Customers arriving from different flows are treated equally by placing into the queues, respecting strictly, their arriving order. Already in the queue are served in the same order they entered, this means, first customer that comes in the queue is the first one that goes out.
All customers arriving in the queuing system will be served approximately equally distributed service time and being served in an order of first come first serve, whereas customer choose a queue randomly, or choose or switch to shortest length queue. There is no limit defined for number of customers in a queue or in a system.