Q. Explain Discrete-event simulation?

Discrete-event simulation: Operation of a system is signified as a chronological sequence of events. Every event take place at an instant in time and marks a change of state in the system. For illustration, if an elevator is simulated, an event can be "level 6 button pressed", with the resulting system state of "lift moving" and ultimately (unless one chooses to simulate the failure of the lift) "lift at level 6".

A common exercise in learning how to build discrete-event simulations is to model a queue, like customers arriving at a bank to be served by a teller. In this instance, system entities are CUSTOMER-QUEUE and TELLERS. System events are CUSTOMER-ARRIVAL and CUSTOMER-DEPARTURE. (Event of TELLER-BEGINS-SERVICE can be part of the logic of the arrival and departure events.) The system states, which are changed by these events, are NUMBER-OF-CUSTOMERS-IN-THE-QUEUE (an integer from 0 to n) and TELLER-STATUS (busy or idle). The random variables which need to be characterised to model this system stochastically are CUSTOMER-INTERARRIVAL-TIME as well as TELLER-SERVICE-TIME.