For a queueing system, design deals with the permanent, optimal setting of system parameters (such as service rate and/or number of servers), while control deals with adjusting system parameters as the system evolves to ensure certain performance levels are met. A typical example of a control rule is that a server is to be added when the queue size is greater than a certain number (say N₁) and when the queue size drops down to N₂ < N₁, the server goes to other duties. Dynamic programming;  Markov decision processes;  Queueing theory.