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The solution for expanding the numbering pool within an NPA was to remove the restriction posed by not using 0 and 1 in the middle position of central office codes. This made central office codes interchangeable. An interchangeable NPA code and an interchangeable central office code is a code that permits any of the ten numerals in the middle ...
Central office code protection was once common in communities on provincial or state boundary lines. It has been declining in use as inefficient allocation of numbering resources to the growing number of competitive local exchange carriers has caused depletion of available number prefixes, often requiring ten-digit local calls and overlay plans ...
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 1,000 consecutive numbers of a given central office code to telephony service providers.
In telecommunications, an area code overlay complex is a telephone numbering plan that assigns multiple area codes to the same geographic numbering plan area (NPA). Area code overlays are implemented in territories of the North American Numbering Plan (NANP) to mitigate exhaustion of central office codes in growth areas. The method has been in ...
For example, 234 235-5678 is a valid telephone number; with area code 234, central office prefix (exchange) 235, and line number 5678. The number 234 911-5678 is invalid, because the central office code must not be in the form N11. 314 159-2653 is invalid, because the office code must not begin with 1.
This required 82 area codes to switch to mandatory ten-digit dialing by October 24, 2021, because they had already used 988 as a central office code. [3] Similar transitions are scheduled in most parts of the remaining single-code areas in Canada by May 31, 2023, due in part to the rollout of 9-8-8 service in that country. [4]
California (Stockton, Modesto, Merced, Tracy, San Andreas, and a part of central California extending into central Yosemite National Park) 1958: split of 916; 1998: split to create 559; 2022: overlaid by 350; 210: Texas (San Antonio metropolitan area) November 1, 1992: split of 512; 1997: split three ways to create 830 and 956; 2017: overlaid ...
This increased the numbering pool for central office codes to 640, and resulted in the partitioning of the prefix space (000—999) according to the table at the right. [ 5 ] All-number calling was first field-tested in Wichita Falls, Texas starting on January 19, 1958, with the installation of a new dial exchange. [ 3 ]