• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3B
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• pp.375-390
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• 2004

Domain Name System(DNS), one of the most important Internet services, handles mapping from host names to Internet addresses and vice versa, and precedes many Internet applications such as Web, e-mail, file transfer, etc. In this paper, we propose a structural design of a generic name server system providing name services for a huge domain for the purpose of improving the performance as well as the reliability of the system. We demonstrate the validity of the design by implementing and running a testbed system. Our testbed employs a couple of master name sowers for distributing the service overhead over two, rather than one, servers and for achieving high availability of the system as a whole. We suggest the use of dynamic update to add and delete records from a zone for which the name server has authority. The slave name servers located remotely then get a new, updated copy of the zone via incremental zone transfers(IXFRs). The experiments with the implemented testbed show that the proposed structure would easily manage increasing demands on the server power, and be highly available in the face of transient faults of a module in the system.

• Convergence Security Journal
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• v.14 no.7
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• pp.53-58
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• 2014

MANET can quickly build a network because it is configured with only the mobile node and it is very popular today due to its various application range. However, MANET should solve vulnerable security problem that dynamic topology, limited resources of each nodes, and wireless communication by the frequent movement of nodes have. In this paper, we propose a domain-based distributed cooperative intrusion detection techniques that can perform accurate intrusion detection by reducing overhead. In the proposed intrusion detection techniques, the local detection and global detection is performed after network is divided into certain size. The local detection performs on all the nodes to detect abnormal behavior of the nodes and the global detection performs signature-based attack detection on gateway node. Signature DB managed by the gateway node accomplishes periodic update by configuring neighboring gateway node and honeynet and maintains the reliability of nodes in the domain by the trust management module. The excellent performance is confirmed through comparative experiments of a multi-layer cluster technique and proposed technique in order to confirm intrusion detection performance of the proposed technique.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.43 no.1 s.307
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• pp.91-100
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• 2006

A scheme is proposed for implementing the block LMS algorithm in a block floating point framework that permits processing of data over a wide dynamic range at a processor complexity and coat as low as that of a fixed point processor. The proposed scheme adopts appropriate formats for representing the filter coefficients and the data. Using these and a new upper bound on the step size, update relations for the filter weight mantissas and exponent are developed, taking care so that neither overflow occurs, nor are quantifies which are already very small multiplied directly. It is further shown how the mantissas of the filter coefficients and also the filter output can be evaluated faster by suitably modifying the approach of the fast block LMS algorithm

• Journal of Broadcast Engineering
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• v.17 no.6
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• pp.1014-1028
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• 2012

Recently, N-screen service and secondary device have gotten an attention from public. Also, we can experience N-screen service through various digital devices. N-screen means multimedia technology which can seamlessly consume multimedia content. Secondary device means auxiliary multimedia device which can consume content related to main content through adjunct connection to main device. Not only be electronic manufactures interested in N-screen technology and services but also digital devices applied for N-screen have been released. But it has limitation that user can only consume content to be purchased from content company server not device of user. This paper proposes the system that composes effective and various N-screen multimedia service through MPEG-4 LASeR (Lightweight Application Scene Representation) PMSI (Presentation and Modification of Structured Information) as international standard technology which can provide scene description including many instruction for dynamic update of scene.

• Smart Structures and Systems
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• v.13 no.4
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• pp.615-636
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• 2014

Aluminium Foam Sandwich (AFS) panels are becoming always more attractive in transportation applications thanks to the excellent combination of mechanical properties, high strength and stiffness, with functional ones, thermo-acoustic isolation and vibration damping. These properties strongly depend on the density of the foam, the morphology of the pores, the type (open or closed cells) and the size of the gas bubbles enclosed in the solid material. In this paper, the vibrational performances of two classes of sandwich panels with an Alulight(R) foam core are studied. Experimental tests, in terms of frequency response function and modal analysis, are performed in order to investigate the effect of different percentage of porosity in the foam, as well as the effect of the random distribution of the gas bubbles. Experimental results are used as a reference for developing numerical models using finite element approach. Firstly, a sensitivity analysis is performed in order to obtain a limit-but-bounded dynamic response, modelling the foam core as a homogeneous one. The experimental-numerical correlation is evaluated in terms of natural frequencies and mode shapes. Afterwards, an update of the previous numerical model is presented, in which the core is not longer modelled as homogeneous. Mass and stiffness are randomly distributed in the core volume, exploring the space of the eigenvectors.

