• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.921-926
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• 2009

The RPN provides information which includes the risk level and the priority order of maintenance tasks for components. However, if there is no sufficient historical failure data, the historical failure data from other sources can be applied to the target system. And if we use historical data from other sources without any process, there will be concomitant problems according to a discord of each system characteristic, a difference between the present and the date of failure data, etc. In this paper, a new methodology is proposed to model the failure rate as a fuzzy function to resolve these problems. Taking advantage of this result, the RPN can be calculated by using the fuzzy operation. The proposed method is applied to the substation system.

• Journal of Communications and Networks
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• v.7 no.3
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• pp.313-324
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• 2005

The success of the IEEE 802.11 standard has prompted research into efficiency of the different medium access methods and their support for different traffic types. A modified version of the point coordination function (PCF) called modified PCF has been introduced as a way to improve the efficiency over the standard method. It has been shown through a simulation study and a mathematical analysis that channel utilization can be much improved compared to the standard, in case there is no so-called hidden station problem. However, under the hidden station problem, the efficiency of the modified PCF would obviously decrease. In this paper, some enhancements of the modified PCF are introduced. Firstly, we propose a retransmission process to allow frames involved in collisions to be retransmitted. Then, we propose a collision resolution mechanism to reduce the frame collision probability due to the hidden station problem. In addition, we propose a priority scheme to support prioritization for different traffic types such as interactive voice and video, and real-time data traffic in the modified PCF. To prevent the starvation of one low priority traffic, minimum transmission period is also guaranteed to each traffic type via an admission control algorithm. We study the performance of the modified PCF under the hidden station problem and the performance of the modified PCF with priority scheme through simulations. To illustrate the efficiency of the priority scheme, we therefore compare its simulation results with those of some standardized protocols: The distributed coordination function (DCF), the enhanced distributed channel access (EDCA), the PCF, and our previously proposed protocol: The modified PCF without priority scheme. The simulation results show that the increment of delay in the network due to the hidden station problem can be reduced using the proposed collision resolution mechanism. In addition, in a given scenario the modified PCF with priority scheme can provide better quality of service (QoS) support to different traffic types and also support a higher number of data stations than the previous proposals.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.38 no.4
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• pp.59-71
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• 2001

The Current CORBA shows some limitations for its successful deployment in real time system applications. Recently, OMG adopted Real-Time CORBA specification, which is defined as an extension to CORBA. The goal of the Real-Time CORBA is to provide a standard for CORBA ORB implementations that support 'end to end predictability'. In order to support 'end-to-end predictability', Real Time CORBA specifies many components such as priority model, communication protocol configuration, thread management, and etc. Among them, 'priority model' is the most important mechanism for avoiding or bounding priority inversion in CORBA invocations. In this paper, we present our efforts on a design ,and implementation of the Priority Model in Real-Time CORBA specification. The implementation is done as an extension of omniORB2(v.3.0.0), a popular open source non real time ORB. Experiment results demonstrate that our priority model implementation shows better performance and predictability than the non real-time ORB.

• Journal of the Korea Safety Management & Science
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• v.6 no.1
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• pp.147-155
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• 2004

The goal of this paper is to offer a quantitative decision model using Quality Function Deployment(QFD). We consider the factors outsourcing that affect the benefits of the organization and the fifth alternatives that were selected to be considered for outsourcing as customer requirements and technical attributes in QFD. For selecting the outsourcing system, we compute the priority considering interdependencies among alternatives. Thus this paper propose a decision model, which uses the quality function deployment to help practitioners set priority and users in structuring the outsourcing problems.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.101-104
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• 2000

The Current CORBA has many drawbacks to be deployed successfully in real-time system applications. Recently, OMG adopted Real-Time CORBA specification. In this paper. we report our efforts of a design and implementation of Priority Model of Real-Time CORBA spec., which is one of the most important components in Real-Time CORBA spec. The improvement of real-time performances of our implementation is verified by expereiments.

• Journal of applied mathematics & informatics
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• v.26 no.1_2
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• pp.389-393
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• 2008

This paper describes a single-server queue where the server is unavailable during some intervals of time, which is referred to as vacations. The major contribution of this work is to derive general formulas for the additional delay in the vacation models of the single vacations, head of line priority queues with non-preemptive service, and multiple vacations and idle time.

• Journal of applied mathematics & informatics
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• v.5 no.3
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• pp.643-658
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• 1998

In this paper we analyze the performance of a statistical ATM multiplexer with bursty input traffic and two thresholds in the buffer by using queueing model. Two priority levels are considered for source traffic which is modeled by Markov Modulated Poisson Process to represent the bursty characteristics. Service time distributions of two priority sources are assumed to be same and deterministic for ATM environment. The partial buffer sharing scheme with one threshold may experience a sensitive state change around the threshold. But the proposed multiplexer with two thresholds avoids this hysterical phenominon to improve the system operation.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.9
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• pp.10-17
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• 1994

In this paper, a priority schedling and a flow control algorithm with hysteresis effect are proposed for high-speed networks. A mathematical model for the flow control is proposed and a cell transition probability from this model is found. And the performance of the proposed algorithm is analyzed by a computer simulation. According to the simulation results, it can be shown that the priority scheduling and the flow control with hysteresis effect get the cell loss probability 0.061 better and the average delay 100ms better and the average delay 100ms beter than those of single threshold.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.175-176
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• 2007

In this paper, we introduce Satellite Digital Multimedia Broadcasting(S-DMB) system and show the method increasing the channel capacity. To reduce the burden that has to change the existing system, the system has to be offered the Backward-compatibility. This paper show the method using hierarchical 16APSK modulation. And to obtain the reasonable BER performance between existing path(we call high priority) and additional path(we call low priority).

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.4
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• pp.10-24
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• 2006

Performing a survey on the employers of S company that have built an EIP and used it effectively, we examined the priority of success factors that are considered as important ones by managers, general users, and system administrators. Then, we examined whether the priorities are different among the users of EIP according to the job, position, and period of use. Further, we looked into how the past and present EIP system of S company implemented the factors that took the first and the second places in priority for each of the four categories; the category of factors considered at the in of determining whether to build the system, the category of system functions provided in general, the category of functions provided with high priority when the system is used after the building, md the category of factors that make effective use of the system once it is built.