A. Halim Zaim

Istanbul University, İstanbul, Istanbul, Turkey

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Publications (29)7.21 Total impact

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    ABSTRACT: In parallel with the enormous spread of Internet usage, the tendency of users for high capacity applications (HDTV, Online Games, P2P File Transfer) are rising. This increase in needs of data communication, compel the service providers to act to end users better than before. At this point, Passive Optical Networks (PONs) distinguish in access network solutions due to its capability of carrying high amount of data over longer distances. Although they are still in development, existing electronic based data communication techniques (ADSL, double twisted copper telephony systems like VDSL, cable modem coaxial cable CATV systems) can operate over short distances and have large amount of energy consumption. In this paper, basic schemes of dynamic bandwidth allocation algorithms on EPON have been presented and a novel online-offline based method called hcDBA (Half Cycling Dynamic Bandwidth Allocation) has been introduced. In addition, hcDBA algorithm has been improved with early prediction mechanism (p-hcDBA). By the simulation studies, it has been investigated that hcDBA algorithm performs better than existing mechanism in terms of byte loss ratio and access delays criteria. p-hcDBA also improved the performance in terms of access delay. In this study, we stated that when the bandwidth increases the prediction approached has more impact of the overall performance.
    Optical Switching and Networking 01/2014; · 0.72 Impact Factor
  • Taner Çevik, Abdül Halim Zaim
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    ABSTRACT: Depending upon the technological developments, the same fast evolution has occurred in the structures of sensor networks, their composing devices which are sensor nodes, and their application areas. Those tiny, energy-constrained, mostly non-real-time data transmitting sensor nodes have evolved to more energy-containing, camera-adapted, real-time multimedia-data-transmitting devices. Developments in the usage areas and the capabilities have revealed some other problems such as time limited data transmission. In this paper, we propose a multichannel cross-layer architecture for Quality of Service (QoS) constrained multimedia sensor networks. The proposed architecture considers both the time and energy efficiency concepts. Energy efficiency is succeeded by ensuring the fair load distribution among the nodes during a real-time multimedia packet stream transmission. Besides ensuring the fair load distribution, on-time packet transmission is also assured by constructing the paths with a hard reservation technique depending on the predetermined QoS constraints. Simulations show that the proposed architecture provides higher performance than the Greedy approach and the LEERA scheme.
    International Journal of Distributed Sensor Networks 03/2013; 2013. · 0.73 Impact Factor
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    ABSTRACT: This study is about a prediction approach for our previous dynamic bandwidth allocation algorithm for Ethernet Passive Optical Networks (EPON). Our previous work (hcDBA) is based on half cycle timing for bandwidth allocation. That can be handled as a middle way between online and offline bandwidth allocation schemes. In PONs, prediction is used for bandwidth allocation to grant loaded nodes with early responses. However, due to the versatile nature of data traffic, prediction algorithms have a handicap to provide a better solution in classical approaches. In this study, a novel prediction approach integrated with hcDBA algorithm described. Performance comparison of hcDBA with & without prediction and IPACT algorithm is given. According to the simulation results, prediction on hcDBA seems to give some performance improvements in terms of access-delay.
    Computers and Communications (ISCC), 2012 IEEE Symposium on; 01/2012
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    ABSTRACT: Metropolitan ring networks are usually used to connect the high speed backbone networks with access networks. Until now, the metropolitan network and the access network are gained much attention of researchers. However they have been investigated in separate ways. There is no work in which the end- to-end performance from end-users of the access network to metropolitan network is evaluated. How to simulate a complete end-to-end network while keeping basic characteristics of access and metro traffic is an emergence problem to evaluate the end-to- end performance. In reality, a complete end-to-end network in which hundreds of Ethernet Passive Optical Network (EPON) are connected to metro ring networks cannot be simulated because of the huge amount of traffic generated from the access network side. In this paper, we aim to obtain trace files of incoming traffic at the entrance of Optical Line Terminal (OLT) by running simulations of an EPON network which implements Interleaved Polling with Adaptive Cycle Time (IPACT). Then, the generated traffic pattern will be characterized in order to find corresponding traffic model among well known traffic models and this model will be used as output traffic of OLTs. After, we can use this traffic model without simulating a complete EPON network. Through various simulations, we observe that the generated traffic that comes to OLT is similar to the traffic obtained with Poisson sources.
