For example, the Internet may be constructed as a Communications System. The functional components would be the items of Input, Disturbance, Output, Comparator, Feedback, and Damping.
Incomplete packets exceed acceptable limits.
No DNS entry. Comparators, which indicate whether the message that got through is the same message that was sent, could include physical contact between participants. Feedback could include determining whether the message that came through made sufficient sense, or whether it needed to be communicated again. These pieces are important, they support the Functions of the System being accomplished, but they themselves do not constitute the system's functions. The overriding goal of the auto cruise-control is to maintain its performance at its ideal condition.