An automated call distribution system, commonly known as automatic call distributor (ACD), is a telephony device that answers and distributes incoming calls to a specific group of terminals or agents within an organization. ACDs often use a voice menu to direct callers based on the customer's selection, telephone number, selected incoming line to the system or time of day the call was processed. Computer telephony integration (CTI) and computer-supported telecommunications applications (CSTA) are intermediate software that can produce advanced ACD systems. Experts claim that "the invention of ACD technology made the concept of a call centre possible."^[1][2][3]

Private Branch Exchange (PBX) was a telephone exchange device that acted as a mini-switchboard to route phone calls. The closed nature of PBXs limited flexibility, and a system was designed to enable common computing devices to make routing decisions. The automated form of this technology developed into the automated call distribution system, where issued information about incoming calls would direct a response.^[4][5]

Although ACDs appeared in the 1950s, one of the first large and separate ACDs was a modified 5XB switch used by the New York Telephone Company in the early 1970s to distribute calls among hundreds of 4-1-1 information operators. Robert Hirvela developed and received a patent for technology that was used to create the Rockwell Galaxy Automatic Call Distributor, which was used by Continental Airlines for more than 20 years. Since then, ACDs have integrated incoming call management and voice messaging software into its capabilities.^[6][7]

ACDs route incoming calls to the most qualified employee or employees within a company that can address a caller's needs. The technology can also use rule-based instructions such as caller ID, automatic number identification, interactive voice response or dialed number identification services to determine how calls are handled. ACD systems are often found in offices that handle large volumes of incoming phone calls from callers who have no need to talk to a specific person, but require assistance from any of multiple persons (e.g., customer service representatives or emergency services dispatch centers) at the earliest opportunity.

There are several contact routing strategies that can be set up within an algorithm based on a company's needs. Skills-based routing is determined by an operator's knowledge to handle a caller's inquiry. Virtual contact centers can also be used to aggregate the skill sets of agents to help multiple vendors, where all real-time and statistical information can be shared amongst the contact center sites. An additional function for these external routing applications is to enable Computer telephony integration (CTI), which improves efficiency for call center agents by matching incoming phone calls with relevant data via screen pop.^[8][9]

The system has been met with criticism for making small improvements based on customer feedback.^[10] In Florida, ACD technology was installed in several counties for 9-1-1 operators to aid in unanswered phone calls. However, call-takers are not familiar with the geography of the entire county due to the automated system sending calls to the first available responder.^[11]

There are multiple choices for distributing incoming calls from a queue