Analyzing waiting-line problems begins with a description of the situation’s basic elements. Each specific situation will have different characteristics, but four elements are common to all situations:
An input, or customer population, that generates potential customers
A waiting line of customers
The service facility, consisting of a person (or crew), a machine (or group of machines), or both, necessary to perform the service for the customer
A priority rule, which selects the next customer to be served by ...