• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.4A
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• pp.304-311
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• 2005

OCSP has specific characters which can suspend, close, and correct in real time. But, as more clients use the OCSP server verification, more updated information is needed, which can lead to jamming in the OCSP server. To apply this technique of Distributed OCSP server so as to reduce the certificate verification OCSP from jamming. Also, the Distributed OCSP server will solve the problems of the intensive central structure. Simulation results show that the average reply time of certificate verification request and server load are reduced in the case using distributed OCSP. In addition to this advantage, resource distribution and fault tolerance are acquired because of multiple OCSP.

• Journal of Biomedical Engineering Research
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• v.6 no.1
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• pp.55-64
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• 1985

The cardiac activation process using three dimensional ventricular model is simulated.To study this theme, we constructed a cardiac ventricular model and simulated the cardiac activation process using the action potential duration and the activation time. The cardiac ventricular model is generated by the logical combination of the elliptic equations. The action potential duration could be obtained from the fact that it is linearly distributed between model cells. The cardiac activation process was simulated by the law of "all-or-none" Based on the activation time and the action potential do-ration the cardiac potential at the arbitrary time after the activation of the model cell was computed. To test the validity of model, the comparison of the results of model simulation with the physiological data was performed. In conclusion, this model shows the simular results which is comparable to the real conduction of the cardiac excitation.xcitation.

• Journal of the Korea Society for Simulation
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• v.9 no.3
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• pp.1-11
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• 2000

This paper proposes the practical echo-signal synthesis models - UTAHID (Underwater TArget by Highlight Distribution) & M-UTAHID(Modified UTAHID) - of underwater target for active sonar engineering At high frequencies all the echo components that are the specular reflected waves and various elastic scattering wave scan be regarded the summation of individual echo from some equivalent scattering centers, so the underwater target is characterized by highlights distributed in spatial target structure. Proposed models are compared with characteristics of random distributed model & equivalent interval highlight model, and analyzed target strength, echo-elongation effect, target time spread loss and so on. Thus these can be efficiently used in various real systems related to underwater target echo-signal synthesis on active sonar and acoustic countermeasure.

• Journal of the Korea Society for Simulation
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• v.23 no.4
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• pp.181-188
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• 2014

Heterogeneous physical systems and computational devices are incorporated on a large-scale in a CPS (cyber-physical system) environment. Simulations can be useful for the reliable behaviors of CPSs. Time synchronization is one of major technical issues for the simulations. In the CPS, distributed systems control themselves by interacting with each other during runtime. When some simulation models have high complexity, wrong control commands as well as incorrect data can be exchanged due to the time error. We propose a time synchronization algorithm for the hybrid model that has characteristics of both continuous time systems and discrete event systems. In addition, we develop a CPS simulator based on our algorithm. For the verification of the algorithm and the execution of the simulator, we develop an example hybrid model and simulate considering user controls as well as interactions among the distributed systems.

• Journal of Korea Multimedia Society
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• v.3 no.5
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• pp.506-515
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• 2000

In this paper a web-based real-time education system, which is able to support education through multimedia, is suggested for the expansion of learner's creative ability in the school. This system is designed so that it can support three things: 1) a real time interaction between interaction between instructors and learners, 2) individual learning through such an interaction, and 3) a coercive distribution of display by instructions for preventing the deviation of learners from learning. Also, the system, which UML is applied to, makers efficient interaction possible through the module for the real-time exchange and management of messages even in the multi-user environment. Through this system, not only the simulation by learners can be made for experiments and practices, but also questions and respondence can be supported on the procedure of experiments and the analysis of their results. This system is bulit on constructivism, and aimed at helping the learning progress and knowledge formation of learners.

• Proceedings of the Korea Society for Simulation Conference
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• 1998.03a
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• pp.33-36
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• 1998

시뮬레이션을 이용한 위게임 체계는 실 기동훈련체계를 효과적으로 보완할 수 있는 육군의 부대훈련체계로서 정착되어 있으며, 이를 위하여 실시간에 전장상황을 처리하고 필요시 진행시간 조정, 상황 재현 등의 임의 통제가 가능한 워게임 모델 개발에 대한 요구가 증가하고 있다. 본 연구에서는 다기능, 다제대 동시훈련이 가능한 분산형 워게임 시뮬레이션 모델 개발을 수행한 내용으로, 연대전투모델에서 분산 처리가 가능한 분야를 도출하고, 이를 실시간 처리 기준에 맞도록 모델링에서 분산 처리가 가능한 분야를 도출하고, 이를 실시간 처리 기준에 맞도록 모델링에 반영하였다. 분산 워게임 모델 구현을 위하여 실시간 분산객체 기술의 한 분야인 TMO(Time Triggered Message Triggered Object) 모델을 기반으로 nstks처리 모델을 설계하였고, 논문에서는 현재까지 분산형 워게임 모델 개발에 대한 연구 결과와 향후 연구 방향을 제시하고자 한다.

