• Journal of Korea Multimedia Society
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• v.12 no.1
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• pp.31-40
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• 2009

Call centers have become the prevalent contact points between companies and their customers. By virtue of recent advances in communication technology, the number and size of call centers have grown dramatically. As a large portion of the operating costs are related to the labor costs, efficient design and workforce staffing are crucial for the economic success of call centers. Therefore it is very important to determine the adequate number of agents. In this context, the workforce staffing level can be modeled as mathematical optimization problem using queueing theory. In this paper, we deal with an approximate analysis of an N-design call center with two finite queues and two types of reneging customers by using the state decomposition method. We also represent some numerical examples and show the impact of the system parameters on the performance measures of the call center.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.5
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• pp.400-404
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• 2009

Native Command Queueing is a technology to maximize throughput of disk system by reordering requests in its command queue. Recent S-ATA 2 standard specifies a protocol for the purpose of dealing with NCQ feature, making most vendors implementing it in their disk devices. However, the new feature, NCQ, may lead to information gap between OS and disk drive. 05 considers that disk will service I/O requests in the order as OS has dispatched. Unfortunately, it isn't true any more since NCQ would simply ignore the policy of OS and reorder the sequence OS has expected. Let us define the term as expectation-discord. Due to the discord, serious performance anomalies or starvation of requests may occur in I/O subsystem. In this paper, we confirm that the expectation-discord actually brings about starvation of requests. We propose a solution to settle it. Our solution is very simple, effective, cheap(not requiring any hardware modification) and portable across various OS. Experimental results show that our solution can balance throughput and response time very well.

• Journal of Fisheries and Marine Sciences Education
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• v.10 no.1
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• pp.1-14
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• 1998

Transportation provides an infrastructure vital to economic growth, and it is also an integral part of production. As a port is regarded as the interface between the maritime transport and domestic transport sectors, it certainly play a key role in any economic development. Ship's delay caused by port congestion has recently has recently attracted attended with the analysis of overall operation in port. In order to analyse complicated port operation which contains large number of variable factors, queueing theory is needed to be adopted, which is applicable to a large scale transportation system in chiding ship's delay in Inchon port in relation to ship's delay problem. The overall findings are as follows ; 1. The stucture of queueing model in this port can be represented as a complex of multi-channel single-phase 2. Ship's arrival and service pattern were Poisson Input Erlangian Service. 3. The suitable formula to calculate the mean delay in this port, namely, $W_q={\frac{{\rho}}{{\lambda}(1-{\rho})}}{\frac{e{\small{N}}({\rho}{\cdot}N)}{D_{N-1}({\rho}{\cdot}N)}}$ Where, ${\lambda}$ : mean arrival rate ${\mu}$ : mean servicing rate N : number of servicing channel ${\rho}$ : utilization rate (l/Nm) $e{\small{N}}$ : the Poisson function $D_{(n-1)}$ : a function of the cumulative Poisson function 4. The utility rate is 95.0 percents in general piers, 75.39 percents in container piers, and watiting time 28.43 hours in general piers, 13.67 hours in container piers, and the length of queue is 6.17 ships in general piers, 0.93 ships in container piers, and the ship turnaround time is 107.03 hours in general piers, 51.93 hours in container piers.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1916-1924
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• 2017

Fossil oil, as the main energy of transportation, is destined to be exhausted. The electrification of transportation is a sustainable solution to the energy crisis, since electric power could be acquired from the inexhaustible sun, wind and water. Among all the problems that hinder the development of Electric Vehicle (EV) industry, charging issue might be the most prominent one. In this paper, the service process of a charging station with Battery Energy Storage System (BESS) is analyzed by means of $Cram{\acute{e}}r$ - Lundberg model which has been intensively utilized in ruin theory. The service quality is proposed in two dimensions: the service efficiency and the service reliability. The arrival rate and State of Charge (SOC) upon arrival are derived from 2009 National Household Travel Survey (NHTS). The simulations are performed to show how the service quality is determined by the system parameters such as the number of servers, the service rate, the initial capacity, the charge rate and the maximum waiting time. At last, the economic analysis of the system is conducted and the best combination of the system parameters are given.

