Computer Engineering / Bilgisayar Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/10
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Conference Object Citation - WoS: 11Citation - Scopus: 20Learning Styles Diagnosis Based on Learner Behaviors in Web Based Learning(Springer Verlag, 2009) Atman, Nilüfer; İnceoğlu, Mustafa Murat; Aslan, Burak GalipIndividuals have different backgrounds, motivation and preferences in their own learning processes. Web-based systems that ignore these differences have difficulty in meeting learners' needs effectively. One of these individual differences is the learning style. For providing adaptively incorporated learning styles, firstly learning styles of learners have to be identified. There are many different learning models in literature. This study is based on Felder and Silverman's Learning Styles Model and investigates only active/reflective and visual/verbal dimensions of this model. Instead of filling out a questionnaire, learner behaviors are analyzed with the help of literature-based approaches so that learning styles of learners can be detected.Article Optimal Control for Real-Time Feedback Rate-Monotonic Schedulers(Springer Verlag, 2005) Ayav, Tolga; Ferrari-Trecate, GiancarloThis paper presents an optimal control scheme for a real-time feedback control rate-monotonic scheduling (FC-RMS) system. We consider two-version tasks composed of a mandatory and an optional part to be scheduled according to the FC-RMS. In FC-RMS, the controller provides a feedback strategy for deciding about the execution or rejection of the optional sub-tasks. By modeling the task execution times as random variables, we first find the statistical model of FC-RMS and then we design a pure optimal controller and an optimal controller with feedforward integral compensation. The comparison of these two schemes with common Proportional-Integral-Derivative (PID) controller highlights the benefit of the optimal scheme with integral compensation. The results are demonstrated through the real implementation of FC-RMS on RT-Linux.Conference Object Citation - WoS: 12Citation - Scopus: 20A Hierarchical Leader Election Protocol for Mobile Ad Hoc Networks(Springer Verlag, 2008) Dağdeviren, Orhan; Erciyeş, KayhanLeader Election is an important problem in mobile ad hoc networks and in distributed computing systems. In this study, we propose a hierarchical, cluster based protocol to elect a leader in a mobile ad hoc network. The initial phase of the protocol employs a clustering algorithm to group nodes of the network after which a leader for a cluster(clusterhead) is elected. The second phase is performed by forming a connected ring of these leaders using the Ring Formation Algorithm. Finally, Chang Roberts Leader Election Algorithm for rings is employed in the final phase to elect the super-leader among the clusterheads. We provide performance results of this protocol for various mobility parameters and analyze its time and message complexities.Conference Object Citation - WoS: 13Citation - Scopus: 12Distributed Algorithms To Form Cluster Based Spanning Trees in Wireless Sensor Networks(Springer Verlag, 2008) Erciyeş, Kayhan; Özsoyeller, Deniz; Dağdeviren, OrhanWe propose two algorithms to form spanning trees in sensor networks. The first algorithm forms hierarchical clusters of spanning trees with a given root, the sink. All of the nodes in the sensor network are then classified iteratively as subroot, intermediate or leaf nodes. At the end of this phase, the local spanning trees are formed, each having a unique subroot (clusterhead) node. The communication and data aggregation towards the sink by an ordinary node then is accomplished by sending data to the local subroot which routes data towards the sink. A modified version of the first algorithm is also provided which ensures that the obtained tree is a breadth-first search tree where a node can modify its parent to yield shorter distances to the root. Once the sub-spanning trees in the clusters are formed, a communication architecture such as a ring can be formed among the subroots. This hybrid architecture which provides co-existing spanning trees within clusters yields the necessary foundation for a two-level communication protocol in a sensor network as well as providing a structure for a higher level abstraction such as the γ synchronizer where communication between the clusters is performed using the ring similar to an α synchronizer and the intra cluster communication is accomplished using the sub-spanning trees as in the β synchronizers. We discuss the model along with the algorithms, compare them and comment on their performances.Conference Object Citation - WoS: 1Citation - Scopus: 3A Replication-Based Fault Tolerance Protocol Using Group Communication for the Grid(Springer Verlag, 2006) Erciyeş, KayhanWe describe a replication-based protocol that uses group communication for fault tolerance in the Computational Grid. The