• Journal of Korean Institute of Industrial Engineers
• /
• v.16 no.1
• /
• pp.107-114
• /
• 1990

A queueing system with compound Poisson arrival and server vacation is analyzed by including supplementary variables. We consider a vacation system in which the server leaves for a vacation as soon as the system empties. When he returns, if no customer is waiting for service, he waits until a group of customers arrive and then begins to serve. We obtain the system size distribution and the waiting time distribution. Additional performance measures will be also considered.

• Communications for Statistical Applications and Methods
• /
• v.24 no.3
• /
• pp.193-209
• /
• 2017

The power Lindley distribution with some of its properties is considered in this article. Maximum likelihood, least squares, maximum product spacings, and Bayes estimators are proposed to estimate all the unknown parameters of the power Lindley distribution. Lindley's approximation and Markov chain Monte Carlo techniques are utilized for Bayesian calculations since posterior distribution cannot be reduced to standard distribution. The performances of the proposed estimators are compared based on simulated samples. The waiting times of research articles to be accepted in statistical journals are fitted to the power Lindley distribution with other competing distributions. Chi-square statistic, Kolmogorov-Smirnov statistic, Akaike information criterion and Bayesian information criterion are used to access goodness-of-fit. It was found that the power Lindley distribution gives a better fit for the data than other distributions.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 1993.04a
• /
• pp.229-229
• /
• 1993

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 2005.05a
• /
• pp.1129-1132
• /
• 2005

Based on a discrete-time version of the distributional Little's law, we present a simple computational procedure to obtain the queue-length distribution of the discrete-time GI/G/1 queue from its waiting-time distribution that is available by various existing methods. We also discuss our numerical experience and address a couple of remarks on possible extensions of the procedure.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.19 no.1
• /
• pp.85-98
• /
• 1994

The distribution of random sum of i. i. d. exponential random variables is called GHP (Generalized Phase-Type) distribution. The class of GPH distributions is large enough to include PH (Phase-Type) distributions and has several properties which can be applied conveniently for computational purposes. In this paper, we show that any distribution difined on R$^{+}$ can be app-roximated by the GPH distribution and demonstrate the accuracy of the approximation through various numerical examples. Also, we introduce an efficient way to compute the delay and waiting various numerical examples. Also, we introduce an efficient way to compute the delay and waiting time distributions of the GPH/GPH/1 queueing system which can be used as an approximation model for the GI/G/1 system, and validate its accuracy through numerical examples. The theoretical and experimental results of this paper help us accept the usefulness of the approximations based on GPH distribution.n.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.19 no.3
• /
• pp.235-241
• /
• 1994

We consider a B/G/1 queueing with vacations, where the server closes the gate when it begins a vacation. In this system, customers arrive according to a Bernoulli process. The service time and the vacation time follow discrete distributions. We obtain the distribution of the number of customers at a random point in time, and in turn, the distribution of the residence time (queueing time + service time) for a customer. It is observed that solutions for our discret time B/G/1 gated vacation model are analogous to those for the continuous time M/G/1 gated vacation model.

• Korean Journal of Community Nutrition
• /
• v.22 no.2
• /
• pp.127-135
• /
• 2017

Objectives: This study was conducted to examine the satisfaction of school cafeterias among the surveyed group at two middle schools located in Seoul. Methods: 574 out of 600 middle school students in Seoul (95.7%) completed the study. Results: Satisfaction rate of school meals was significantly higher among girls (73.2%) compared to boys (45.1%). The reasons for satisfaction factors of school meals were with the taste of school meals (55.1%), menu (19.3%), nutrition (14.2%), and food hygiene safety (7.0%). Students who had a double-income family, well-educated mother and higher happiness in their life reported a higher satisfaction with school meals. Both boys and girls who consumed milk frequently showed significantly higher satisfaction with school meals. Factors that were related to satisfaction of school meals were food temperature, the amount of food (especially among boys). Variety in the menu and food distribution speed were less related to the satisfaction of meals. In the case of girls, waiting time, food distribution speed were more important to them while the kindness of school staff was a less important factor. Improvements that were needed to increase the satisfaction for the school lunch meals, from the most important to least important were as follows: variety of meals (36.6%), food distribution speed waiting time (24.6%), taste of food (15.7%), amount of food (7.7%), hygienic management (5.1%), food quality (4.7%), kindness (3.0%), temperature of the food (2.8%). Students preferred to broadcast on campus and cooking practice for the dietary education. Conclusions: To improve school meal satisfaction, it is necessary for food distribution facilities to make improvements with regard to variety of meals and reduced waiting time.

• Proceedings of the IEEK Conference
• /
• 2000.07a
• /
• pp.322-325
• /
• 2000

In a batch scheduling policy being different from real video system, the requests are not served immediately due to grouping user's requests upon every scheduling points. Such waiting delays by inefficient managements makes an unfair service to users and increases the possibility of higher reneging rates. This paper proposes an adaptive batch scheduling scheme which reduces the average waiting time of user’s requests and reduces the starvation problem for requesters of less popular movies. The proposed scheme selects dynamically multiple videos in given intervals based on the service patterns which reflect the popularity distribution and resource utilizations. Experimental simulation shows that proposed scheme improves about 20-30 percent of average waiting time and reduces significantly the starving requesters comparing with those of conventional methods such as FCFS and MQL.

• Journal of Korean Institute of Industrial Engineers
• /
• v.28 no.4
• /
• pp.390-396
• /
• 2002

We present a meaningful interpretation of the equations for the steady-state queue length distribution of the GI/GI/c/K queue so that the equations are better understood and become more applicable. As a byproduct, we present an exact expression of the mean queue waiting time for the M/GI/c queue.

• The KIPS Transactions:PartC
• /
• v.9C no.6
• /
• pp.865-874
• /
• 2002

HTTP (HyperText Transfer Protocol) is a transfer protocol used by the World Wide Web distributed hypermedia system to retrieve the objects. Because HTTP is a connection oriented protocol, it uses TCP (Transmission control Protocol) as a transport layer. But it is known that HTTP interacts with TCP badly. it is discussed about factors affecting the performance or HTTP over TCP, the transaction time obtained by the per-transaction TCP connections for HTTP access and the TCP slow-start overheads, and the transaction time for T-TCP (Transaction TCP) which is one or methods improving the performance or HTTP over TCP. Average waiting time and average turnaround time are important parameters to satisfy QoS (Quality of Service) of end users. Formulas for calculating two parameters are derived. Such formulas can be used for the environment in which each TCP or T-TCP transaction time is same or different. Some experiments and computational experiences indicate that the proposed formulas are well acted, can be applied to the environment which the extension of bandwidth is necessary, and time characteristics of T-TCP are superior to that of TCP. Also, the load distribution method of web server based on the combination of bandwidths is discussed to reduce average waiting time and average turnaround time.