The ARPA network wasn’t intended as a real-time system, not in the same sense of the word that true real-timers understand it. (Anything that takes more than 10 to 20 milliseconds, the point at which delays become humanly perceptible, is not considered real-time.) Strictly speaking, the ARPA network was to be a store-and-forward system. But data would zip in and out of the nodes so quickly, and the response time from a human perspective would be so rapid, that it qualified as a real-time problem.
