• Journal of the Korean Operations Research and Management Science Society
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• v.24 no.4
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• pp.111-122
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• 1999

In this paper, we consider a queueing network model. where the population constraint within each subnetwork is controlled by a semaphore queue. The total number of customers that may be present in the subnetwork can not exceed a given value. Each node has a constant service time and the arrival process to the queueing network is an arbitrary distribution. A major characteristics of this model is that the lower layer flow is halted by the state of higher layer. We present some properties that the inter-change of nodes does not make any difference to customer's waiting time in the queueing network under a certain condition. The queueing network can be transformed into a simplified queueing network. A dramatic simplification of the queueing network is shown. It is interesting to see how the simplification developed for sliding window flow control, can be applied to multi-layered queueing network.

• Journal of the Korean Operations Research and Management Science Society
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• v.33 no.2
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• pp.115-135
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• 2008

An interesting problem in capacitated supply chains is how to guarantee customer service levels with limited resources. One of the common approaches to solve the problem is differentiating service depending on customer classes. High-priority customers receive a better service at the cost of low-priority customers' service level. One of common criteria to determine a customer's priority in practice is whether he has made a reservation before arrival or not. Customers with a reservation usually receive service based on the time the reservation was made. We examine the effect this advance information of customer arrival has on customer service levels. We show the trade-offs between the leadtime and other system characteristics such as the proportion of high-priority customers. when the service level is high. We also suggest how to differentiate service using the asymptotic ratio of the service levels for both types of customers.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2007.11a
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• pp.325-329
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• 2007

The mobile and multimedia service on wireless network have been leaded from the improvement of telecommunication techniques. A typical multimedia service, a video transmission usually requires larger bandwidth than voice transmission. Many channel allocation algorithms for Orthogonal Frequency Division Multiple Access (OFBMA) to use resources more efficiently, Previous channel allocation algorithms have developed with an assumption that the data traffic is constant bit rate (CBR). However, existing algorithms are not suitable to video traffic because it usually generates a variable bit rate (VBR) traffic. In this paper, we proposed a new channel allocation algorithm called a queue-based channel allocation. it is more suitable to transmit the video traffics. Also, a problem are notified in case of realtime generated video traffic and a corresponding heuristic solution was proposed.

• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.3
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• pp.99-111
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• 1997

We consider a production system with post-operation and early set-up. As soon as there are no more units(raw materials) to process and the machine becomes idle, it undergoes a post-operation. After the post operation, if the number of waiting units is greater than or equal to m, it begins a set-up. After the set-up, if the number of units is greater than or equal to N($\geq$m), it begins to process the units. We first analyze the system by employing the decomposition property of the vacation queue. We, then, propose an algorithm that finds the optimal threshold values ($m^*$, $N^*$). Finally we present some numerical examples and interprete the system behavior.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.04a
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• pp.435-444
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• 1995

We propose a new approach to the calculation of the exact cells loss probability in a shared buffer ATM multiplexer, which is loaded with homogeneous discrete-time ON-OFF sources. Renewal cycles are identified in regard to the state of input sources and the buffer state on each renewal circle is modelled as a K(shared buffer size)-state Markov chain. We also analyze the behavior of queue build-up at the shared buffer whose distribution together with the steady-state probabilities of the Markov chain leads to the exact cell loss probability. Our approach to obtaining the exact cell loss probability seems to be more efficient than most of other existing ones since our underlying Markov chain has less number of states.

• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.4
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• pp.1-16
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• 1997

The cell loss probability recommended in the B-ISDN is in the range $10^{-8}~10^{-12}$. When a simulation technique is used to analyze the performance of the ATM node, an enormous amount of computer processing time is required. In this study, we derive an importance sampling simulation technique that can be used to evaluate the performance of the ATM node very quickly, that is, the probability that the queue size at the ATM node reaches some large value N. The simulation results show that the backlog probability obtianed by the importance saimpling simulation is very close to that obtained by the ordinary simulation and the computer time can be reduced drastically by the importance sampling simulation.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.09a
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• pp.113-118
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• 1995

본 연구는 폐쇄형 대기행렬망(CQN:Closed Network of Queue)으로 표시되는 FMS 시스템의 최적 성능을 산정하는 방법과 각 작업장의 작업 부하 (Workload)를 최적화하기 위한 방법에 관한 연구이다. FMS 생산 시스템의 성능 (Performance)을 기존의 생산률(Production Rate)외에 기대생산률 (Expected Production Rate), 평균 대기작업량(Mean Queueue Length), 및 기대 투자이용률(Expected Investment Utilization Rate)과 이들 각각의 분산 (Variance)들을 고려하였다. 이러한 성과측정 문제를 수리 모델링하고 이를 이용하여 각 작업장에서의 가공 장비의 그룹(Machine Group)별 최적 작업배 분(Workload) 조건을 보였다. 또한 위의 과정을 최근의 FMS 전용 Simulator인 FACTOR/AIM을 이용한 분석 결과와 비교하여 보였다.

• Journal of the Korean Operations Research and Management Science Society
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• v.11 no.1
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• pp.7-11
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• 1986

Throughout this paper we analyze the system at output point t of two stage cyclic queueing model. Our main result characterize the stochastic process (X$^{o}$ , T$^{o}$ ), the system at output point, as a Markov renewal process. The subsequent lemma exhibits the semi-Markov kernel of (X$^{o}$ , T$^{o}$ ) with state dependent feedback, the possibility of a reducible state space arises. A simple necessary and sufficient condition for the irreducibility of (X$^{o}$ , T$^{o}$ was determinded. This irreducibility implied that (X$^{o}$ , T$^{o}$ ) was aperiodic.

• Journal of Korean Society of Transportation
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• v.8 no.1
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• pp.5-15
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• 1990

As a result of the lack of methodology for the determination of navigational channel capacity and the consequence lack of effective management of traffic, navigational channels are often grossly underutilized or highly congested. The traditional rule of first-come-first-served admission of vessels to channels is not efficient as it assumes equal time intervals between entrance of consecutive vessels. A new vessel traffic management system is developed in this research and methodologies to measure the improvement in the channel capacity are developed. Methodology to measure the channel performances for three queue disciplines are developed. The effects of changes in major factors on the channel capacity model such as channel length, fleet mix and arrival rate, as well as changes in strategy are analyzed. Under given channel conditions, best strategy are recommended. Also, a method for effective stochastic channel capacity simulation was developed. The results of analysis and as ertions are compared with the results of simulation runs to prove their applicability.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.892-895
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• 2002

We propose new buffer management scheme for GFR service through FIFO queuing discipline. Proposed scheme can provide minimum bandwidth guarantees for GFR VCs as well as improve the fairness among the competing GFR VCs on a single FIFO queue. From simulation results, we demonstrate the proposed scheme fulfills the requirements of GFR service as well as improves the TCP throughput.