Draw the stroboscope network.

Vessels arrive with the inter- arrival time being exponentially distributed with the mean value of 20 minutes. When a vessel arrives at the outer port, a tugboat will go to tow it to the terminal. The duration for the vessel to move to the terminal has a triangular distribution T1=[10,20,40]. The vessel will then be moored at the terminal and unload cargos; the unload duration has T2= Triangular [60,90,150]. While the vessel is unloading, the tugboat will return to the outer port. After unloading is finished, the vessel will call a tugboat to tow it back to the outer port and then leave; this task takes T3=Triangular [5,10,30] to complete. Assume the time for the tugboat to move alone is negligible.