• International Journal of Reliability and Applications
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• v.11 no.2
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• pp.89-106
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• 2010

This paper deals with the reliability and availability characteristics of three different series system configurations with warm standby components and a repairable service station. The failure time of the primary and warm standby are assumed to be exponentially distributed with parameters ${\lambda}$ and ${\alpha}$ respectively. The repair time distribution of each server is also exponentially distributed with parameter ${\mu}$. The breakdown time and the repair time of the service station are also assumed exponentially distributed with parameters ${\gamma}$ and ${\beta}$ respectively. We derive the reliability dependent on time, availability dependent on time, the mean time to failure, $MTTF_i$, and the steady-state availability $A_i$(${\infty}$) for three configurations and perform comparisons. Comparisons are made for specific values of distribution parameters and of the cost of the components. The three configurations are ranked based on: $MTTF_i$, $A_i$(${\infty}$), and $C_i/B_i$ where $B_i$ is either $MTTF_i$ or $A_i$(${\infty}$).

• The KIPS Transactions:PartB
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• v.15B no.5
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• pp.465-476
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• 2008

To provide autonomous and dynamic services for users in a ubiquitous environment where heterogeneity, mobility and variability are main characteristics, an efficient service description/structuring mechanism and a service composition method are essential. Service composition can consider context in real-time and compose appropriate services. In this research, we propose a mechanism for extracting services from a specific domain and structuring them into hierarchical service ontology. Each service is described using the proposed service specification. Based on this service ontology, users can represent their goals using various abstraction levels of services, and then our service overloading method enables to invoke the most appropriate service at the execution time. Moreover, we present a method which can discovery an alternative service by referencing the service ontology, when the requested service is not available. The experimental result shows that our service ontology could improve the success probability of users' goals and reduce service binding time compare to using just an unstructured list of services.

• KIPS Transactions on Software and Data Engineering
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• v.1 no.3
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• pp.149-158
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• 2012

As service-oriented software is considered as one of solutions to fulfill the users' needs in internet service environment, it has been increased the demands of reliable service development by the composition of internet services. However a critical issue in the service development approach is to satisfy the performance requirement as well as the functional correctness for the developing services, because impatient user multiply clicks the request-button of service without a short waiting. This paper proposes a framework to examine the performance of composite service. Our testing framework provides the data of service response time to service developer by measuring the service execution time. We develope an Aspect-based timer service, and weave the service with existing services to measure the execution time. Additionally, we perform some experiments to confirm the usefulness of performance test for composite service. This framework can support to develop a good performance service by substitution of the dragging service with another new service that will be a component of composite service.

• Journal of Service Research and Studies
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• v.10 no.3
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• pp.55-66
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• 2020

This study was attempted to demonstrate the service performance of non-face-to-face real-time video lecture service conducted in the coronavirus crisis in early 2020. Lecture service is divided into service production and service delivery from a service system perspective, and its role of lecture service system and the relationship between lecture service benefits and service satisfaction perceived by learners is demonstrated. In order to demonstrate this structural impact relationship, the result of analysis through a questionnaire survey on a total of 268 undergraduate students at G University, showed that the role and level of the non-face-to-face real-time video lecture service system affects the service convenience and service satisfaction. In the additional analysis, the learning orientation learners group perceived the service system level or role in the lecture service and the service benefit itself higher than the relationship orientation learners group. In the past, when a face-to-face class was conducted, learners group who attended a lot of extra curriculum activities perceived the benefits of coronavirus prevention lower than those of a group that did not. In this way, it is necessary to supplement the lecture service system by identifying the role expectation in the lecture service for the high relationship orientation group and the preferring extra curriculum activity group after detail research.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.04a
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• pp.477-480
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• 1996

The main objective of this research is to develop the optimal control method for a Distribution Center - multi Branch inventory distribution system. With the continuous review policy, the distribution center places an order for specific order quantity to an outside supplier, and the order quantity is replenished after a certain lead time. Also, each branch places an order for particular order quantity to the distribution center to satisfy the customer demands, and receives the replenishment after a lead time. When an out of stock condition occurs during an order cycle, a backorder is placed to the upper level to fill the unfilled demands. With these situation, variable demand and variable lead time are used for better industrial practice. Futher, actual lead times with a generic lead time distribution are used in developing the control model. Under the actual lead time model, the customer service measures actually attained for the distribution center and each branch are explained as the effective customer service measures. Thus, throughout the optimal control (using computer search procedures), we can set the desired service levels for the distribution center and each branch to produce the effective service level for each branch which is consistent with the goal level of service for each branch. At the same time, the entire distribution system keeps minimum inventories.

