Direct distance dialing

From Free net encyclopedia

Direct Distance Dialing (DDD) 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. DDD also extends beyond the boundaries of national public telephone networks.

Direct distance dialing (DDD) is a North American Numbering Plan term, and considered obsolete as calls are now rarely completed in any other manner. In the United Kingdom and other parts of the Commonwealth of Nations, the equivalent term is or was "STD", for subscriber trunk dialling.

Source: partly from Federal Standard 1037C and from MIL-STD-188

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History

The telephone industry made a United States "first" in the New Jersey communties of Englewood and Teaneck with the introduction of what is known now as Direct distance dialing (DDD). 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 (or the three-digit area code and the local number of two letters and five digits).

The 11 cities and their area codes at that time were:

Many other cities could not yet be included as they did not yet have the necessary switching equipment to automatically handle incoming calls on their long distance 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.

At the time, New York City's five boroughs were dialed from Englewood and Teaneck with the digits '1-1' followed by the two letters of the Exchange Name and then the remaining five digits. While New York City was assigned Area Code 212 at the very beginning of the Area Code format in October 1947, it wouldn't be until later in the 1950s when Englewood customers would dial their calls to New York City using the digits 2-1-2. The use of the '11+' code from Englewood (and other parts of northeastern New Jersey) to call New York City had been in place for a while, even prior to 1951. New York City's five boroughs also had been dialing northeastern New Jersey as 11+ the two letters and five digits of the New Jersey number as well for a while prior to 1951 and until the later 1950s. The use of the 201 area code to call New Jersey from New York City didn't begin until the later 1950s. Englewood and Teaneck customers in 1951 didn't even know that their own area code was 201! Other cities in northeastern New Jersey, both local and toll, were dialable in 1951 (and for a few years prior) from Englewood by simply dialing the two letters of the Exchange Name and remaining five digits. In addition to New York City, the Nassau County part of Long Island was dialable from Englewood and Teaneck using area code 516; also Westchester County, Rockland County, and portions of Orange and Putnam Counties were also dialable from Englewood and Teaneck in 1951 using area code 914.

The card sorter allowed the central office code number dialed by the customer to be scanned to determine the proper trunk circuits to use for a city 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 punch cards, and they were rapidly scanned as they fell past a light beam. On busy days, it sounded like a machine gun firing!

The reach of direct distance dialing was limited due to the inefficiency and expense of switching equipment, and the limited ability to process records of completed calls.

As this and other improved technologies became available, as well as computers to process the long distance records into customer bills, the reach of DDD was slow in the 1950s, but quickened in the early 1960s. Electronic switching systems with stored-program capability allowed electronic processing of the dialed digits, referring to electronic memories to determine call routing, and this has reached the state-of-the-art with digital exchanges which are basically specialized computers that route voice traffic from one "peripheral" to another as digital data. Call routing can now be done based on the area code, central office code and even the first two digits of the line number, although routing based on digits past the central office code is usually limited to cases of competitive local carriers and number portability.

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