• Journal of the Korean Association of Geographic Information Studies
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• v.11 no.3
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• pp.52-67
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• 2008

Recently, frequent occurrence of flash floods caused by climactic change has necessitated prompt and quantitative prediction of precipitation. In particular, the usability of rainfall radar that can carry out real-time observation and prediction of precipitation behavior has increased. Moreover, the use of distributed hydrological model that enables grid level analysis has increased for an efficient use of rainfall radar that provides grid data at 1km resolution. The use of distributed hydrologic model necessitates grid-type spatial data about target basins; to enhance reliability of flood runoff simulation, the use of visible and precise data is necessary. In this paper, physically based $Vflo^{TM}$ model and ModClark, a quasi-distributed hydrological model, were used to carry out flood runoff simulation and comparison of simulation results with data from Imjin River Basin, two-third of which is ungauged. The spatial scope of this study was divided into the whole Imjin River basin area, which includes ungauged area, and Imjin River basin area in South Korea for which relatively accurate and visible data are available. Peak flow and lag time outputs from the two simulations of each region were compared to analyze the impact of uncertainty in topographical parameters and soil parameters on flood runoff simulation and to propose effective methods for flood runoff simulation in ungauged regions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1492-1512
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• 2011

Due to multiple hops, mobility and time-varying channel, supporting delay sensitive real-time traffic in wireless local area network-based (WLAN) mesh networks is a challenging task. In particular for real-time traffic subject to medium access control (MAC) layer control overhead, such as preamble, carrier sense waiting time and the random backoff period, the performance of real-time flows will be degraded greatly. In order to support real-time traffic, an efficient adaptive packet scheduling (APS) scheme is proposed, which aims to improve the system performance by guaranteeing inter-class, intra-class service differentiation and adaptively adjusting the packet length. APS classifies incoming packets by the IEEE 802.11e access class and then queued into a suitable buffer queue. APS employs strict priority service discipline for resource allocation among different service classes to achieve inter-class fairness. By estimating the received signal to interference plus noise ratio (SINR) per bit and current link condition, APS is able to calculate the optimized packet length with bi-dimensional markov MAC model to improve system performance. To achieve the fairness of intra-class, APS also takes maximum tolerable packet delay, transmission requests, and average allocation transmission into consideration to allocate transmission opportunity to the corresponding traffic. Detailed simulation results and comparison with IEEE 802.11e enhanced distributed channel access (EDCA) scheme show that the proposed APS scheme is able to effectively provide inter-class and intra-class differentiate services and improve QoS for real-time traffic in terms of throughput, end-to-end delay, packet loss rate and fairness.

• Journal of the Korea Society for Simulation
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• v.22 no.2
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• pp.53-62
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• 2013

Cloud environment is one in the field of distributed computing and it consists of physical nodes and virtual nodes. In distributed cloud environment, an optimal path search is that each node to perform a search for an optimal path. Synchronization of each node is required for the optimal path search via fast data transmission because of real-time environment. Therefore, a quantization technique is required in order to guarantee QoS(Quality of Service) and search an optimal path. The quantization technique speeds search data transmission of each node. So a main server can transfer data of real-time environment to each node quickly and the nodes can perform to search optimal paths smoothly. In this paper, we propose the quantization technique to solve the search problem. The quantization technique can reduce the total data transmission. In order to experiment the optimal path search system which applied the quantized data transmission, we construct a simulation of cloud environment. Quantization applied cloud environment reduces the amount of data that transferred, and then QoS of an application for the optimal path search problem is guaranteed.

• 한국정보통신설비학회:학술대회논문집
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• 2007.08a
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• pp.136-141
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• 2007

The frequency accuracy and phase alignment is necessary for ensuring the quality of service (QoS) for applications such as voice, real-time video, wireless hand-off, and data over a converged access medium at the telecom network. As telecom networks evolve from circuit to packet switching, proper synchronization algorithm should be meditated for IP networks to achieve performance quality comparable to that of legacy circuit-switched networks. The Time of Packet (ToP) specified in IEEE 1588 is able to synchronize distributed clocks with an accuracy of less than one microsecond in packet networks. But, The ToP can be affected by impairments of a network such as packet delay variation. This paper proposes the efficient method to minimize the expectable delay variation when ToP synchronizes the distributed clocks. The simulation results are presented to demonstrate the improved performance case when the efficient ToP transmit algorithm is applied.