Chapter 2 Simulation Examples in a Spreadsheet Figure 2.4 Departure event flow diagram. 3. Develop and interpret flow diagrams analogous to Figures 2.4 and 2.5 for a queueing system with i channels. the queue, server status changes to idle; if there are one or more units waiting, the next unit begins service. In both cases, the number of units in the system decreases by one. The flow diagram for the arrival event is shown in Figure 2.5. The unit finds the server either idle or busy; therefore, either the unit begins service immediately, or it enters the queue. The unit follows the course of action shown in Figure 2.6. If the server is busy, the unit enters the queue. If the server is idle and the queue is empty, the unit begins service. It is not possible for the server to be idle while the queue is nonempty. Figure 2.5 Arrival event flow diagram