Direct distance dialing (DDD) is a

telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

service in North America by which a caller may call any other

subscriber The subscription business model is a business model in which a customer must pay a recurring price at regular intervals for access to a product or service. The model was pioneered by publishers of books and periodicals in the 17th century. It i ...

outside the local calling area without

operator assistance Operator assistance refers to service provided by a telephone operator to the calling party of a telephone call. This can include telephone calls made from pay phones, calls placed ''station-to-station'', ''person-to-person'', or ''collect'', ...

, DDD was introduced in the United States in 1951, on a trial basis, with service from Englewood, New Jersey. Direct long-distance dialing by subscribers requires extra digits, called an

area code A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, rea ...

, to be dialed as prefixes to the directory telephone number of the destination. International Direct Distance Dialing (IDDD) extends the system beyond the geographic boundaries of the

North American Numbering Plan The North American Numbering Plan (NANP) is an integrated telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1, World Numbering Zone ...

(NANP).

History

The first direct-dialed long-distance telephone calls were possible in the

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

communities of Englewood and

Teaneck Teaneck () is a township in Bergen County, in the U.S. state of New Jersey. It is a bedroom community in the New York metropolitan area. The town is know for their pancake throwing contest held every September. As of the 2020 United States cen ...

. Customers of the ENglewood 3, ENglewood 4 and TEaneck 7 exchanges, who could already dial telephone numbers in the New York City area, could place calls to eleven major cities across the United States by dialing the three-digit

and the seven-digit directory number. Local telephone numbers still consisted of the first two letters of the

central office name A telephone exchange name or central office name was a distinguishing and memorable name assigned to a telephone exchange, central office. It identified the switching system to which a telephone was connected, and facilitated the connection of te ...

and five digits. On November 10, 1951, Englewood mayor M. Leslie Denning made the first customer-dialed

long-distance call In telecommunications, a long-distance call (U.S.) or trunk call (also known as a toll call in the UK ) is a telephone call made to a location outside a defined local calling area. Long-distance calls are typically charged a higher billing rate ...

, to Mayor Frank Osborne of

Alameda, California Alameda ( ; ; Spanish for "Avenue (landscape), tree-lined path") is a city in Alameda County, California, United States, located in the East Bay (San Francisco Bay Area), East Bay region of the Bay Area. The city is built on an informal archipe ...

. The destinations, and their area codes, equipped with a long-distance toll-switch at that time were: *

617 __NOTOC__ Year 617 ( DCXVII) was a common year starting on Saturday of the Julian calendar. The denomination 617 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Euro ...

Boston Boston is the capital and most populous city in the Commonwealth (U.S. state), Commonwealth of Massachusetts in the United States. The city serves as the cultural and Financial centre, financial center of New England, a region of the Northeas ...

, Massachusetts *

312 __NOTOC__ Year 312 (Roman numerals, CCCXII) was a leap year starting on Tuesday of the Julian calendar. In the Roman Empire, it was known as the Year of the Consulship of Constantinus and Licinianus (or, less frequently, year 1065 ''Ab urbe co ...

Chicago Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...

, Illinois *

216 __NOTOC__ Year 216 ( CCXVI) was a leap year starting on Monday of the Julian calendar. At the time, it was known as the Year of the Consulship of Sabinus and Anullinus (or, less frequently, year 969 ''Ab urbe condita''). The denomination 216 f ...

Cleveland Cleveland is a city in the U.S. state of Ohio and the county seat of Cuyahoga County. Located along the southern shore of Lake Erie, it is situated across the Canada–U.S. maritime border and approximately west of the Ohio-Pennsylvania st ...

, Ohio *

313 __NOTOC__ Year 313 ( CCCXIII) was a common year starting on Thursday of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantinus and Licinianus (or, less frequently, year 1066 ''Ab urbe condita''). The denom ...

Detroit Detroit ( , ) is the List of municipalities in Michigan, most populous city in the U.S. state of Michigan. It is situated on the bank of the Detroit River across from Windsor, Ontario. It had a population of 639,111 at the 2020 United State ...

