In
telephony, especially in
North America, an
overlay plan is the
practice of introducing a new
area code by
applying it onto a
geographic area that is
already occupied by one or more existing area codes, resulting in
two (or more) area codes serving the same area.
Methodology
Prior to the introduction of overlay plans, the method of
introducing new area codes, known as
numbering plan areas (NPAs), in a region
was to divide the existing area of one NPA into two (or more)
pieces, allowing the more established or developed section to
retain the original NPA, and changing the numbering space of the
other section(s) to have a new NPA.
For example, the original NPA for the
entire state of Washington
was 206; today 206
applies to only the city of Seattle
and
immediate vicinity. This practice became known as a
split plan.
Rapid growth
Urban sprawl accelerated the rate of
expansion of metropolitan areas, and multiple split plans have
caused the geographical area of NPAs in those areas to shrink.
Also, the rapid growth in popularity of
mobile phones, in addition to regular
land line growth, has increased demand for new
phone numbers even more. The practice of instituting an area code
split has become much more costly because of various business or
administrative inconveniences to customers, such as changes in
stationery,
advertising, and otherwise communicating and
remembering the number change among friends and customers.
The rise in popularity of mobile phones has added to the pressure
against split plans, as a NPA change affecting the exchange in
which a cell phone is based requires the wireless carrier to
reassign the number of every device based in those areas.
Reluctant solution
To alleviate complaints about such changes, in the late 1990s, the
telecommunication industry began to introduce "overlay plans" as a
means to introduce new NPAs. In this model, one fixed geographic
area would concurrently have multiple valid NPAs throughout. This
plan's main benefit, which addressed many of the issues causing
resistance to split plans, was that all existing
phone numbers remained unaffected by the new
NPA. Newly-assigned numbers in the overlay plan areas would have
the new area code. As a result, two telephones, located next to
each other in the same building or house, could have different area
codes.
Compromise
However, overlay plans introduced a new inconvenience: mandatory
10-digit dialing (i.e. the area
code must be included), even for
local
calls, in the affected area. This and the difficulty of
remembering all the area codes in a geographic area made overlay
plans only marginally less unpopular than split plans. It should be
noted that 10-digit dialing is not a technical requirement but an
FCC mandate to promote fairness among telephone companies.
Popularity
Overlay plans have been used much more widely in some areas than
others. For example, the northern third of
Ohio is covered by two large overlay
complexes, as is northern
Georgia.
New Jersey,
Massachusetts, and
Maryland have also used overlays
heavily, and are completely or almost completely overlaid. In
California, about one
third of the state, mostly in the southern California is overlaid,
despite the many splits that have resulted in tiny divisions.
Overlays have also generally been more popular in Canada, with all
of
British
Columbia and
Alberta
and large portions of
Ontario and
Quebec overlaid by the end of
2008.
Types of overlays
The
NANPA recognizes different forms of
overlays:
- Distributed overlay - in which an entire existing NPA gains
another NPA serving the entire area
- Single concentrated overlay - in which only the high-growth
portion of an existing NPA gains a second NPA
- Multiple concentrated overlay - in which the entire existing
NPA gains multiple additional NPAs, each of which serves a
different subsection of the original NPA.
Some overlay plans not fitting the above forms have been noted:
- Two or more existing NPAs collectively gain a single overlay
NPA covering the entire area. Washington's planned 564 would have fit this description, as would
the plans to introduce 587 in Alberta
and expand
778
in British Columbia
from a concentrated overlay of 604
to
simultaneously overlay 604 and 250
- A NPA is extended to overlay on top of a neighboring NPA.
Florida's 321 was overlaid in this way
onto 407, from which it had originally
split.
Number pool management
The persistent unpopularity of new NPA creation, whether by split
or overlay plans, led to a change in the rules of number block
allocation, in order to conserve the pool of available phone
numbers. This change, which allowed for the assignment of smaller
number blocks, is commonly known as
number pooling. This has noticeably slowed
the need for NPA growth, but not completely. For example, the
Western Washington area narrowly
avoided needing an overlay NPA in 2001.
Area code 564, originally planned for
introduction in October 2001, was canceled in August 2001 after
state regulators determined that the existing number pool had begun
to be used more efficiently.
See also
References
- LincMad - Forms of NPA Relief
External links
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