• Journal of applied mathematics & informatics
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• 제26권3_4호
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• pp.721-732
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• 2008

A single server infinite capacity queueing system with Poisson arrival and a general service time distribution along with repeated attempt and server vacation is considered. We made a comprehensive analysis of the system including ergodicity and limiting behaviour. Some operating characteristics are derived and numerical results are presented to test the feasibility of the queueing model.

• 대한산업공학회지
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• 제22권1호
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• pp.95-104
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• 1996

We consider a two-phase queueing system with generalized vacation. Poisson arrivals receive a batch type service in the first phase and individual services in the second phase. The server takes generalized vacation when the system becomes empty. Generalized vacation includes single vacation, multiple vacation, and other types. We consider both gated batch service and exhaustive batch service. This is an extension of the model presented by Selvam and Sivasankaran [6].

• 대한산업공학회지
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• 제24권3호
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• pp.381-386
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• 1998

We frequently encounter stopped random sums when modelling queueing systems. We also notice occasional mishandling of stopped random sums in the literature. The purpose of this note is to prevent further mistakes by identifying and correcting typical mistakes about stopped random sums. As an example model, we use the two-phase M/G/1 queue with multiple vacations.

• Journal of applied mathematics & informatics
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• 제39권5_6호
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• pp.601-616
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• 2021

Retrial queueing models have been studied extensively in the literature. These have many practical applications, especially in service sectors. However, retrial queueing models have their own limitations. Typically, analyzing such models involve level-dependent quasi-birth-and-death processes, and hence some form of a truncation or an approximate method or simulation approach is needed to study in steady-state. Secondly, in general, the customers are not served on a first-come-first-served basis. The latter is the case when a new arrival may find a free server while prior arrivals are waiting in the retrial orbit due to the servers being busy during their arrivals. In this paper, we take a different approach to the study of multi-server retrial queues in which the signals are generated in such a way to provide a reasonably fair treatment to all the customers seeking service. Further, this approach makes the study to be level-independent quasi-birth-and-death process. This approach is different from any considered in the literature. Using matrix-analytic methods we analyze MAP/M/c-type retrial queueing models along with Poisson signals in steady-state. Illustrative numerical examples including a comparison with previously published retrial queues are presented and they show marked improvements in providing a quality of service to the customers.

• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2006년도 추계학술대회
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• pp.493-505
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• 2006

Call center staffing problems have often relied upon queueing models, which are traditionally used to compute average call waiting time. However, the relationship between the in-bound call volume and call abandon rate is not directly explained even with the complex queueing formula while that relationship is a major interest to the hospital due to profitability. In this paper we provide a novel approach for the call center staffing problem by incorporating the relationship between the in-bound call volume and call abandon rate with a nonlinear integer programming, rather than using the traditional queueing model. We perform numerical analyses with actual data obtained from a reservation call center in a hospital.

• Journal of Communications and Networks
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• 제17권3호
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• pp.265-266
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• 2015

In a recent paper [1], the authors investigated the maximum stable throughput region of a network composed of a rechargeable primary user and a secondary user plugged to a reliable power supply. The authors studied the cases of an infinite and a finite energy queue at the primary transmitter. However, the results of the finite case are incorrect. We show that under the proposed energy queue model (a decoupled M/D/1 queueing system with Bernoulli arrivals and the consumption of one energy packet per time slot), the energy queue capacity does not affect the stability region of the network.

• 산업경영시스템학회지
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• 제6권8호
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• pp.93-103
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• 1983

In this paper, we study an optimal service policy of the M/M/2/K queueing system with two types of customers. The incurred costs consist of waiting cost, service cost and incurred costs consist of waiting cost, service cut and changeover cost. The changeover cost occurs when a server who assigned to serve a particular type of customers reassigned to the other types of customers. Two servers serve two types of customers who arrive to the two separate queues. The two types of customers differ in respect of their arrival rate, service rate, waiting cost, and service cost. The servers require a policy, for determining when they should change their service type, which minimizes the long run expected total cost. The policy is obtained by a Markov decision process model that consists of a finite number of states and actions. In order to find the optimal service policy, we define states and actions of the system, compute onestep transition probabilities, and apply to the successive approximations algorithm.

• 산업공학
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• 제8권2호
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• pp.161-169
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• 1995

In this paper, a threshold policy is considered for the Markovian queueing system with server vacations. The threshold policy considered in this paper has the following form: "when the number of customers present in the system increases to N, the server is turned on and serves customers until the system becomes empty". In this paper, we show how the finite capacity or finite population queueing system under a threshold policy can be modeled by the stochastic Petri net. The performance evaluation of the model is carried out using the software called "SPNP". Some examples are also presented in which it is shown that how the optimal threshold policies can be obtained under a linear cost structure.

• 경영과학
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• 제27권1호
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• pp.17-31
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• 2010

Patients entering an emergency care center in a hospital usually visit medical processes in different orders depending on the urgency level and the medical treatments required. We formulate the patient flows among diverse processes in an emergency care center using the Jackson network, which is one of the queueing networks, in order to evaluate the system performances such as the expected queue length and the expected waiting time. We present a case study based on actual data collected from an emergency care center in a hospital, in order to prove the validity of applying the Jackson network model in practice. After assessing the current system performances, we provide operational strategies to reduce waiting at the bottleneck processes and evaluate the impact of those strategies on the entire system.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1994년도 춘계공동학술대회논문집; 창원대학교; 08월 09일 Apr. 1994
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• pp.513-513
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• 1994