As one of the basic tenets of customer care, call routing has been around for about as long as the call center, and the contact center, have been around. Basic call routing, where the incoming call gets routed to the first available agent, came into existence along with the first automatic call distributor (ACD) in 1973. This revolutionary method of getting customer calls to customer service representatives meant that customers didn't receive a busy signal when there were no agents available when they called. Rather, they waited in a call queue until an agent became available and the call was connected. This method of connecting callers with agents didn't change in its essence until the advent of skills-based routing.