    Proceedings of the 7th International Wireless Communications and Mobile Computing Conference, IWCMC 2011, Istanbul, Turkey, 4-8 July, 2011; 01/2011
  • Taner Cevik, A. Halim Zaim
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    ABSTRACT: With the evolution of electronics, wireless sensor networks have been very popular in many domains of human life such as health, industry and military. This popularity has taken the attention on to the researches about wireless sensor networks. Wireless Sensor Networks are especially very favorable in conditions where it is physically difficult and dangerous for human being to gather information. Therefore, lifetime of those networks must be prolonged as much as possible, since it will be also infeasible to replace the energy depleted sensors with the new ones deployed in such geographical areas that are difficult and dangerous for human being to enter. In this paper, we present a localized energy aware routing method LEERA-MS and an alternative LEERA-MS-TH method that are used incorporation with an energy efficient sleep-wakeup schedule which is included with pipelining mechanism we have proposed before. Employing multiple sinks improve the performance by providing the fairly distribution of the load. Simulation results show that this routing method applied on a multiple sinks topology when employed together with the pipelined sleep-wakeup schedule provides 40% longer lifetime for wireless sensor networks.
    Distributed Computing in Sensor Systems, 7th IEEE International Conference and Workshops, DCOSS 2011, Barcelona, Spain, 27-29 June, 2011, Proceedings; 01/2011
  • Computer and Information Sciences II - 26th International Symposium on Computer and Information Sciences, London, UK, 26-28 September 2011; 01/2011
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    Taner Cevik, Derya Yiltas, A. Halim Zaim
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    ABSTRACT: Wireless sensor networks are comprised of energy constraint, battery powered small devices that sense the environment and transmit the data to the sink in order to take action according to data. Since the sensors are small energy constraint devices energy consumption is the main problem for wireless sensor networks. Energy spent during data communication is much more than spent during in-sensor computing. Most of the effort is spent on designing protocols in order to conserve energy. This paper proposes an improved version of energy efficient MAC protocol STEM by including pipelining mechanism. Results show that the proposed method overperform the original version of STEM by sustaining less delay.
    Procedia CS. 01/2011; 3:96-103.
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    Networked Digital Technologies - Second International Conference, NDT 2010, Prague, Czech Republic, July 7-9, 2010. Proceedings, Part II; 01/2010
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    ABSTRACT: In this article, we are interested in improving the handover quality of Host Identity Protocol (HIP) in the case of micro mobility by (i) proposing the Local Rendezvous Server architecture as a first attempt to minimize the handover delay in the mobility process, (ii) introducing an adaptive early update mechanism to improve the handover quality during mobility by introducing early HIP (eHIP) and finally (iii) we propose a method that minimizes the total radio resource utilization in our architecture subject to the QoS constraints of Mobile Nodes (MNs) especially the delay of real-time applications. We prove through simulations that our scheme can achieve significant gains in terms of radio resource utilization while taking into account the mobility of MNs along with the respect of their QoS parameters for their ongoing real-time applications.
    Proceedings of the IEEE 21st International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2010, 26-29 September 2010, Istanbul, Turkey; 01/2010
  • International Journal of Computer Science Issues(IJCSI). 01/2010; 7(5).
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    ABSTRACT: This article presents a comparative study between Optical Burst Switching (OBS) and Optical Packet Switching (OPS) with variable-size packets on mono-service and multi-service network with Quality of Service (QoS) support. In terms of performance criteria, loss rate in byte and access delay are considered. A 2-state Markov Modulated Poisson Process (MMPP) traffic generator is used. A 14-nodes mesh network topology illustrating NSFNET and a ring topology are designed as the testbed. NS2 Network Simulation tool is used for our tests. According to the simulation results, we have seen that in both mono-service and multi-service networks, OPS is better than OBS under low traffic loads. However, OBS performs better than OPS in mono-service networks and low priority service classes under high traffic loads. In this study, we have shown that choosing one of these two switching technologies (OPS or OBS) in the future depends on the traffic load and the topology of network, together with the considered service differentiation scheme.
