The model consists of three reactive classes: TicketService, Agent, and Customer. Customer sends the ticket issue message to Agent and Agent forwards the issue to TicketService. TicketService rebec replies to Agent by sending a ticket issued message and Agent responds to Customer by sending the issued ticket identifier. As shown in line 12 of the model, issuing the ticket takes three time units (based on the configuration parameters, the issueDelay initial value equals to three). In addition, line 24 shows that Agent waits for five time units for TicketService to take the requested message and starts serving it.