• Journal of Korean Institute of Industrial Engineers
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• v.30 no.4
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• pp.328-337
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• 2004

Tool costs can comprise a significant part of the total operating costs of Flexible Manufacturing Systems. We address the problem of determining the optimal processing times of individual operations and routing mix in FMSs with multiple routes for each part type in order to minimize tool cost, subject to meeting a throughput constraint for each part type. The problem is formulated as a nonlinear program superimposed on a closed queueing network of the FMSs under consideration. Numerical examples reveal the potential of our approach for significant saving in tool costs.

• Journal of Korean Institute of Industrial Engineers
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• v.33 no.4
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• pp.419-423
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• 2007

In this paper, we consider the M/G/1 queueing system with randomized control of T-policy. Whenever the busy period ends, the server is turned off and takes multiple vacations whose interval is fixed time T with probability p or stays on and waits for arriving customers with probability 1-p. We introduce the cost function and determine the optimal combination of (p, T) to minimize the average cost per unit time.

• Journal of the Korean Operations Research and Management Science Society
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• v.16 no.2
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• pp.118-127
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• 1991

In this paper, criteria and algorithms for the optimal service rate in a closed queueing network have been established. The objective is to minimize total cost. It is shown that system throughput is increasing concave over the service rate of a node and cycle time is increasing convex over the set of service times with a single calss of cubsomers. This enables developing an algorithm using a steepest descent method when the cost function for service rate is convex. The efficiency of the algorithm rests on the fact that the steepest descent direction is readily obtained at each iteration from the MVA algorithm. Several numerical examples are presented. The major application of this research is optimization of facility capacity in a manufacturing system.

• Journal of the Korean Operations Research and Management Science Society
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• v.29 no.4
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• pp.1-10
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• 2004

In this paper we study bounds for characteristics of stationary waiting times in (max, +)-linear systems with a Poisson arrival process. which are prevalent in manufacturing systems, kanban systems, cyclic and acyclic fork-and-join type systems, finite or infinite capacity tandem queues with various kinds of blocking, transportation systems, and telecommunication networks, and so on. Recently, some results on series expansion for characteristics, such as higher moments, Laplace transform, and tail probability, of transient and stationary waiting times in a class of (max, +)-linear systems via Taylor series expansions have been studied. In order to overcome the computational complexity in those results, we consider bounds for characteristics of stationary waiting times using valuable stochastic ordering results. Some numerical examples are also provided.

• Journal of the Korean Operations Research and Management Science Society
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• v.29 no.4
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• pp.175-187
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• 2004

We consider the simultaneous selection of part routes for multiple part types in Flexible Manufacturing Systems (FMSs). Using an optimization framework we investigate two alternative route assignment policies. The one, called routing mix policy in the literature, specifies the optimal proportion of each part type to be produced along its alternative routes, assuming that the proportions can be kept during execution. The other one, which we propose and call pallet allocation policy, partitions the pallets assigned to each part type among the routes. The optimization framework used is a nonlinear programming superimposed on a closed queueing network model of an FMS which produces multiple part types with distinct repeated visits to certain workstations. The objective is to maximize the weighted throughput. Our study shows that the simultaneous use of multiple routes leads to reduced bottleneck utilization, improved workload balance, and a significant increase in the FMS's weighted throughput, without any additional capital investments. Based on numerical work, we also conjecture that pallet allocation policy is more robust than routing mix policy, operationally easier to implement, and may yield higher revenues.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1996.11a
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• pp.326-335
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• 1996

In this paper, we quantify the tradeoff between security and performance in secure data communication systems based on the queueing theory, and propose the optimization methods, such as the preprocessing, a message segmentation, compression, integration of compression and encryption and integration of user authentication and access control, which are able to reduce the delay induced by the security mechanisms and protocols. Moreover, we analyze the average delay for the secure data communication systems through the computer simulations, which are modeled by M/M/1, M/E$_2$/1 and M/H$_2$/1 queueing systems, respectively. We consider the DES, RSA digital signature and the combination of IDEA and RSA as security mechanisms for applying security services.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.142-145
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• 1999

In this paper, delay performances are evaluated and compared for three dual-plane switch architectures; dual input queue/dual switching plane (DQDP The terms of DQDP, DQDP-PS and DQDP-GQ were not used in [Turner88], [Lee96] and [Son97]. All these tern are designated in this letter for convenience.) switch, DQDP with plane selector (DQDP-PS) switch and DQDP based on output group queueing (DQDP-OGQ) switch. We show that under random traffic these switches give almost identical delay performances to that of the output queueing switch but under bursty traffic only the DQDP-PS and the DQDP-OGQ switches ran do.

• Proceedings of the KIEE Conference
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• 1987.07b
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• pp.1178-1180
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• 1987

The resequence delay is an important performance measure in a store-and-forword computer network where messages go out of order while traversing logical channel. An analysis of the total delay including resequence delay is presented for M/M/L queueing system with 2 class heterogeneous servers and improvement of delay performance is investigated by simulation.

• The Transactions of the Korea Information Processing Society
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• v.5 no.1
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• pp.33-39
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• 1998

A queueing model for performance evaluation of finite buffered inter-node communication system is proposed in this paper. Each components are modeled as M/M/I/B queues to obtain the steady state probabilities and ar-rival rate and to analyze finite buffer behavior, The overall sysrem is integrated as series queues with blocking. Average delay and throughput are the performance measures studied in this analysis. The analytical results are first validated through simulation. Next, the effect of buffer length is discussed using the proposed model.

• Proceedings of the Korean Statistical Society Conference
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• 2003.10a
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• pp.189-194
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• 2003

We consider an M/G/1 queueing system under P$_{\lambda}^{M}$-service policy. As soon as the workload exceeds threshold ${\lambda}$ > 0, the service rate is increased from 1 to M ${\geq}$ 1 and is kept until the system becomes empty. After assigning several costs, we show that there exists a unique M minimizing the long-run average cost per unit time.