Direct distance dialing
Encyclopedia
Direct distance dialing or direct dial is a telecommunications term for a network
Telecommunications network
A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...

-provided service feature in which a call originator may, without operator
Telephone operator
A telephone operator is either* a person who provides assistance to a telephone caller, usually in the placing of operator assisted telephone calls such as calls from a pay phone, collect calls , calls which are billed to a credit card, station-to-station and person-to-person calls, and certain...

 assistance, call any other user
User (telecommunications)
In telecommunications, a user is a person, organization, or other entity that employs the services provided by a telecommunication system, or by an information processing system, for transfer of information....

 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
North American Numbering Plan
The North American Numbering Plan is an integrated telephone numbering plan administered by Neustar which encompasses 24 countries and territories, including the United States and its territories, Canada, Bermuda, and 16 nations of the Caribbean...

 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
Commonwealth of Nations
The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-four independent member states...

, the equivalent terms are or were "STD", for subscriber trunk dialing, and "ISD" for international subscriber trunk dialing.

History

The telephone industry made a United States "first" in the New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...

 communities of Englewood
Englewood, New Jersey
Englewood is a city located in Bergen County, New Jersey. As of the 2010 United States Census, the city had a total population of 27,147.Englewood was incorporated as a city by an Act of the New Jersey Legislature on March 17, 1899, from portions of Ridgefield Township and the remaining portions of...

 and Teaneck
Teaneck, New Jersey
Teaneck is a township in Bergen County, New Jersey, and a suburb in the New York metropolitan area. As of the 2010 United States Census, the township population was 39,776, making it the second-most populous among the 70 municipalities in Bergen County....

 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
Telephone exchange names
During the early years of telephone service, communities that required more than 10,000 telephone numbers, whether dial service was available or not, utilized exchange names to distinguish identical numerics for different customers....

 and five digits).

The 11 cities and their area codes at that time were:
  • Boston, Massachusetts (617)
  • Chicago
    Chicago
    Chicago is the largest city in the US state of Illinois. With nearly 2.7 million residents, it is the most populous city in the Midwestern United States and the third most populous in the US, after New York City and Los Angeles...

    , Illinois (312)
  • Cleveland, Ohio (216)
  • Detroit, Michigan (313)
  • Milwaukee, Wisconsin (414)
  • Oakland, California
    Oakland, California
    Oakland is a major West Coast port city on San Francisco Bay in the U.S. state of California. It is the eighth-largest city in the state with a 2010 population of 390,724...

     (415)
  • Philadelphia, Pennsylvania (215)
  • Pittsburgh, Pennsylvania (412)
  • Providence, Rhode Island
    Providence, Rhode Island
    Providence is the capital and most populous city of Rhode Island and was one of the first cities established in the United States. Located in Providence County, it is the third largest city in the New England region...

     (401)
  • Sacramento
    Sacramento, California
    Sacramento is the capital city of the U.S. state of California and the county seat of Sacramento County. It is located at the confluence of the Sacramento River and the American River in the northern portion of California's expansive Central Valley. With a population of 466,488 at the 2010 census,...

    , California (916)
  • San Francisco (318) – San Francisco required the special area code 318
    Area code 318
    Area code 318 is a telephone area code that covers the central and northern parts of Louisiana. The area code was split off in 1957 from the original area code 504, which had previously covered the entire state....

     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
Montreal
Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...

 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
Whitehorse, Yukon
Whitehorse is Yukon's capital and largest city . It was incorporated in 1950 and is located at kilometre 1476 on the Alaska Highway in southern Yukon. Whitehorse's downtown and Riverdale areas occupy both shores of the Yukon River, which originates in British Columbia and meets the Bering Sea in...

, had seven-digit numbers from 1965, but the necessary switching equipment was not in place locally until 1972.

Hardware

The Number 4 Crossbar, or 4XB switch, had been introduced in the 1940s to switch four-wire circuit
Four-wire circuit
In telecommunication, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path...

s and replace the incoming operator. With semiautomatic operation analogous to the early days of panel switch
Panel switch
The panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s...

, 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. One obstacle was that the majority of switching gear did not provide Automatic Number Identification
Automatic number identification
Automatic number identification is a feature of telephony intelligent network services that permits subscribers to display or capture the billing telephone number of a calling party. In the United States it is part of Inward Wide Area Telephone Service . ANI service was created by AT&T for...

