Overlay complex

Source: Wikipedia, the free encyclopedia.
(Redirected from
Area code overlay
)

In

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 use since 1992, and has been the exclusive method of area code relief since 2007.

History

From the inception of the North American Numbering Plan in 1947 until 1992, the only method of introducing new area codes was the

central office codes of the other areas, because those were delegated to a new area code in the process.[1]
The existing central office codes in the separated areas are maintained in the new numbering plan area, so that the only change for existing subscribers is the change of area code. Thus, only area code references, where present for long-distance calling, required updating in directories, letterheads and business cards.

With the proliferation of

area code 718
in the outer boroughs.

Methodology

Most implementations of the overlay method have required ten-digit dialing, by including the area code, for all subscribers for all calling destinations, local or long-distance.[a]

Exceptions

Near numbering plan area boundaries, special situations arose at times when established communities extended on both sides of the boundary. To preserve local community integrity, identity, and convenience, a party could dial an office prefix for a local call with only seven-digits, but the destination was technically located in the adjacent number plan area. If a subscriber called a distant office prefix with the same area code, the call would require the dialing prefix 1 before the seven- or ten-digit number.

A similar practice was implemented on a large scale in the metropolitan area of

area code 703. For most of the second half of the 20th century, it was possible to dial any number in the metro area with just seven digits. The entire area implemented a system of central office code protection in which no central office code was duplicated in the entire area. Each existing central office code was properly routed with each area code in the region so that each telephone number in the region could be dialed with any of the regional area codes, giving the appearance of an overlay plan. One side effect of this scheme was that if a number was in use in any portion of the Washington area, the corresponding number in Maryland or Virginia could only be used in an area considered a safe distance from the metro area, such as western Virginia or the Eastern Shore of Maryland. This system was ended in 1991 due to an impending number shortage on both sides of the Potomac River
.

A similar method was employed in

Gatineau in 2002. That was implemented in a way that the same number could not be duplicated anywhere in eastern Ontario
or western Quebec, even in areas a safe distance from the Ottawa area. However, Canada's inefficient number allocation system and the proliferation of cellphones brought 819 to the brink of exhaustion by the turn of the century. The only available numbers in 819 could have theoretically been used in the former Hull, but they could not be issued without ending seven-digit dialing between Ottawa and Hull. As was the case in Washington, the only way to free up numbers was to end seven-digit dialing in the area, which was done in 2006. The sole legacy of the old system is a "dual dialability" system for federal government numbers on both sides of the provincial border; all federal government offices on the Quebec side duplicated several exchanges worth of their counterparts on the Ontario side.

Rapid growth

tablets), which still require a telephone number for use on cellular networks even if they are unable to make or receive regular calls
.

The rise in popularity of mobile devices has added to the pressure against split plans, as an area-code change affecting the exchange in which a cellphone is based not only forces customers to reprogram their phones but also requires the

updated automatically, there is still the inconvenience of users having to update their contact lists
for local family members or others who have had their numbers changed too.

Compromise

Most overlay plans introduced the inconvenience of mandatory

disadvantage to competitors.[2] In Canada, ten-digit dialing is also a requirement of the Canadian Radio-television and Telecommunications Commission
in overlay area codes.

Popularity

Overlays were initially met with resistance, as they result in multiple area codes in the same geographic area, which requires ten-digit dialing. In many cases, such as

212 in New York City, an overlay was an additional disruption to a community that had already been subject to one or multiple code splits, encountering pushback from state regulators or consumer groups. However, overlay plans were eventually used much more widely in some areas than others. For example, much of Ohio has large overlay complexes, as has northern Georgia and the North Carolina Piedmont. Connecticut, Illinois, Oregon, New Jersey, Massachusetts, Maryland, Pennsylvania, Texas, Virginia and, more recently, California have also implemented many overlays. No area code splits have been performed since 2007, when area code 575 split off 505 in New Mexico
, and no splits are proposed.

Telecommunications companies have increasingly favored overlays even in sparsely-populated rural areas in which ten-digit local numbers are unnecessary, as split plans force cellular providers to reprogram millions of client handsets. Customers also incur costs to publish new letterheads and to reprogram stored address book data on individual devices. Overlays have become more expedient as the proliferation of cell phones has accelerated area codes exhaustion. In most relief planning projects, overlays have become the sole option considered in the planning stage.[3]

This is especially practiced for area codes that have been pushed back to the brink of exhaustion after being recently split, as carriers want to minimize additional customer inconveniences. For example,

area code 410. Within only five years, 410 was already on the brink of exhaustion due to Baltimore's rapid growth and the proliferation of cell phones, pagers, fax machines and dial-up Internet lines. However, the area's dominant telephone provider, Bell Atlantic (now part of Verizon
) realized that a split would have forced residents of either Baltimore or the Eastern Shore to change their numbers for the second time in the 1990s. Accordingly, area code 443 was created as an overlay for all of the eastern portion of Maryland in 1996.

Overlay plans also favor

incumbent wireline carriers over new entrants, as the established firm already has large allocations of numbers in the more desirable existing code, and subscribers of new or growing competing carriers
are relegated to unfamiliar, new codes.

The first example of an area code overlaid on an entire U.S. jurisdiction was

area code 809, the area code for much of the Caribbean, in 1996. A split was deemed unfeasible due to the island's extremely dense population and the lack of a suitable boundary for a split.[citation needed
] Additionally, a split would have forced half of Puerto Ricans to change telephone numbers for the second time in a decade.