, Michigan *

414 __NOTOC__ Year 414 ( CDXIV) was a common year starting on Thursday of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantius and Constans (or, less frequently, year 1167 ''Ab urbe condita''). The denominati ...

Milwaukee Milwaukee is the List of cities in Wisconsin, most populous city in the U.S. state of Wisconsin. Located on the western shore of Lake Michigan, it is the List of United States cities by population, 31st-most populous city in the United States ...

, Wisconsin *

415 __NOTOC__ Year 415 ( CDXV) was a common year starting on Friday of the Julian calendar. At the time, it was known as the Year of the Consulship of Honorius and Theodosius (or, less frequently, year 1168 ''Ab urbe condita''). The denomination ...

Oakland Oakland is a city in the East Bay region of the San Francisco Bay Area in the U.S. state of California. It is the county seat and most populous city in Alameda County, with a population of 440,646 in 2020. A major West Coast port, Oakland is ...

, California *

215 Year 215 ( CCXV) was a common year starting on Sunday of the Julian calendar. At the time, it was known as the Year of the Consulship of Laetus and Sulla (or, less frequently, year 968 ''Ab urbe condita''). The denomination 215 for this year ha ...

Philadelphia Philadelphia ( ), colloquially referred to as Philly, is the List of municipalities in Pennsylvania, most populous city in the U.S. state of Pennsylvania and the List of United States cities by population, sixth-most populous city in the Unit ...

, Pennsylvania *

412 __NOTOC__ Year 412 ( CDXII) was a leap year starting on Monday of the Julian calendar. At the time, it was known in Europe as the Year of the Consulship of Honorius and Theodosius (or, less frequently, year 1165 ''Ab urbe condita''). The denom ...

Pittsburgh Pittsburgh ( ) is a city in Allegheny County, Pennsylvania, United States, and its county seat. It is the List of municipalities in Pennsylvania#Municipalities, second-most populous city in Pennsylvania (after Philadelphia) and the List of Un ...

, Pennsylvania *

401 __NOTOC__ Year 401 ( CDI) was a common year starting on Tuesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Vincentius and Fravitus (or, less frequently, year 1154 ''Ab urbe condita''). The denomination ...

Providence, Rhode Island Providence () is the List of capitals in the United States, capital and List of municipalities in Rhode Island, most populous city of the U.S. state of Rhode Island. The county seat of Providence County, Rhode Island, Providence County, it is o ...

916 __NOTOC__ Year 916 ( CMXVI) was a leap year starting on Monday of the Julian calendar. Events By place Europe * Sicilian Berbers in Agrigento revolt and depose the independent Emir Ahmed ibn Khorob. They offer Sicily to the Fatimid C ...

Sacramento Sacramento ( or ; ; ) is the capital city of the U.S. state of California and the seat of Sacramento County. Located at the confluence of the Sacramento and American Rivers in Northern California's Sacramento Valley, Sacramento's 2020 p ...

, California *

318 Year 318 ( CCCXVIII) was a common year starting on Wednesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Licinianus and Crispus (or, less frequently, year 1071 ''Ab urbe condita''). The denomination 318 fo ...

San Francisco San Francisco, officially the City and County of San Francisco, is a commercial, Financial District, San Francisco, financial, and Culture of San Francisco, cultural center of Northern California. With a population of 827,526 residents as of ...

, California Other areas could not yet be included in DDD as they did not have the necessary toll switching equipment, or because they still did not use a seven-digit local numbering plan.

Montreal Montreal is the List of towns in Quebec, largest city in the Provinces and territories of Canada, province of Quebec, the List of the largest municipalities in Canada by population, second-largest in Canada, and the List of North American cit ...

Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...

, and

Toronto Toronto ( , locally pronounced or ) is the List of the largest municipalities in Canada by population, most populous city in Canada. It is the capital city of the Provinces and territories of Canada, Canadian province of Ontario. With a p ...

Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...

, in Canada, for example, had a mix of six- and seven-digit telephone numbers from 1951 to 1957, and did not have DDD until 1958.

Whitehorse Whitehorse () is the capital of Yukon, and the largest city in Northern Canada. It was incorporated in 1950 and is located at kilometre 1426 (Historic Mile 918) on the Alaska Highway in southern Yukon. Whitehorse's downtown and Riverdale areas ...

