Chapter18

# Chapter18 - CHAPTER 18 WAITING LINES Teaching Notes Some of...

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CHAPTER 18 WAITING LINES Teaching Notes Some of the math and calculations can be left out in order to focus more clearly on the concepts of waiting lines. For example, all infinite source problems, including single channel (except constant service time) can be handled using the infinite source queuing table. In the past, queuing presented students with a good bit of computational requirements, and because of that, students frequently lost sight of the underlying concepts. With less emphasis on math of calculations, students can handle individual problems more quickly, allowing an instructor to assign a greater number of homework problems, and hopefully enabling students to enrich their experience with queuing vis a vis a variety of (short) problems. If you want to shorten the material somewhat, I would suggest omitting the finite source model and/or the multiple priority model. You can shorten the section even more by not assigning problems which require cost comparisons, although I personally feel that cost comparisons are perhaps the ultimate goal in an operations management course. Answers to Discussion and Review Questions 1. Queuing analysis is appropriate in analyzing capacity when service and/or arrival rates are highly variable. 2. Variations in service and/or arrival rates create instances in which demand temporarily exceeds capacity. 3. Commonly used measures of system performance include the average number waiting and average time they wait, in either the line or the system. In addition, system utilization and total cost are important. 4. The effective system capacity would increase. Consequently, the system could tolerate a higher arrival rate without experiencing a disproportionate increase in waiting time. 5. Supermarkets advertise specials early in the week in an attempt to attract customers on slower days and to spread out arrivals over the week instead of having them bunch up on weekends. They also schedule additional workers during busy hours, and increase flexibility by having stock clerks operate registers and bag orders during busy periods. 6. An infinite source model applies when system entry is unrestricted, or when the potential number of arrivals exceeds the system capacity. A finite source exists when the system caters to a small, limited number of potential customers. 7. The multiple priority approach is appropriate whenever the cost or criticalness of waiting for service differs significantly for different customer (categories). 8. Among the possibilities: meet your neighbors, keep you from wandering around, eliminate line switching, and allow one to analyze the system using the multiple channel model (which assumes a single waiting line). Other than those, the single line serves to reduce the variability of waiting times.

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