The first instance of a statewide overlay was West Virginia's area code 304, in 2009. West Virginia had been served by 304 since the inception of the North American Numbering Plan, but it was obvious by 2007 that the state needed a new area code. At first, state officials voted to split off northern West Virginia with area code 681 and to leave southern West Virginia in 304. However, lobbying by the telecommunications industry led the state to reverse the decision and turn 681 into an overlay. Idaho followed that precedent in 2017 by overlaying area code 208 with 986.

The area codes for four of the five largest Canadian markets (

514 in Montreal, 604 in Vancouver, and 403 in Calgary
) were split in the 1990s. Overlays gained popularity in the Canadian telephone network in the early 2000s. The proliferation of cellphones, fax machines, pagers, and dial-up Internet connections, particularly in larger markets threatened central office code exhaustion in many areas.

Particularly severe allocation problems manifested themselves at the turn of the century in

area code 905 in 1993. While the Golden Horseshoe would have likely needed another area code due to its continued growth, it is very likely that the immediate need for relief would have been staved off had it been possible to reallocate numbers from the smaller rate centers in the region to Metro Toronto. Within two years of the 905 split, 416 was back on the verge of exhaustion. American cities such as New York City, Chicago, and Los Angeles
had been split between two area codes, but that solution was quickly ruled out for Metro Toronto because of the area's extremely dense population and the lack of a suitable boundary for a split. It was ultimately decided to overlay 416 with area code 647 in 2001, two years after Metro Toronto was merged into the "megacity" of Toronto.

The successful implementation of 647 triggered the rapid adoption of overlays across Canada. By 2023, seven-digit dialing had been effectively eliminated nationwide in Canada (as well as in most of the United States), due to both overlays and other regulatory requirements. Overlays are now the preferred method of expansion in Canada, and no numbering plan areas have been split in the country since 1999.

Prairie Provinces
have followed Puerto Rico and West Virginia's lead with province-wide overlays. In those cases, a factor behind the decision was the desire to spare rural areas the expense and burden of changing their numbers.

Types

The

North American Numbering Plan Administrator
recognizes several types of overlays:

In a distributed overlay, or all-services overlay, an entire existing numbering plan area (NPA) gains another area code serving the entire area. As of 2022, all area code overlays are of this kind.

In a single concentrated overlay, only the high-growth portion of an existing area gains a second area code. This was previously implemented in several numbering plan areas, but all of them have since covered entire NPAs.

In a multiple concentrated overlay, the entire existing numbering plan area gains multiple additional area codes, each of which serves a different subsection of the original. This has not been implemented yet.

In a multiple-area distributed overlay, two or more numbering plan areas gain a single new area code covering the entire area, either concurrently or in phases. Examples include

825 in Alberta (over 403 and 780). In a phased example, area code 564 was implemented initially only on area code 360 in 2017, but will expand to three other codes when needed, in western Washington
.

A boundary-extension overlay is a type in which one or more neighboring numbering plan areas (with an overlay code or a primary area code) is expanded. Examples include

623 into a single overlay complex for the Phoenix metropolitan area
.

Service-specific overlays are not practiced in the NANP. Only one case, the first overlay area code in the NANPA, 917, was an example of this. It was established originally as an area code specifically for cellphones and pagers in New York City, but soon afterward, the FCC specified that area codes must not be service-specific, but it grandfathered this use for 917. Later, 917 became available for landline assignments in New York City.

Number pool management

The persistent unpopularity of new area code creation by splits or overlays has contributed to a change in the rules of number block allocation to conserve the pool of available telephone numbers. The change, which allowed for the assignment of smaller number blocks, is commonly known as telephone number pooling, and has slowed the need for new area codes. For example, the western half of Washington, including Seattle, narrowly avoided the need for an overlay in 2001. Area code 564, originally planned for introduction in October 2001, was delayed indefinitely in August 2001 after state regulators determined that the use of number pooling had resulted in more efficiency in the use of telephone numbers in western Washington. The 564 overlay complex was delayed until 2017.

Number pooling is not practiced in Canada. Every competing carrier is issued blocks of 10,000 numbers for every rate center in which it offers service, regardless of its actual subscriber count. Individual rate centers exist even in the smallest hamlets, and even tiny unincorporated villages receive multiple blocks of 10,000 numbers. Larger cities, particularly "megacities" that were created by amalgamations in the 1990s and early 2000s, have multiple rate centers, which were not combined for years, if at all. For example,

disputed – discuss
] of Canada's original numbering plan areas.

See also

Notes

  1. ^ The one notable exception was the introduction of +1-917- overlaying all of New York City; these initially kept seven-digit dial from one +1-212 point to another +1-212, leaving just the overlay numbers as ten digits. In most cases, there is no valid technical reason why a seven-digit local call could not have been sent to the original area code instead of being rejected with an error message; the decision by the FCC and the CRTC to disallow this is a political matter. The presumption is that no one would want the overlay numbers if they were ten digits with the original area code still supporting seven-digit local calling.

References

  1. ^ "NANPA : Numbering Resources - Central Office Codes". nationalnanpa.com. Retrieved October 10, 2019.
  2. ^ FCC. "Area Codes: Frequently Asked Questions". Archived from the original on June 15, 2006. Retrieved June 22, 2006.
  3. ^ North American Numbering Plan Administrator (March 2022). "NANPA 2021 Annual Report" (PDF). Retrieved December 19, 2022.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Overlay_complex&oldid=1193018757"