• Journal of Korean Institute of Industrial Engineers
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• v.27 no.1
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• pp.18-24
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• 2001

This paper presents a model and a heuristic algorithm for the Traveling Salesman Problem with Time Windows(TSPTW). The main difference of our model compared with the previous ones lies in that the time windows we are concerned are more flexible and realistic than the previous ones. In the typical TSPTW, the service at a node must begin within the time grid called the time window that is defined by the earliest and the latest time to start the service at each node. But, in real business practice, a lateness cost is usually penalized rather than the service is prohibited at all when a vehicle arrives after the latest time. Considering this situation, we develop a model with a new time window that allows an arrival after the latest time and penalizes the late arrival by charging a lateness cost. A two-phased heuristic algorithm is proposed for the model and is extensively tested to verify the accuracy and efficiency of the algorithm.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1699-1706
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• 2011

This study analyzed the level of service on passenger transfer between metro and bus based on transit smart card data obtained in 2010. In order to evaluate the level of service on transfer, we defined the service level specially on transfer time at metro stations. The data of passenger transfer time were used in cluster analysis to classify the service level from A to F. The results show that the average transfer time from metro to bus was 6.45 minutes. The number of stations with level of service A(approximately less than 7 minutes) and B(less than 16minutes) were found to be 215 and 227stations respectively. Also, the number of stations with the level of service C and D (greater than 20 minutes for transfer) were found to be 6 stations where any type of improvement on transfer facilities is required.

• Journal of applied mathematics & informatics
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• v.31 no.1_2
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• pp.147-154
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• 2013

We analyze queueing model with priority scheduling by supplementary variable method. Customers are classified into two types (type-1 and type-2 ) according to their characteristics. Customers of each type arrive by independent Poisson processes, and all customers regardless of type have same general service time. The service order of each type is determined by the queue length of type-1 buffer. If the queue length of type-1 customer exceeds a threshold L, the service priority is given to the type-1 customer. Otherwise, the service priority is given to type-2 customer. Method of supplementary variable by remaining service time gives us information for queue length of two buffers. That is, we derive the differential difference equations for our queueing system. We obtain joint probability generating function for two queue lengths and the remaining service time. Also, the mean queue length of each buffer is derived.

• Proceedings of the Korea Inteligent Information System Society Conference
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• 2001.01a
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• pp.198-201
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• 2001

Recently the wireless-internet has been spreading extensively. People are spending a large part of their time gaining access to information using a mobile device. With the rapid growth of on-line Electronic Commerce, the use of mobile devices creates a new paradigm that provides users with location-independent real time service. Although this new paradigm does have some advantages, limited process speed, low bandwidth, the low battery capacity of mobile devices, and a high rate of wireless network errors causes many overhead expenses during service time with the server. In this paper, we suggest an autonomous service delivery system, which provides mobile agent capability to users that cannot maintain a connection. We have developed the system based on java mobile agent technology. Using this system, we can provide more effective service to users when the user is sending requirements for service through a mobile device that has limited resources. Furthermore we can manage the contact server dynamically when new services are added.

• Journal of the Korea Society of Computer and Information
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• v.21 no.10
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• pp.69-76
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• 2016

In this paper, we propose a real-time remote logging model for development of android applications using LBS(Location based Service). The model has two major parts: Mobile Log Management Service and Remote Log Server. Mobile Log Management Service consists of the log collector and the remote log manager. The log collector is an aspect of AOP which can collect logs from the target application without modifications of source codes. The remote log manager has a background service component so that it can receive logs whenever the log collector captures logs from the target application. Remote Log Server communicates with Mobile Log Management Service by socket interface. Therefore, Remote Log Server can show logs in real-time. To validate the efficiency of the proposed model, we show a case study, and compare the model with other models.