Central Office Code (NXX) Assignment Guidelines (COCAG)
|Publication Date:||1 August 2018|
Purpose and Scope of This Document
This document specifies guidelines for the assignment of central office codes (also referred to as CO codes in this document). The term CO code or NXX refers to sub-NPA destination codes for addressing. Sub-NPA refers to digits D-E-F of a 10-digit NANP area address, e.g., 740 is the CO code (NXX) in (201) 740-1111. Examples of uses for CO codes (NXX) for which these guidelines apply include plain old telephone service (POTS), Centrex, Direct Inward Dialing (DID), Commercial Mobile Radio Service (CMRS), data lines, facsimile, coin phones, and customer owned pay phones. While these guidelines were developed at the direction of the FCC,1 they do not supersede controlling appropriate NANP area governmental or regulatory principles, guidelines and requirements. These industry consensus guidelines are expected to apply throughout the NANP area subject to guidelines and constraints of the NANP area administrations unless the affected administrations direct otherwise.2
These guidelines apply only to the assignment of CO codes (NXX) within geographic numbering plan areas (NPAs). This does not preclude a future effort to address nongeographic NPAs in the same guidelines.3 CO codes (NXXs) are assigned for use at a Switching Entity or Point of Interconnection they own or control. Entities assigned CO Codes are termed "code holders." While the ultimate delivery of any call to a CO code (NXX) need not be geographically identified, by necessity initial routing is geographically defined. Therefore, for assignment and routing purposes, the CO code (NXX) is normally associated with a specific geographic location within an NPA, from which it is assigned. For some companies this is also used for billing purposes.
1 This effort has been undertaken at the direction of the Federal Communications Commission (FCC), in a letter to NANPA dated June 21, 1991, in an attempt to develop procedures that can be applied uniformly while using a finite numbering resource in the most efficient and effective manner possible and subsequently changed per the FCC's Numbering Resource Optimization orders under Dockets 99-200, 96-98 and 95-116.
2 The Canadian Radio-television and Telecommunications Commission (CRTC) has approved the Canadian Central Office Code (NXX) Assignment Guidelines for the administration of Central Office Codes within Canadian Numbering Plan Areas (NPAs) by the Canadian Numbering Administrator (CNA). See www.cnac.ca.
3 Separate procedures apply to the assignment of NXX codes within currently assigned Service Access Codes (SACs), and others will be developed, as appropriate, as new SACs are assigned by NANPA. For example, NXX assignment guidelines for the 900 SACs are available. Separate guidelines also will be prepared to address the assignment of numbering resources reserved for non-geographic applications.