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"How direct long distance dialing made the U.S. a smaller place, and how instantaneous direct communication between Americans without operator assistance became possible."
Public domain film from the Library of Congress Prelinger Archive, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization (the resulting sound, though not perfect, is far less noisy than the original).
Direct distance dialing (DDD) or direct dial is a telecommunications term for a network-provided service feature in which a call originator may, without operator assistance, call any other user outside the local calling area. DDD requires more digits in the number dialed than are required for calling within the local area or area code. DDD also extends beyond the boundaries of national public telephone network, in which case it is called international direct dialing or international direct distance dialing (IDDD).
DDD is a North American Numbering Plan term considered obsolete since completing a call in any manner other than direct dialing became rare. In the United Kingdom and other parts of the Commonwealth of Nations, the equivalent terms are or were "STD", for subscriber trunk dialing, and "ISD" for international subscriber trunk dialing.
The telephone industry made a United States "first" in the New Jersey communities of Englewood and Teaneck with the introduction of what is known now as direct distance dialing. Starting on November 10, 1951, customers of the ENglewood 3, ENglewood 4 and TEaneck 7 exchanges (who could already dial New York City and area) were able to dial 11 cities across the United States, simply by dialing the three-digit area code and the seven digit number (which at the time consisted of the first two letters of the exchange name and five digits).
The 11 cities and their area codes at that time were:
- Boston, Massachusetts (617)
- Chicago, Illinois (312)
- Cleveland, Ohio (216)
- Detroit, Michigan (313)
- Milwaukee, Wisconsin (414)
- Oakland, California (415)
- Philadelphia, Pennsylvania (215)
- Pittsburgh, Pennsylvania (412)
- Providence, Rhode Island (401)
- Sacramento, California (916)
- San Francisco (318) -- San Francisco required the special area code 318 for temporary routing requirements
Many other cities could not yet be included as they did not yet have the necessary switching equipment to handle incoming calls automatically on their long-distance calling circuits. Other cities still had either a mixture of local number lengths or were all still six-digit numbers; Montreal and Toronto, Canada, for example, had a mix of six- and seven-digit numbers from 1951 to 1957, and did not have DDD until 1958. Whitehorse, Yukon, had seven-digit numbers from 1965, but the necessary switching equipment was not in place locally until 1972.
The Number 4 Crossbar, or 4XB switch, had been introduced in the 1940s to switch four-wire circuits and replace the incoming operator. With semiautomatic operation analogous to the early days of panel switch, the operator in the originating city used a multifrequency keypad to dial an access code to connect to the correct city and to send the seven digit number to incoming equipment at the terminating city. This design was further refined to serve DDD.
The card sorter of the 4A/CTS (Number 4A Crossbar / Card Translator System) allowed six digit translation of the central office code number dialed by the customer. This determined the proper trunk circuits to use, where separate circuit groups were used for different cities in the same area code, as in the case of Oakland and San Francisco. The new device used metal cards similar in principle to computer punched cards, and they were rapidly scanned as they fell past a light beam. On busy days, it sounded like a machine gun firing. CTS machines were called 4A (Advanced) if the translator was included in the original installation, and 4M (Modified) if it was added later. A 1970s version of 4XB, the 4A/ETS, used a computer to translate. For international dialing, TSPS provided the extra computer power.
The reach of DDD was limited due to the inefficiency and expense of switching equipment, and the limited ability to process records of completed calls...