CO Code

This numbering resource is fully administered by the CNA.

CO Code Description

Central Office (CO) Codes, sometimes referred to as NXXs, are the digits D-E-F of the 10-digit North American Numbering Plan (NANP) area address. In the NANP, each digit is identified by an alphabetical character in the order ABC DEF GHIJ. The NANP structure consists of a 3-digit NPA or Area Code (ABC), 3-digit CO Code (DEF) and 4-digit Line Number (GHIJ) in the format NXX NXX XXXX where: N = 2 to 9 and X = 0 to 9. For example:

10-digit Number Format
Examples of uses for CO Codes for which this Guideline applies include Plain Old Telephone Service (POTS), Centrex, Direct Inward Dialling (DID), cellular mobile service, pagers, data lines, facsimile, coin phones and customer owned pay phones.

CO Code Assignment Guideline

The current CRTC-approved Canadian Central Office Code (NXX) Assignment Guideline is available below.  It is available as MS Word documents:

Central Office Code (NXX) Assignment Request and Confirmation Forms

The CO Code Assignment, Reservation, Information Change & Return (Part 1); Routing and Rating Information (Part 2); and In Service (Part 4) forms are part of the Canadian Central Office Code (NXX) Assignment Guideline, which is located in parts on the CRTC website.

Those meeting all the requirements to submit forms related to CO Codes can find direct links to the forms below for submission to the Code Administrator and submit them to

Part 2

During CSCN 60, agreement was reached that iconectiv Telecom Routing Administration (TRA) Part 2 Forms, as developed and amended from time to time by TRA, can be used by Canadian CO Code Holders to facilitate data entry into the TRA database.  The CNA is not required to provide Part 2 Forms of any vintage to any party.

A Job Aid to assist Code Applicants in completing the Part 2 Form may be obtained from TRA. To contact TRA, please see their Contact Us page at:

CO Code Status

The currently assigned CO Codes in Canada are listed here.

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