Central office code protection
In the administration of the
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
Despite its advantages where a community of interest reaches across an NPA boundary, central office code protection was only acceptable as long as it could be continued without the threat of central office code exhaustion in the NPA protecting the code.[1]
Examples
The entire 506-752 prefix is assigned to Aliant Telecom (NB) and serves Campobello Island, New Brunswick.[2] Campobello is a border community[3] and is a local call to Lubec, Maine,[4] in area code 207.
The 207-733 prefix serves Lubec, split between
A seven-digit local call from Campobello to Lubec is possible, provided that 733-XXXX is not assigned to anything in the 506 area code which is local anywhere near Campobello. This may be done in one of two ways:
- The Canadian numbering administrator could mark +1-506-733 as "reserved" and refuse to issue it at all. This was originally the standard procedure.
- The 506-733 prefix could be dumped as far out-of-region as possible within the 506 area code boundary, if calls to the other side of the same code are long-distance and a trunk call within the area code requires the entire number (including the leading 1-506) be dialled. By dumping the 506-733 prefix in Edmundston, the geographically-furthest point still in New Brunswick, the administrator adopts this approach.[6]
Similarly, Edmundston is local to Madawaska, Maine exchanges 207-316, 207-436 and 207-728.[7] The corresponding 506-316, 506-436 and 506-728 prefixes (as of 2014) are not issued by the Canadian Numbering Administrator (CNAC):
- 506,316,,,Available,,Available outside Madawaska: Maine EAS
- 506,436,,,Available,,Available outside Madawaska: Maine EAS
- 506,728,,,Available,,Available outside Madawaska: Maine EAS[8]
A few towns and suburbs on US state boundaries have one central office which serves both sides, using different prefixes in different area codes.[9]
- All South Coffeyville, Oklahoma exchange prefixes are served from Coffeyville, Kansas, population 10000;[10][11] the two are local to each other but long distance to everything else.
- The towns of 508 area code. Ten-digit dialing is now required for calls crossing the area code (and state) boundary.[12]
Limitations
If code protection is implemented by reserving every seven-digit number for a border town in both (or all) of the affected area codes, that community and points in its local calling area occupy numbering resources at double the otherwise-expected rate. This is a minor drawback in small cities with large rural area codes (as the numbers can easily be assignable in distant locations), but can consume numbers rapidly in larger centers such as St. Louis or Kansas City (where such protection must be maintained throughout most or all of the area code region, reducing its lifespan).
In large cities located directly on area code boundaries (such as Ottawa-Hull in
A local calling area spanning three American or Canadian jurisdictions would require any number local to any part of the town to be reserved across all three (or more) area codes. This ultimately led to the breakdown of seven-digit calling between Washington, D.C. and its suburbs in 1991. Since the Washington
Severing the border community from its exhausted home area code using a
See also
- Linked numbering scheme
- 703, Washington DC and MD/VA
- Area code 618, St. Louis/East St. Louis
- Area code 819, Ottawa-Hull
- Area code (three states)
- Area code 816/913, Kansas City
Notes
- ^ The exchange codes in the Providence metro area that were 7-digit dialable from the 508-336 code protection were replicated in the 508 area code from the outset. However, these were located well outside of the 7-digit local calling area for the 336 exchange and required a 1+NXX dialing pattern.
References
- ^ a b AT&T (1980), Notes on the Network, p.2-4
- ^ "Archived copy". Archived from the original on 2014-12-16. Retrieved 2014-12-16.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ "Campobello's sea change". Portland Press Herald. 19 August 2012.
- ^ "Local calling guide: Rate centre information, Campobello".
- ^ "Local calling guide: NPA-NXX search, 207-733".
- ^ "Local calling guide: NPA-NXX search, 506-733".
- ^ "Local calling guide: Rate centre information, Madawaska".
- ^ "Archived copy". Archived from the original on 2014-12-16. Retrieved 2014-12-16.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ "TELECOM Digest OnLine - Sorted: Re: [Crossborder 7-Digit (Dial 1)".
- ^ "Local calling guide: NPA-NXX search".
- ^ "Local calling guide: NPA-NXX search".
- ^ "Local calling guide: NPA-NXX search".