskender, Emre; Faculty Member; Faculty Member; Master Student; Department of Computer Engineering; Department of Mathematics; College of Engineering; College of Sciences; Graduate School of Sciences and Engineering; 113507; 105131; N/A
    Analyzing the behavior of epidemic spreading in a network is a good way of modeling several network phenomena. There are several studies analyzing the spreading of email viruses. Spreading of epidemics is also a good model for several types of information dissemination in distributed systems. In this study, we examine spreading of epidemics for anti-entropy algorithms in a peer-to-peer network with any given topology. We derive nodes' exact probability distributions of being infected in each epidemic cycle.
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    On the modeling of CO2 EUA and CER prices of EU-ETS for the 2008-2012 period
    (Wiley, 2016) Gürler, Ülkü; Yenigün, Deniz; Berk, Emre; Department of Mathematics; Çağlar, Mine; Faculty Member; Department of Mathematics; College of Sciences; 105131
    Increased consumption of fossil fuels in industrial production has led to a significant elevation in the emission of greenhouse gases and to global warming. The most effective international action against global warming is the Kyoto Protocol, which aims to reduce carbon emissions to desired levels in a certain time span. Carbon trading is one of the mechanisms used to achieve the desired reductions. One of the most important implications of carbon trading for industrial systems is the risk of uncertainty about the prices of carbon allowance permits traded in the carbon markets. In this paper, we consider stochastic and time series modeling of carbon market prices and provide estimates of the model parameters involved, based on the European Union emissions trading scheme carbon allowances data obtained for 2008-2012 period. In particular, we consider fractional Brownian motion and autoregressive moving average-generalized autoregressive conditional heteroskedastic modeling of the European Union emissions trading scheme data and provide comparisons with benchmark models. Our analysis reveals evidence for structural changes in the underlying models in the span of the years 2008-2012. Data-driven methods for identifying possible change-points in the underlying models are employed, and a detailed analysis is provided. Our analysis indicated change-points in the European Union Allowance (EUA) prices in the first half of 2009 and in the second half of 2011, whereas in the Certified Emissions Reduction (CER) prices three change-points have appeared, in the first half of 2009, the middle of 2011, and in the second half of 2012. These change-points seem to parallel the global economic indicators as well.