The intention of this article is to give a brief overview of the modern day directory assistance system.

The modern day directory assistance system has come a long way from the early days of 411 when operators used to look up numbers on index cards. The directory assistance system was set up for the purpose of helping telephone subscribers look up the phone numbers of other subscribers. The service is provided by an operator who is connected to the subscriber through an electronic switching system. The early systems were very crude and required operators to go through books and file cards to find telephone numbers. Eventually, the amount of traffic for directory assistance increased and a more efficient and quicker system was needed.

The modern system in use in most places today dates back to United States patent 4,677,609 which was granted on June 30, 1987. This is basically a communication assistance system designed for utilizing computer aided directory number services.

Trying to keep the explanation of how the system works as simple as possible, the system itself was manufactured by It provides the directory assistance operator with a terminal for communicating with the main directory assistance computer. What happens is that a subscriber's call requesting directory assistance is routed by a special trunk that's connected to a switching network, which establishes a voice connection with the operator and is then connected to an audio response unit. For each incoming call the operator makes a verbal request of the subscriber for the name and address of the party they are trying to reach. After the operator gets this information he or she relays this information to the main directory assistance computer via the terminal. Then, the audio response unit gets the data from the network controller. When the computer locates the number it sends a message to the audio response unit which then generates an audible directory announcement which represents the number that the subscriber asked for. This way the operator doesn't have to repeat the number and worry about being understood by the subscriber.

This system is not cheap. It requires the use of special purpose trunks to connect the customer to the switching network and then to the audio response unit. Also, the audio response unit needs a large number of output ports that are permanently connected to each special purpose trunk circuit. A system like this needs two different control units, one for the switching network and one to the audio response unit. This further adds to the cost as these units are very complex. Plus the system as it is currently set up can only handle one call at a time. This causes delays, especially for lengthy communications.

The good news is that new designs are being looked into everyday in order to make the process quicker and cheaper, including looking into more modular designs as well as cordless operation and digital systems.

While we still have a long way to go to get the directory assistance system that is most efficient, we have certainly come a long way from books and file cards.