Central office code protection

In the administration of the <a href="/facts/North_American_Numbering_Plan/0QQ8v3ph">North American Numbering Plan</a>, central office code protection is a numbering policy for maintaining local <a href="/facts/Seven-digit_dialing/w4RUKy6J">seven-digit dialing</a> in communities that extend on both sides of the boundary line between multiple <a href="/facts/Numbering_plan_area/0QQ8v3ph">numbering plan areas</a> (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 <a href="/facts/Competitive_local_exchange_carrier/tzF93Bcj">competitive local exchange carriers</a> has caused depletion of available number prefixes, often requiring <a href="/facts/Ten-digit_dialing/22AY5qgI">ten-digit local calls</a> and <a href="/facts/Overlay_plan/faRNxFIj">overlay plans</a> 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.

Central office code protection open-in-new

Central office code protection