• Industrial Engineering and Management Systems
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• 제12권3호
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• pp.281-287
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• 2013

In this paper, we introduce a roots method that uses the roots inside the unit circle of the associated characteristics equation to evaluate the steady-state system-length distribution at three epochs (pre-arrival, arbitrary, and post-departure) and sojourn-time distribution in GI/PH/1 queueing model. It is very important for an air base to inspect airplane oil because low-quality oil leads to drop or breakdown of an airplane. Since airplane oil inspection is composed of several inspection steps, it sometimes causes train congestion and delay of inventory replenishments. We analyzed interarrival time and inspection (service) time of oil supply from the actual data which is given from one of the ROKAF's (Republic of Korea Air Force) bases. We found that interarrival time of oil follows a normal distribution with a small deviation, and the service time follows phase-type distribution, which was first introduced by Neuts to deal with the shortfalls of exponential distributions. Finally, we applied the GI/PH/1 queueing model to the oil train congestion problem and analyzed the distributions of the number of customers (oil trains) in the queue and their mean sojourn-time using the roots method suggested by Chaudhry for the model GI/C-MSP/1.

• 한국건설관리학회:학술대회논문집
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• 한국건설관리학회 2008년도 정기학술발표대회 논문집
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• pp.628-633
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• 2008

건축물에 있어서 고층화 대형화의 변화는 인력과 자재의 양중부하를 증가시키는 동시에 수직양중작업의 이동거리를 증가시킨다. 이로 인해 고층으로의 운반정체는 물론 대기상태증가로 인한 생산성 감소의 문제를 발생시킨다. 이에 고층 건물 공사초기의 양중계획은 건설현장의 특성을 면밀히 고려하고 효과적으로 계획수립에 반영될 필요성이 있다. 하지만 현재 건설현장에서 가설리프트 계획수립은 사이클 주기(Cycle Time)를 바탕으로 한 단순계산식을 사용하고 있다. 이 방법은 쉽고 간단하지만, 복잡하고 유기적인 현장의 현실을 제대로 고려하지 못한다는 한계가 있다. 따라서 본 연구에서는 이러한 한계점을 극복하기 위한 방안으로, 확률적 대기행렬의 큐잉이론(Queueing Theory)을 이용한 시뮬레이션모델의 적용 가능성에 대해 알아보고자 한다.

• 한국통신학회논문지
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• 제30권2A호
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• pp.98-106
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• 2005

본 논문에서는 MAC 계층 이하에 존재하는 링크 계층 재전송 기법과 잘 부합할 수 있는 새로운 무선 패킷 스케줄링 알고리즘인 WFQ-R (Wireless Fair Queueing with Retransmission) 알고리즘을 제안한다. WFQ-R 알고리즘에서 링크 계층 재전송에 의해 사용된 자원은 재전송을 수행한 플로우(flow)가 다른 플로우들에게 미리 차용한 자원으로 취급한다. 즉 MAC 계층 이하의 재전송 과정에서 패킷 스케줄러의 허락 없이 사용되어진 자원을 재전송을 수행한 플로우에게 책임 지움으로써 WFQ-R 알고리즘은 무선 공평성(fairness)을 획득할 수 있게 된다. 본 논문에서는 실험을 통하여 WFQ-R 알고리즘기 공평성을 유지함과 동시에 시스템 성능을 최대화 함을 보인다. 또 플로우 구분성(seperation)과 보상성(compensation)도 획득할 수 있음도 보인다.

• 경영과학
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• 제28권3호
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• pp.15-29
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• 2011

In this paper, we consider a system working at both primary service and secondary service. A server can switch between the primary service and the secondary service or it can be assigned to secondary service as a dedicated server. A service policy is characterized by the number of servers dedicated to the secondary service and a rule for switching the remaining servers between two services. The primary service system is modelled as a Markovian queueing system and the throughput is a function of the number of servers, buffer capacity, and service policy. And the secondary service system has a service level requirement strategically determined to perform the service assigned. There is a revenue obtained from throughput and costs due to servers and buffers. We study the problem of simultaneously determining the optimal total number of servers, buffers, and service policy to maximize profit of the system subject to both an expected customer waiting time constraint of the primary service and a service level constraint of the secondary service and develop an algorithm which can be successfully applied with the small number of computations.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2002년도 춘계 학술발표회 논문집
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• pp.61-66
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• 2002

We consider a generalized N-policy for an M/M/1 queueing system. The idle server starts to work with ordinary service rate when a customer arrives. If the number of customers in the system reaches N, the service rate gets faster and continues until the system becomes empty. Otherwise, the server finishes the busy period with ordinary service rate. We obtain the limiting distribution of the number of customers in the system. After assigning various operating costs to the system, we show that there exists a unique fast service rate minimizing the long-run average cost per unit time.

• 대한산업공학회지
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• 제42권1호
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• pp.30-37
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• 2016

A multi-server queueing system with an infinite buffer and impatient customers is analyzed. The system operates in the finite state Markovian random environment. The number of available servers, the parameters of the batch Markovian arrival process, the rate of customers' service, and the impatience intensity depend on the current state of the random environment and immediately change their values at the moments of jumps of the random environment. Dynamics of the system is described by the multi-dimensional asymptotically quasi-Toeplitz Markov chain. The ergodicity condition is derived. The main performance measures of the system are calculated. Numerical results are presented.

• ETRI Journal
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• 제25권4호
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• pp.238-246
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• 2003

This paper introduces the modeling and analysis of a discrete-time, two-phase queueing system for both exhaustive batch service and gated batch service. Packets arrive at the system according to a Bernoulli process and receive batch service in the first phase and individual services in the second phase. We derive the probability generating function (PGF) of the system size and show that it is decomposed into two PGFs, one of which is the PGF of the system size in the standard discrete-time Geo/G/1 queue without vacations. We also present the PGF of the sojourn time. Based on these PGFs, we present useful performance measures, such as the mean number of packets in the system and the mean sojourn time of a packet.

• 산업경영시스템학회지
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• 제28권4호
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• pp.134-141
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• 2005

Due to the complexity and stochastic nature of automated warehousing system, items are usually queued up at I/O point. We introduce a storage/retrieval policy : dual-command. We present quick approximations to queueing phenomena under these policies. It is assumed that the storage and retrieval arrival pattern follow the same poisson process. We also assumed that storage queue and retrieval queue being operated separately. The approximation attempts are performed under the proposed storage/retrieval policies after we derive S/R machine travel time distributions.

• Journal of applied mathematics & informatics
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• 제6권2호
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• pp.553-568
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• 1999

This paper is of concern to queueing analysis of the dynamic rate leaky bucket(LB) scheme in which the token generation interval changes according to the buffer state at a token generation epoch. Cell arrivals are assumed to follow a Markovian arrival process (MAP) which is weakly dense in the class of the stationary point processes. By using the embedded Markov chain method we obtain the probability distribution of the system state at a token generation epoch and an arbitrary time. Some simple numerical examples also are provided to show the effects of the proposed LB scheme.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제17권2호
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• pp.103-113
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• 2013

We analyze the queueing model for leaky bucket (LB) scheme with dynamic arrivals and token rates. In other words, in our LB scheme the arrivals and token rates are changed according to the buffer occupancy. In telecommunication networks, the LB scheme has been used as a policing function to prevent congestion. By considering bursty and correlated properties of input traffic, the arrivals are assumed to follow a Markov-modulated Poisson process (MMPP). We derive the distribution of system state, and obtain the loss probability and the mean waiting time. The analysis is done by using the embedded Markov chain and supplementary variable method. We also present some numerical examples to show the effect of our proposed model.