Bicycles arrive randomly and their interarrival times are exponentially distributed with mean 5 minutes. Processing sequence is station 1, station 2, station 3 and then station 4. The gear and wheel assembly requires two non-identical processes and hence two different machines. The operations of wheel assembly (station 4) can be performed in any order, but both have to be performed for each arriving bicycle. Bicycle joins the queue of the 4th station operation with the least number of bicycles waiting on one of the two wheel assembling units at that time (since there is no sequencing requirement), and on completion joins the queue of the other wheel assembling unit after which it departs from the system. While joining the other wheel assembling unit, priority is given to that bicycle which has already fitted with one wheel. It is required to complete an order of 5000 bicycles with continuous day-night production. Production will stop once the order is completed as it is a make-to-order production unit.

Draw a schematic diagram of the model, please, with brief explanations.