    Optical Switching and Networking. 01/2010; 7:85-94.
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    ABSTRACT: Intrusions detection systems (IDSs) are systems that try to detect attacks as they occur or after the attacks took place. IDSs collect network traffic information from some point on the network or computer system and then use this information to secure the network. Intrusion detection systems can be misuse-detection or anomaly detection based. Misuse-detection based IDSs can only detect known attacks whereas anomaly detection based IDSs can also detect new attacks by using heuristic methods. In this paper we propose a hybrid IDS by combining the two approaches in one system. The hybrid IDS is obtained by combining packet header anomaly detection (PHAD) and network traffic anomaly detection (NETAD) which are anomaly-based IDSs with the misuse-based IDS Snort which is an open-source project.The hybrid IDS obtained is evaluated using the MIT Lincoln Laboratories network traffic data (IDEVAL) as a testbed. Evaluation compares the number of attacks detected by misuse-based IDS on its own, with the hybrid IDS obtained combining anomaly-based and misuse-based IDSs and shows that the hybrid IDS is a more powerful system.
    Computers & Electrical Engineering. 01/2009; 35:517-526.
  • Derya Yiltas, A. Halim Zaim
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    ABSTRACT: All communication systems must be controlled by strong traffic management architectures. In such systems, many calls are transmitted through many nodes. In this way, a call is blocked if the system is overloaded or the link between the current nodes is deactivated. In this study, we analyze and control the traffic of our sample communication system under different criteria to avoid these problems. We consider low-earth orbit (LEO) satellite systems, because satellites become a vital requirement for today's dense communication areas. We present a mathematical model to calculate call blocking probabilities (CBPs) with a new traffic density function which is based on coverage areas and current time slots. We also use the channel numbers of the links between satellites in CBP formulas to specify the communication lines and to mean different delivery buses for the calls. Then we compare the results under different CBP values.
    Proceedings of the International Conference on Wireless Communications and Mobile Computing: Connecting the World Wirelessly, IWCMC 2009, Leipzig, Germany, June 21-24, 2009; 01/2009
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    ABSTRACT: In current internet architecture, IP address plays both roles of locator and identification of attached nodes in the network. As the mobility of devices increases, the dual role of IP addresses makes mobility management complicated from security and QoS point of views. Host Identity Protocol (HIP) proposed by the IETF and IRTF introduces a new approach to solve the problem of IP addresses' dual role. HIP introduces the concept o identifier being different from the IP address to identify uniquely the node, no matter which IP address it has. The network keeps the correspondence between this HIP identifier and the current IP address of the mobile node. In this paper, we examined the micro mobility issues and challenges of HIP and we propose a hierarchical approach to improve the HIP update process and a new early update mechanism in order to improve the handover latency.
    Proceedings of the 6th International Conference on Mobile Technology, Applications, and Systems, Mobility Conference 2009, Nice, France, September 2-4, 2009; 01/2009
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    ABSTRACT: In this study, a wavelength grouping approach has been proposed for core nodes in OBS in order to control byte drop rates for different classes of traffic. Preemptive Channel Scheduling Algorithm (PCSA) has been used for channel scheduling in OBS. In terms of performance criteria, loss rate in bytes is considered. A 2-state MMPP (Markov Modulated Poisson Process) traffic generator on a 14-node mesh network topology illustrating NSFNET is designed as the testbed. NS2 Network Simulation tool is used for our tests. In OBS algorithms, bursts are created using a hybrid model that takes into account both timeout and maximum length threshold mechanisms. In nodes, in order to satisfy QoS requirements, priority based queuing and Regulative Wavelength Grouping (RWG) are used. In priority based queuing, packets (bursts) are sent according to their priority order. RWG mechanism, where the number of wavelengths for each traffic class is arranged for adjusting the packet drop probability of different classes of client traffic under a specific threshold value, is used for providing priority levels. According to the simulation studies, RWG algorithm gives better results in OBS for high priority traffic performance.