• Journal of Korea Multimedia Society
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• v.11 no.8
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• pp.1129-1137
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• 2008

E-learning as a new education trend is being applied not only to cyber school but also various education fields such as employee training for companies or interactive learning for consumers. Users of the E-learning can take online tests individually anywhere, to evaluate their achievement level. Because users who are taking the online tests may show their own IDs or passwords to others, the possibility of cheating is very high. Therefore, it is very important to authenticate the users. In this paper, we propose an adaptive-keyboard authentication method which depends on user behavior patterns through the use of IDs and passwords. This method does not need any additional devices or special effort. An adaptive method to update patterns in which IDs and passwords are entered was previously suggested and this new method has proved to be better than previous methods through simulations and implementation.

• Journal of KIISE:Information Networking
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• v.31 no.3
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• pp.289-297
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• 2004

State-of-the-art wireless communication networks allow dynamic relocation of mobile terminals. A location management mechanism is required to keep track of a mobile terminal for delivering incoming calls. In this paper, we propose a fuzzy logic-based selective paging method to reduce paging cost. In the proposed fuzzy logic-based location management method, the location update uses the area-based method that uses direction-based together with movement-based methods, and the location search uses the fuzzy logic-based selective paging method based on the mobility information of mobile terminals. A partial candidate paging area is selected by fuzzy control rules, then the fuzzy logic-based selective paging method pages only the cells within the partial candidate paging area. The performance of proposed fuzzy logic-based location management method is to be evaluated by both an analytical model and a simulation, and is compared with those of LA and BVP methods. From these evaluation results, we know that the proposed fuzzy logic-based location management method provide better performance than other location management methods.

• Composites Research
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• v.12 no.1
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• pp.1-10
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• 1999

In order to predict the dynamic behavior of composite laminated plate accurately, the parametric identification is performed using its mechanical properties- $E_1,\;E_2,\;V_{12},\;G_{12}$ as design parameters. After natural frequencies are measured through simple vibration test, the objective function consists of the sum of errors between experimental and numerical frequencies of a structure. As optimization algorithm, conjugate gradient method is used to minimize the objective function. Sensitivity Analysis is performed to update design parameters during this process and can explain the result of parametric identification. In order to check the propriety of result, mode shapes are compared before and after identification. The improved prediction of natural frequencies of composite laminated plate is obtained with updated properties. For the application of result, updated properties is applied to the composite laminated plate that has different stacking sequence.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4C
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• pp.581-593
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• 2004

The interest in wireless LAN security is on the increase owing to a role of high-speed wireless Internet infrastructure of wireless LAN. Wi-Fi has released WPA standard in order to overcome drawbacks of WEP algorithm that is security element of current IEEE 802.11-based wireless LAN system. Pairwise key management and group key management in a mixed-mode which supports both terminals running WPA and terminals running original WEP security are very complicate. In this paper, we analyze flaws in WPA authenticator key management state machine for key distribution and propose the countermeasures to overcome the analyzed problems. Additionally, WPA authenticator key management state machine to which the solutions are applied is described. The reconstructed WPA authenticator key management state machine helps the AP perform efficiently group key exchange and group key update in the mixed-mode.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.10A
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• pp.736-745
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• 2009

The growth of mobile devices and the increase of using them have required the support of realtime multimedia application in wireless environments. Especially, wireless ad-hoc networks without central management system and with dynamically changing network topology need much researches of QoS routing for multimedia applications. However it is impossible to support the hard realtime QoS for these dynamic networks. In this paper, we propose a QoS routing scheme by using QoS DAG that is maintained by each mobile node and contains the QoS information for neighbor nodes. In order to maintain the QoS DAG, each node transmits its QoS information to neighbor nodes by local broadcasting, and the neighbor nodes update their QoS DAGs by the received message. In our proposed scheme, it is possible to search the QoS path efficiently by the QoS DAG without searching it in the whole network.