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CRTC Universal Call Blocking – How it Could Impact Your Organization

Eric Losier

On December 19th 2019, all Canadian carriers will have to comply with a new CRTC policy for the “universal blocking of calls with blatantly illegitimate caller identification.” The objective of this policy is to protect the public against unwanted, unsolicited, and illegitimate telecommunications. Since many such calls often display an invalid caller ID, the CRTC expects this measure to at least reduce the number of SPAM calls, although it is clear they will not be completely eliminated.

In order to comply with this new policy, carriers will now implement blocking rules at the network level for calls where the originator (calling party) presents an invalid caller ID (CLID), such as:

  • CLID matching the telephone number of the person being called (mirroring).
  • CLID not conforming with the North American Number Plan (NANP), for example:
    • Invalid area codes: cannot start with 0 or 1, or end with 11.
      • 000-000-0000, 123-456-6789, 511-345-7890
    • Less than 10 digits: 1234, 456-7890
    • Invalid subscriber number: following the area code, the subscriber number cannot start with 0 or 1.
      • 514-012-3456
    • CLID not conforming with the E.164 International Numbering Plan:
      • More than 15 digits: +33-44-55-678901234567

Business Impacts

In order to avoid outbound calls being blocked by your carrier, it is important that your Cisco Unified Communications Manager (CUCM) and PSTN gateways always be configured to send a conforming Caller ID. Specifically, sending an internal Directory Number as the CLID for an outbound PSTN call will unequivocally result in a rejected call. 

Ideally, a thorough review of dial plan rules, including an analysis of the configuration of every Directory Number, should be performed right away to make sure your business continues to run without skipping a beat. As a temporary measure, default CLID presentation rules at the PSTN gateway level can also be implemented, trapping calls with non-conforming CLIDs and modifying them “on the fly” to a default valid value.

Our team of UC experts at Stack8 can help with making sure your Cisco UC environment is ready for this critical change. Get in touch today!

November 27, 2019

Eric Losier