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The North American Numbering Plan (NANP) is a telephone numbering plan that encompasses 25 distinct regions in twenty countries primarily in North America, including the Caribbean and the U.S. territories. Not all North American countries participate in the NANP. Each participating country forms a regulatory authority that has plenary control over local numbering resources.〔(【引用サイトリンク】publisher=Neustar )〕 The NANP was originally devised in the 1940s by AT&T for the Bell System to unify the diverse local numbering plans that had been established in the preceding decades. Since shortly after the breakup of the Bell System, the numbering plan has been administered by the North American Numbering Plan Administration (NANPA), a service that is procured from the private sector by the Federal Communications Commission (FCC) in the United States. The FCC also serves as the U.S. regulator. Canadian numbering decisions are made by the Canadian Numbering Administration Consortium. The NANP divides the territories of its members into numbering plan areas (NPAs) which are encoded numerically with a three-digit telephone number prefix, commonly called the area code.〔(【引用サイトリンク】url=http://www.nanpa.com/area_codes/ )〕 Each telephone is assigned a seven-digit telephone number unique only within its respective plan area consisting of a three-digit central office code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in the public switched telephone network (PSTN). For international call routing, the NANP has been assigned the international calling code 1 by the International Telecommunications Union (ITU). The North American Numbering Plan conforms with ITU Recommendation E.164, which establishes an international numbering framework. ==History== From its beginnings in 1876 and throughout the first part of the 20th century, the Bell System grew from essentially local or regional telephone systems. These systems expanded by growing their subscriber bases, as well as increasing their service areas by implementing additional local exchanges that were interconnected with tie trunks. It was the responsibility of each local administration to design telephone numbering plans that accommodated the local requirements and growth. As a result, the Bell System as a whole developed into an unorganized system of many differing local numbering systems. The diversity impeded the efficient operation and interconnection of exchanges into a nationwide system for long-distance telephone communication. By the 1940s, the Bell System set out to unify the various numbering plans in existence and developed the North American Numbering Plan as a unified, systematic approach to efficient long-distance service that eventually did not require the involvement of switchboard operators. The new numbering plan divided the North American continent into regional service areas, called Numbering Plan Areas (NPA), primarily based on the boundaries of states and provinces. Each NPA was identified by a three-digit code number. The Numbering Plan Areas were created in accordance with principles that were deemed to maximize customer understanding and minimize the dialing effort, while reducing plant cost.〔''Notes on the Network'', AT&T (1980)〕 The plan was designed so that any telephone within the service territory was identified by a unique 10-digit destination routing address. The leading part of this address was the area code (three digits), followed by a seven-digit subscriber number consisting of three digits for the central office exchange and four digits for the station or line number. Typical switching systems of the time were designed to serve up to 10,000 telephones, hence requiring four digits. The central office code was chosen such that it could be represented by the first two letters of the central office name according to a digit-to-letter mapping that was printed on the face of a rotary dial, by grouping a set of letters with the digits ''2'' through ''9''. Such letter translations, designed by W.G. Blauvelt in 1917, had been used in the Bell System in large metropolitan areas since the late 1910s.〔Bell Telephone Laboratories, ''A History of Engineering and Science in the Bell System - The Early Years (1875-1925)'', M.D. Fagan (ed.), 1975, p.126〕 The network reorganization eventually resulted in a 2-letter 5-digit (2L-5N) representation of telephone numbers for every exchange in North America. The new network design, completed in 1947, provided for 152 area codes, each with a capacity to serve 540 central offices.〔 Originally only 86 area codes were assigned. New Jersey received the first area code in the new system, area code 201.〔("Now You Can Call, If Your Calls Don't Work Some Business Lines Aren't Set Up To Call To New Area Codes" ), ''The Virginian-Pilot'', November 1, 1995. Accessed June 8, 2007. "When the first area code, 201, was introduced in New Jersey in 1951, phone-numbering experts thought there would be enough codes with a middle digit of ''0'' or ''1'' to last well into the next century."〕 The second area code, 202 was assigned to the District of Columbia. The allocation of area codes was readjusted as early as 1948 to account for inadequacies in some metropolitan areas. For example, Indiana area code 317 was split to provide a larger number pool in the Indiana suburbs of Chicago (area code 219). Area codes were first used by long-distance operators to establish long-distance calls between toll offices. The first customer-dialed direct call using area codes was made on November 10, 1951, from Englewood, New Jersey, to Alameda, California.〔(1951: First Direct-Dial Transcontinental Telephone Call ), AT&T Corporation. Accessed June 8, 2007. "Nov. 10, 1951: Mayor M. Leslie Downing of Englewood, N.J., picked up a telephone and dialed 10 digits. Eighteen seconds later, he reached Mayor Frank Osborne in Alameda, Calif. The mayors made history as they chatted in the first customer-dialed long-distance call, one that introduced area codes."〕 Direct distance dialing (DDD) was subsequently introduced across the country and by the early 1960s most areas of the Bell System had been converted and it was commonplace in cities and most larger towns. In the following decades, under an independent administration provided by Lockheed Martin IMS and later Neustar, the system grew to include the United States and its territories, Canada, Bermuda, and 17 nations of the Caribbean.〔(NANPA : North American Numbering Plan Administration – About Us )〕 At the request of the British Colonial Office, the numbering plan was first expanded to Bermuda and the British West Indies because of their historic telecommunications administration through Canada as parts of the British Empire, and their continued associations with Canada, especially during the years of the telegraph and the All Red Line system. Not all North American countries participate in NANP, including Mexico, the Central American countries and some Caribbean countries (Cuba, Haiti, and the French Caribbean) that are not part of the system. The only independent Spanish-speaking state in the plan is the Dominican Republic. Mexican participation was planned, but implementation stopped after two area codes were put into use (Mexico City and northwestern Mexico); these were withdrawn from use in 1991. Dutch-speaking Sint Maarten joined the NANP in September 2011.〔 Saint Pierre and Miquelon (+508) and Greenland (+299), both North American possessions of European Union nations, use non-NANP codes which are independent of their respective home countries (+33 France and +45 Denmark). Until 1991, calls to some areas of Mexico from the United States and Canada were made using NANP area codes, but Mexico discontinued participation in the NANP in favor of an international format, using country code +52. Area code 905 (formerly Mexico City) was reassigned to a split of area code 416 (the Greater Toronto Area); area code 706 (formerly northwest Mexico) was reassigned to northern Georgia, surrounding the Atlanta region which retained 404; and area code 903, which also served a small portion of northern Mexico, was reclaimed and later reassigned to northeastern Texas when it split from area code 214. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「North American Numbering Plan」の詳細全文を読む スポンサード リンク
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