For a E.164 dial plan where routes exist for +! to the PSTN the following is required:

  1. The Service Param (Call Manager) Automated Alternate Routing set to TRUE
  2. A single AAR group created with prefixes left as default
  3. Each DN Line Appearance should have one of the following set for AAR to use to reach the phone/line;
    1. External Phone Number Mask
    2. AAR Destination Mask
  4. The DN must have the AAR Group set to AAR group created in Step 2.
  5. Either in the DP or the Device Settings:
    1. DP – Device Mobility Related Information
      1. AAR Calling Search Space
      2. AAR Group
    2. Device – Device Information
      1. AAR Calling Search Space
      2. AAR Group

Alternatively where Route Groups and +! global routes don’t exist then the AAR Group will need configuring with prefixes for other AAR groups. Each AAR group is assigned to a Device Pool (or Device or DN) this AAR Group will provide the required prefix to prepend to the dialled number in order for it to be routed to the PSTN. i.e. access and trunk code and E.164 DDI prefix e.g. “9 0 1245 821” which prefixed to the dialled number i.e. 8302222


Summary of Two Sides of Configuration

When Phone A calls DN on Phone B and CAC prevents to call on-net then the following must be configured for AAR to work from Phone A to DN on Phone B with PSTN.
  1. Configure the Device (Phone A) (or Device Pool) AAR Group & AAR CSS settings to allow the calling phone to use ARR. AAR group provides prefix if required for the destination group as specified in the called DN configuration. AAR CSS provides the typical calling permissions.
  2. Configure the Directory Number with ARR Group and AAR Mask (or External Mask) to enable the calling device (Phone A) to call this DN via the PSTN (using E.164) using AAR when E-CAC prevents on-net calling. The AAR Mask will provide the required E.164 numbers to dial. Prefixing this with the prefix provided in the AAR group matrix for Calling and Called groups to the AAR mask will provide the full CUCM PSTN routable E.164 plus access/trunk codes to call the number externally.
For the reverse call to happen, the same setup is required for the other direction.

Simon Birtles

I have been in the IT sector for over 20 years with a primary focus on solutions around networking architecture & design in Data Center and WAN. I have held two CCIEs (#20221) for over 12 years with many retired certifications with Cisco and Microsoft. I have worked in demanding and critical sectors such as finance, insurance, health care and government providing solutions for architecture, design and problem analysis. I have been coding for as long as I can remember in C/C++ and Python (for most things nowadays). Locations that I work without additional paperwork (incl. post Brexit) are the UK and the EU including Germany, Netherlands, Spain and Belgium.