• Journal of the Korean Operations Research and Management Science Society
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• v.27 no.4
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• pp.41-65
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• 2002

We study a multi-component production/inventory system in which individual components are made to meet various demand types. We assume that the demands arrive according to a Poisson process, but there is a fixed probability that a demand requests a particular kit of different components. Each component is produced by a flow line with several stations in which the processing times of each station follow a two-stage Coxian distribution. The production of each component is operated by an independent base-stock policy with blocking. We assume that the time needed to assemble final products follows a general distribution and the capacity of an assembling facility is sufficiently large. The objective of this study is to obtain key performance measures such as the distribution of the number of each orders for each final product and the mean time of fulfilling a customer order. The basic principle of the proposed approximation method is to decompose the original system into a set of subsystems, each subsystem being associated with a flow line. Each subsystem is analyzed in isolation using a Marie's method. An iterative procedure is then used to determine the unknown parameters of each subsystem. Numerical results show that the accuracy of the approximation method is acceptable.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.92-96
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• 2000

In this paper, we propose a call admission control(CAC) scheme fer the mixed voice/data DS-CDMA systems and analyze the Er-lang capacity under the proposed CAC scheme. Voice and data traffics require different system resources based oil their Quality of Service(QoS) requirements. In the proposed CAC scheme, some system resources are reserved exclusively for handoff calls to have high priority Over new calls. Additionally the queueing of both new and handoff data traffics that are not sensitive to delay is allowed. Ar a performance measure for the suggested CAC scheme. Erlang capacity is utilized. For the performance analysis, a four-dimensional Markov chain model is developed. Erlang capacity of a practical IS-95B type system depicts, and optimum values of system parameters such as the number of reservation channels and queue lengths are found with respect to Erlang capacity. Finally, it is observed that Erlang capacity is improved more than two times by properly selecting the system parameters with the proposed CAC scheme.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.7
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• pp.1393-1398
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• 2003

In this paper, we propose a new switch architecture with one schedule at k-time slots, which k means the allocated time slots for each schedule. A conventional switch system uses a single time slot per each schedule but the proposed switch system uses multiple time slots per each schedule. Both the conventional switch md the proposed switch have same throughput but our switch system occupies multiple cell time slots per each schedule and hence can be implemented in scheduler of simple circuitry compared to the conventional switch. The proposed scheduling method for switch system will be applicable in switch system with high-speed data link rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.11
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• pp.1785-1796
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• 1993

Thanks to the data processing facilities of modern digital computers, the performances of radar has been promoted greatly as one of the main components of command and control systems along with the computer communications. In this study, radar data integrating and processing systems were designed for the data processing of various information from many kinds of radar in a single data processing system. The performance of the data integrating system was analyzed by applying queueing theory. A radar data integrating network was designed for synchronous relational operations among the information processing systems and the transmission characteristics were also analysed by specific models for each system. The designed data integrating systems can be divided into a simplex type and a distributed multiplex type.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.3
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• pp.434-441
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• 1994

In this paper, performance of MAP management system traffic is analyzed, to realize the network management function in automated manufacturing network mini-MAP. The network management system, which controls and supervises the network resources in the communication network, is the function that is necessarily required in this network. Since the real time response must be required in the Mini-MAP network, the delay performance of the network needs to be analyzed. By means of both analytical method and simulation for cyclic queueing model, the delay time distributions due to the increasement of transmission data are obtained in the implemented management network where SLAM II package is used for simulation. In addition, the parameters of the management function affecting the transmission delay are considered so that these parameters can be used to implement network management system.

• Journal of the Korean Operations Research and Management Science Society
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• v.23 no.3
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• pp.135-151
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• 1998

The demand of large capacity in coming cellular systems makes inevitable the deployment of small cells, rendering more frequent handoff occurrences of calls than in the conventional system. The key issue is then how effectively to reduce the chance of unsuccessful handoffs, since the handoff failure is less desirable than that of a new call attempt. In this study, we consider the control policies which give priority to handoff calls by limiting channel assignment for the originating new calls, and allow queueing the new calls which are rejected at their first attempts. On this system. we propose the problem of finding an optimal call control strategy which optimizes the objective function value, while satisfying the requirements on the handoff/new call blocking probabilities and the new call delay. The objective function takes the most general form to include such well-known performance measures as the weighted average carried traffic and the handoff call blocking probability. The problem is formulated into two different linear programming (LP) models. One is based on the direct employment of steady state equations, and the other uses the theory of semi-Markov decision process. Two LP formulations are competitive each other, having its own strength in the numbers of variables and constraints. Extensive experiments are also conducted to show which call control strategy is optimal under various system environments having different objective functions and traffic patterns.