Yukon Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...

, had seven-digit numbers starting in 1965, but the necessary switching equipment was not in place until 1972. San Francisco required the special area code 318 due to temporary routing requirements. San Francisco and Oakland each had their own separate toll-switches, so calls had to be routed accordingly depending on the final destination. As the telephone equipment used at the time could only handle three-digit translation, the temporary use of area code 318 was required to distinguish between the two areas. Area code 318 was temporarily used to specify San Francisco and areas north of the

Golden Gate The Golden Gate is a strait on the west coast of North America that connects San Francisco Bay to the Pacific Ocean. It is defined by the headlands of the San Francisco Peninsula and the Marin Peninsula, and, since 1937, has been spanned by ...

, while calls with destinations in

and the

East Bay The East Bay is the eastern region of the San Francisco Bay Area and includes cities along the eastern shores of San Francisco Bay and San Pablo Bay. The region has grown to include inland communities in Alameda and Contra Costa counties. Wi ...

continued to use area code 415. When the electromechanical card-translator box became available in the 1952–53 period, six-digit translation became possible and the use of area code 318 was no longer required. Area code 318 was reclaimed for future use (now used as an area code for northern

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

), and the entire

San Francisco Bay Area The San Francisco Bay Area, commonly known as the Bay Area, is a List of regions of California, region of California surrounding and including San Francisco Bay, and anchored by the cities of Oakland, San Francisco, and San Jose, California, S ...

returned to using area code 415.

Hardware

The No. 4 Crossbar switching system had been introduced in the early 1940s to switch

four-wire circuit In telecommunications, 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. The four-wire circuit gets its ...

s and replace the incoming operator. With semiautomatic operation analogous to the early days of the

panel switch The Panel Machine Switching System is a type of automatic telephone exchange for urban service that was used in the Bell System in the United States for seven decades. The first semi-mechanical types of this design were installed in 1915 in Newark, ...

, the operator in the originating city used a

multifrequency In telephony, multi-frequency signaling (MF) is a type of signaling that was introduced by the Bell System after World War II. It uses a combination of audible tones for address (telephone number) transport and supervision signaling on trunk line ...

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 A punched card (also punch card or punched-card) is a stiff paper-based medium used to store digital information via the presence or absence of holes in predefined positions. Developed over the 18th to 20th centuries, punched cards were wide ...

, and they were rapidly scanned as they fell past a light beam. 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,

Traffic Service Position System The Traffic Service Position System (TSPS) was developed by Bell Labs in Columbus, Ohio to replace traditional cord switchboards. The first TSPS was deployed in Morristown, New Jersey in 1969 and used the Stored Program Control-1A CPU, "Piggybac ...

(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. An early obstacle was that the majority of switching systems did not provide

Automatic Number Identification Automatic number identification (ANI) is a feature of a telecommunications network for automatically determining the origination telephone number on toll calls for billing purposes. Automatic number identification was originally created by the Am ...

(ANI).

Common control In telecommunications, common control is a principle of switching telephone calls in an automatic telephone exchange that employs shared control equipment which is attached to the circuit of a call only for the duration of establishing or otherwis ...

switches, such as the

1XB switch The Number One Crossbar Switching System (1XB), was the primary technology for urban telephone exchanges served by the Bell System in the mid-20th century. Its switch fabric used the electromechanical crossbar switch to implement the topology of the ...

, were fairly quickly retrofitted to provide ANI, and most

5XB switch The Number Five Crossbar Switching System (5XB switch) is a telephone switch for telephone exchanges designed by Bell Labs and manufactured by Western Electric starting in 1947. It was used in the Bell System principally as a Class 5 telephone swit ...

es were initially installed with ANI services.

Panel switch The Panel Machine Switching System is a type of automatic telephone exchange for urban service that was used in the Bell System in the United States for seven decades. The first semi-mechanical types of this design were installed in 1915 in Newark, ...

were eventually retrofitted, as were some step-by-step systems that were not scheduled for immediate replacement. Even if a switch had ANI, it could not identify callers on party lines. This was only partly overcome by tip-party identification for two-party lines. 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 (AMA) provides detailed accounting for telephone calls. When direct distance dialing (DDD) was introduced in the US, message registers no longer sufficed for dialed telephone calls. The need to record the time and pho ...

