Preemptive (Set-ups):
Change of server: This could be considered a set-up because it is planed during the schedule of the day. They ocurre every certain period of time, always starting at the same hour of the day and ending after the service time period of a worker finishes.
Non Preemptive:
System crash: No body can prevent a system crash. They an ocurre randomly during the service time depending on different factors as the computers condition, power failures or lack of maintenance.
Costumer interruptions: There are certain situations in which a costumer comes back to the office and wants to speak to the server with whom he had talked before. What happens is that the server that costumer is looking for has to leave his cubicle and attend the situation interrupting the current service. This interruptions can ocurre randomly.
