• Event scheduling simulation is modelling over time of a system whose state changes at discrete points in time.

• A discrete event simulation proceeds by producing a sequence of system snapshots that represent the evolution of the system through time. A given snapshot at a given time includes system state at time t and future event list (FEL).

• The FEL contains all previously scheduled future events and their associated event times. Events in FEL are arranged according to chronological order- that is, the event times must satisfy t<=$t_1$<=$t_2$<=$t_3$<=…$t_n$.

• Time t is the value of CLOCK, the current value of simulated time. The event associated with time $t_1$ is called imminent event i.e $t_1$ is the next event that will occur.

• After the system snapshot at simulation time CLOCK=t has been updated , the CLOCK is advanced to simulation time CLOCK=$t_1$. The sequence of actions that a simulator must perform to advance the clock and build a new system snapshot is called the event-scheduling/ time –advance algorithm, whose steps are listed in figure below.

Event Scheduling/ time advance algorithm

Step 1. Remove the event notice for the imminent event (event 3, time$t_1$) from FEL.

Step 2. Advance CLOCK to imminent event time (i.e. advance CLOCK from t to$t_1$)

Step 3. Execute imminent event: update system state, change entity attributes, and set membership as needed.

Step 4. Generate future events (if necessary) and place their event notice on FEL, ranked by event time. (Example: Event 4 to occur at time $t^{+}$, where $t_2$<$t^{+} $<$t_3$ )

Step 5. Update cumulative statistics and counters.