In the administration of the North American Numbering Plan, central office code protection is a numbering policy for maintaining local seven-digit dialing in communities that extend on both sides of the boundary line between multiple numbering plan areas (NPAs), such as in cross-border towns on state lines. Code protection prevents the use of the same telephone number on both sides by not assigning the same central office code of one NPA in the adjacent NPA. 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 where multiple area codes serve the same geographic location. 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. Examples The entire 506-752 prefix is assigned to Aliant Telecom (NB) and serves Campobello Island, New Brunswick. Campobello is a border community and is a local call to Lubec, Maine, in area code 207. The 207-733 prefix serves Lubec, split between FairPoint Communications and a pair of competitors using number pooling. Both area code 506 and 207 use seven digits for local calls. 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. Similarly, Edmundston is local to Madawaska, Maine exchanges 207-316, 207-436 and 207-728. 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