    The Fifth Advanced International Conference on Telecommunications, AICT 2009, 24-28 May 2009, Venice/Mestre, Italy; 01/2009
  • Derya Yiltas, A. Halim Zaim
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    ABSTRACT: In this paper, we present a new method for calculating call blocking probabilities (CBPs) in a low Earth orbit satellite network that carries voice calls. The calculation of the CBPs uses the Erlang-B formula, but the traffic intensity has been modified to take into the time and location in which the calls are made. Copyright © 2009 John Wiley & Sons, Ltd.
    International Journal of Satellite Communications and Networking 01/2009; 27:103-115. · 0.54 Impact Factor
  • Derya Yiltas, A. Halim Zaim
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    ABSTRACT: Since the satellites become more common for today's communication area, the process and the improvements in the satellite networks are gaining importance. One of the challenges in satellite networks is the routing operation between two end nodes, because, these networks have dynamic changing satellite movements. During these movements, a satellite can give its coverage area service order to one of its neighboring satellites. Also some calls can be blocked when the call densities exceed the communication link's capacities or the signals interfere with each other. All of these situations make the routing operation quite complicated. In this study, we design a new routing algorithm for low-earth orbit (LEO) satellite systems. We use dynamic satellite topologies containing different number of nodes. We apply the genetic algorithms during the optimization steps. We introduce a new objective function including the delay and the aging factor as the characteristic properties of the paths. Finally, we compare the paths with each other and select the optimal path having the best fitness value.
    01/2008;
  • D. Yiltas, A.H. Zaim
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    ABSTRACT: Routing algorithms constitute an important area for the packet transmission in satellite networks. There are many studies about static routing algorithms in which the satellite systems are thought to be fixed on the sky. Thus the routing operation is made over a fixed topology in these studies. However in real world, the satellites move continuously in their orbits along the communications. So the dynamic routing is the most appropriate routing type for real applications. In this study, we investigated several routing algorithms and designed a new dynamic routing algorithm. Our path selections are based on the genetic algorithms through a new fitness function. Also we computed the call blocking probabilities (CBPs) of all links on the paths formed the route of a packet transmission.
    Recent Advances in Space Technologies, 2007. RAST '07. 3rd International Conference on; 07/2007
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    Kirci Pinar, A. Halim Zaim
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    ABSTRACT: Optical burst switch (OBS) is considered to be a promising switch technology for the future network. In this paper, just-in-time (JIT), just-enough-time (JET) and horizon signalling schemes for OBS are presented. These signalling schemes run over a core dynamic wavelength division multiplexing (DWDM) network. The network is proposed to support IP, ATM and burst traffic. We apply the Poisson and self-similar models to identify inter-arrival times in these protocols and the burst contention is handled by burst dropping. As a result, the variety of the simulation results show the pros and cons of the evaluated JIT, JET and horizon signalling schemas.
    Optica Applicata. 01/2006;
  • P. Kirci, A.H. Zaim
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    ABSTRACT: In this paper, we give an overview of all-optical networks. The classification of optical burst switched networks (OBS) which is one of the WDM schemes is proposed. We compare the performance of different traffic models on definite signaling protocols of OBS. These traffic models are IP/burst and multimedia traffic. As multimedia traffic we evaluate the performance of video traffic through all-optical network. We also investigate the affects of other traffics and network characteristics on application performance. The examined signaling protocols are JIT, JET and Horizon. We apply the exponential and hyperexponential distributions on these traffics for producing the inter-arrival times of the packets. We present a communication between a source client node and a destination client node over an ingress and one or more multiple intermediate switches. Our paper also includes burst setup, burst setup ack and keepalive message types. We propose a framework for calculating the dropping rates. As a result, we compare the signaling protocols according to the burst drop rates
    Computer Networks, 2006 International Symposium on; 01/2006