In this tutorial, we will go through a performance analysis of QTP Gas Emporium. This is a fictional gas station, illustrated above, that we will use to demonstrate the use of the Queueing ToolPak.
Note: This tutorial illustrates the analysis of a so-called "Markovian queueing system." All functions for analysing such systems have names that begin with "QTPMMS_". A separate tutorial (Tutorial 2) illustrates the analysis of more general types of queueing systems.
To go through the tutorial, you need to have Microsoft Excel open and QTP version 4 installed. You may wish to print this tutorial before you start. The material in this tutorial becomes progressively more conceptually challenging. If you are new to the analysis of waiting lines you may wish to go through the first part of the tutorial and then stop when the going gets rough and return to the tutorial later when you have become more comfortable with the concepts.
The tutorial assumes that you are comfortable with the following Excel operations:
The tutorial was written using Excel 2002.
QTP Gas Emporium has 4 pumps, as shown in the picture above. Arriving cars intending to purchase gas enter the station as long as less than 5 cars are waiting for service (in addition to 4 cars at the pumps). If 5 cars are waiting for service, then arriving cars will balk (not enter the station).
In the terminology of queueing theory, the 4 pumps are the servers, the arriving cars are the customers, and the queue capacity is 5.
To analyze this system using the Queueing ToolPak, one needs to measure the arrival rate and the service rate. Analysis of company records shows that the average number of cars served between 5 and 6 PM on weekdays is 50 (this is the arrival rate). A recent study showed that a car ties up a pump while getting gas for an average of 3 minutes (this is not the service rate -- more on that later).