(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 In telecommunications, an electronic switching system (ESS) is a telephone switch that uses solid-state electronics, such as digital electronics and computerized common control, to interconnect telephone circuits for the purpose of establishing te ...

s 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 A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...

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 A competitive local exchange carrier (CLEC) is a North American telecommunications provider classification that emerged based on the competition model of the Telecommunications Act of 1996 in the United States. The act required the previously esta ...

number pooling Telephone number pooling, thousands-block number pooling, or just number pooling, is a method of allocating telephony numbering space of the North American Numbering Plan in the United States. The method allocates telephone numbers in blocks of 1,0 ...

and

number portability Telephone number portability can refer to: *Mobile number portability - telephone number portability for mobile phone users. *Local number portability - telephone number portability for landline users. *Toll-free number portability Toll-free numbe ...

IDDD

In the 1960s, with the domestic conversion still underway, plans were laid to extend Direct Distance Dialing beyond North America (including a number of the

Caribbean Islands Most of the Caribbean countries are islands in the Caribbean Sea, with only a few in inland lakes. The largest islands include Cuba, Hispaniola, Jamaica and Puerto Rico. Some of the smaller islands are referred to as a ''rock'' or ''reef.'' ''I ...

). Some subscribers could already directly dial transatlantic telephone calls to certain destinations as early as in 1957 over the recently completed Atlantic cable to England. A new systematic extension of Direct Distance Dialing was developed and was introduced as International Direct Distance Dialing (IDDD) in March 1970.AT&T, ''Notes on Distance Dialing'' (1975) With so much new equipment already working that could not handle more than the requisite ten-digit telephone numbers of DDD, the new system was based on designs by which most toll offices did not have to store and forward the whole international telephone 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 3 (three) is a number, numeral and digit. It is the natural number following 2 and preceding 4, and is the smallest odd prime number and the only prime preceding a square number. It has religious and cultural significance in many societies ...

. The new LT1

on the tenth floor of 435 West 50th Street received new originating registers and outgoing senders able to handle fifteen-digit telephone numbers, with appropriate modifications to completing markers and other equipment. Other 5XB switches 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 In telephony, multi-frequency signaling (MF) is a type of signaling that was introduced by the Bell System after World War II. It uses a combination of audible tones for address ( telephone number) transport and supervision signaling on trunk ...

pulsing. The outgoing sender sent its Class 4 toll center an

off-hook In telephony, on-hook and off-hook are two states of a communication circuit. On subscriber telephones the states are produced by placing the handset onto or off the hookswitch. Placing the circuit into the off-hook state is also called ''seizing ...

signal as usual, received a wink as usual as a "proceed to send" signal, and outpulsed only a special three-digit (later six-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, 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 the

(TSPS). 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.

Equivalent service in the United Kingdom

In the United Kingdom and other parts of the

Commonwealth of Nations The Commonwealth of Nations, often referred to as the British Commonwealth or simply the Commonwealth, is an International organization, international association of member states of the Commonwealth of Nations, 56 member states, the vast majo ...

, an equivalent service to direct distance dialing is

subscriber trunk dialing Subscriber trunk dialling (STD), also known as subscriber toll dialing, is a telephone numbering plan feature and telecommunications technology in the United Kingdom and various Commonwealth countries for the dialling of trunk calls by telephon ...

(STD), and ISD for international subscriber trunk dialing. Queen

Elizabeth II Elizabeth II (Elizabeth Alexandra Mary; 21 April 19268 September 2022) was Queen of the United Kingdom and other Commonwealth realms from 6 February 1952 until Death and state funeral of Elizabeth II, her death in 2022. ...

inaugurated STD on 5 December 1958, when she dialed a call from Bristol to Edinburgh and spoke to the

Lord Provost A lord provost () is the convenor of the local authority, the civic head and the lord-lieutenant of one of the principal cities of Scotland. The office is similar to that of a lord mayor. Only the cities of Aberdeen, Dundee, Edinburgh, Stirlin ...

References

* *

External links