CO Code

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| CO Code Description | CO Code Assignment Guideline | CO Code Assignment Request & Confirmation Forms | CO Code Status | | CO Thousands-Block Status |

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:

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.

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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 assignment practices (CRTC staff letter dated June 01, 2010)
• Canadian Thousands-Block (NXX-X) and Central Office Code (NXX) Assignment Guideline (Canadian TBCOCAG), Version 1.0, dated 16 June 2026
• Appendix A - Audits
• Appendix B - Months-to-Exhaust Certification Worksheet
• Appendix C - Time Lines
• Appendix D - Plant Test Code Application and CNA Response/Confirmation Form
• Appendix E - Location Routing Number (LRN) Assignment Criteria
• Appendix F - Aging and Administration of Disconnected Telephone Numbers
• Appendix G - Reserved and Held Telephone Numbers
• Appendix H - Special Administrative Measures with respect to Code
• Appendix I - Confirmation of Pooled CO Code Activation in the PSTN (CAPSTN) Form Holders that cease Business Operations

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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 COCodeApps@cnac.ca.

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CO Code Status

The currently assigned CO Codes in Canada are listed here.

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CO Thousands-Block Status

The currently assigned CO Thousands-Blocks in Canada are listed here.

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