Grid is partitioned into a number of clusters and each cluster has a designated coordinator that manages the states of the replicas within its cluster. The coordinators belong to a process group and the proposed protocol ensures the correct sequence of message deliveries to the replicas by the coordinators. Any failing node of the Grid is replaced by an active replica to provide correct continuation of the operation of the application. We show the theoretical framework along with illustrations of the replication protocol and its implementation results and analyze its performance and scalability.Conference Object Citation - WoS: 6Citation - Scopus: 6A Merging Clustering Algorithm for Mobile Ad Hoc Networks(Springer Verlag, 2006) Dağdeviren, Orhan; Erciyeş, Kayhan; Çokuslu, DenizClustering is a widely used approach to ease implementation of various problems such as routing and resource management in mobile ad hoc networks (MANET)s. We propose a new fully distributed algorithm for clustering in MANETs that merges clusters to form higher level clusters by increasing their levels. We show the operation of the algorithm and analyze its time and message complexities and provide results in the simulation environment of ns2. Our results conform that the algorithm proposed is scalable and has a lower time and message complexities than the other algorithmsConference Object Citation - WoS: 8Citation - Scopus: 13A Distributed Backbone Formation Algorithm for Mobile Ad Hoc Networks(Springer Verlag, 2006) Dağdeviren, Orhan; Erciyeş, KayhanConstruction of a backbone architecture is an important issue in mobile ad hoc networks(MANET)s to ease routing and resource management. We propose a new fully distributed algorithm for backbone formation in MANETs that constructs a directed ring architecture. We show the operation of the algorithm, analyze its message complexity and provide results in the simulation environment of ns2. Our results conform that the algorithm is scalable in terms of its running time and roundtrip delay against mobility, surface area, number of nodes and number of clusterheads.Conference Object Citation - WoS: 1Citation - Scopus: 1Performance Evaluation of Group Communication Architectures in Large Scale Systems Using Mpi(Springer Verlag, 2006) Erciyeş, Kayhan; Dağdeviren, Orhan; Payli, Reşat ÜmitGroup communication is an important paradigm for fault tolerance in large scale systems. We describe various group architectures as pipelined, hierarchical, daisy and hypercube groups each consisting of separate clusters, investigate the theoretical performance bounds of these architectures and evaluate their experimental performances using MPI group communication primitives. We first derive time bounds for multicast message deliveries in these architectures and then provide tests to measure the times taken for the same operation. The multicast message delivery times are tested against the number of clusters within a group and the size of the multicast message. We conclude that daisy architecture is favorable both in terms of delivery times and message sizes theoretically and experimentally.Conference Object Citation - WoS: 23Citation - Scopus: 31A Dominating Set Based Clustering Algorithm for Mobile Ad Hoc Networks(Springer Verlag, 2006) Çokuslu, Deniz; Erciyeş, Kayhan; Dağdeviren, OrhanWe propose a new Connected Dominating Set (CDS) based algorithm for clustering in Mobile Ad hoc Networks (MANETs). Our algorithm is based on Wu and Li's [14] algorithm, however we provide significant modifications by considering the degrees of the nodes during marking process and also provide further heuristics to determine the color of a node in the initial phase. We describe, analyze and measure performance of this new algorithm by simulation and show that it performs better than Wu and Li's [14] algorithm especially in the case of dense networks.Article Citation - WoS: 4Citation - Scopus: 9End-To Security Implementation for Mobile Devices Using Tls Protocol(Springer Verlag, 2006) Kayayurt, Barış; Tuğlular, TuğkanEnd-to-end security has been an emerging need for mobile devices with the widespread use of personal digital assistants and mobile phones. Transport Layer Security Protocol (TLS) is an end-to-end security protocol that is commonly used on the Internet, together with its predecessor, SSL protocol. By implementing TLS protocol in the mobile world, the advantage of the proven security model of this protocol can be utilized. The main design goals of mobile end-to-end security protocol are maintainability and extensibility. Cryptographic operations are performed with a free library, Bouncy Castle Cryptography Package. The object oriented architecture of proposed end-to-end security protocol implementation makes the replacement of this library with another cryptography package easier. The implementation has been experimented with different cases, which represent use of different cryptographic algorithms.