 (ANI). Common control
Common control
In telecommunication, a common control is an automatic telephone exchange arrangement in which the control equipment necessary for the establishment of connections is shared by being associated with a given call only during the period required to accomplish the control function for the given call...

 switches such as 1XB switch were fairly quickly retrofitted to provide ANI, and most 5XB switches were initially installed with ANI services. Panel switch
Panel switch
The panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s...

 were eventually retrofitted, as were some step-by-step
Strowger switch
The Strowger switch, also known as Step-by-Step or SXS, is an early electromechanical telephone switching system invented by Almon Brown Strowger...

 that were not scheduled for immediate replacement. Even if a switch had ANI, it could not identify callers on party lines
Party line (telephony)
In twentieth-century telephone systems, a party line is an arrangement in which two or more customers are connected directly to the same local loop. Prior to World War II in the United States, party lines were the primary way residential subscribers acquired local telephone service...

. This was only partly overcome by Tip Party Identification. As the cost of subscriber line carrier declined, party lines were gradually phased out.

As this and other improved technologies became available, as well as Automatic Message Accounting
Automatic Message Accounting
Automatic message accounting provides detail billing for telephone calls. When direct distance dialing was introduced in the US, message registers no longer sufficed for dialed telephone calls...

 (AMA) 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 system
Electronic switching system
In telecommunications, an electronic switching system is:* A telephone exchange based on the principles of time-division multiplexing of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and interconnects them by assigning the digitized...

s 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 telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

s 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 exchange carrier
Competitive local exchange carrier
A competitive local exchange carrier , in the United States, is a telecommunications provider company competing with other, already established carriers ....

s and number portability.

IDDD

In the 1960s, with the domestic conversion still underway, plans were laid to extend Direct Dialing beyond North America and its nearby islands. With so much new equipment already working that could only handle ten digit phone numbers, a system was devised by which most toll offices did not have to store and forward the whole international phone number. Gateway offices were set up in New York, London and Paris, connected to the ordinary automatic toll network. The New York gateway was at 32 Avenue of the Americas
32 Avenue of the Americas
32 Avenue of the Americas also known as the AT&T Long Distance Building, is a 27-story landmarked Art Deco skyscraper located in the Tribeca neighborhood of New York City. The building reaches a height of 549 feet up to its twin spires, and was completed in 1932...

. The new LT1 5XB switch on the tenth floor of 435 West 50th Street received new 15 digit Originating Registers, Outgoing Senders, and appropriate modifications to Completing Markers and other equipment. Other 5XB in the next few years were installed with IDDD as original equipment, and in the 1970s ESS offices also provided the service.

The key to the new system was two-stage multi-frequency
Multi-frequency
In telephony, multi-frequency signaling is an outdated, in-band signaling technique. Numbers were represented in a two-out-of-five code for transmission from a multi-frequency sender, to be received by a multi-frequency receiver in a distant telephone exchange...

 pulsing. The outgoing sender sent its Class 4 toll center an off-hook
Off-hook
In telephony, the term off-hook has the following meanings:# The condition that exists when a telephone or other user instrument is in use, i.e., during dialing or communicating. Note: off-hook originally referred to the condition that prevailed when telephones had a separate earpiece , which hung...

 signal as usual, received a wink as usual as a "proceed to send" signal, and outpulsed only a special 3-digit (later 6-digit) access code. The toll center picked a trunk through the long distance network to the gateway office, which sent a second wink to the originating office, which then sent the whole dialed number. Thus the toll switching system needed no modification except at the gateway. The international trunks used Signaling System No. 5
Signaling System No. 5
CCITT5 was a multi-frequency telephone signalling system in use from the 1970s for International Direct Distance Dialing . It was sometimes nicknamed "Atlantic Code" because the first IDD connections between Europe and North America used it....

, a "North Atlantic" version of the North American multi-frequency signaling system, with minor modifications including slightly higher digit rate. European MF systems of the time used compelled signaling, which would slow down too much on a long transoceanic connection.

In the 1970s, toll centers were modified by adding TSPS
Traffic Service Position System
Traffic Service Position System was developed by Bell Labs in Columbus, Ohio to replace traditional cord switchboards. The first TSPS was deployed in 1969 and used the Stored Program Control-1A CPU, "Piggyback" twistor memory and IGFET Insulated Gate Field Effect Transistor solid state memory...

. With these new computers in place, digit storage in the toll system was no longer a problem. End offices were less extensively modified, and sent all their digits in a single stream. TSPS handled the gateway codes and other complexities of toll connections to the gateway office.

External links

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