Inter-Domain Dialing

Domains with Non-Overlapping Extensions

If you have domains with non-overlapping extensions, use the following instructions to configure your interdomain dialing. (DIDs, by nature, are non-overlapping.)


Note: Be sure to place the loopback dial plan entry at the top of the dial plan; however, 911, 411, 611, etc., can be the topmost entries.

  1. For each domain, create a dial plan entry with Try Loopback in the Trunk field.
  2. Enter * for both pattern and replacement.

P.S: Here, "Try loopback" entry is the best and the fastest case scenario because it will look for extension number ( and because it is "non-overlapping" with any other extension number on any other domain) through every domain which exists and make a call to that extension when found.

Domains with Overlapping Extensions

If the extensions between the different domains are overlapping, users will need to dial a prefix before the actual extension number is dialed. For this configuration, you will need to designate a prefix and provide proper pattern and replacement strings. Note: Prefixing simply makes extension numbers non-overlapping; however, prefix-based dialing can be used for both overlapping and non-overlapping extensions.

  1. From the first domain, create a gateway trunk that will be used to dial to the other domain(s).
  2. Create a dial plan entry that uses the gateway trunk just created.
  3. Choose a prefix. Be sure to choose a prefix that doesn’t conflict with your other extensions (i.e., if the domain has extensions beginning with 5, you must use a number other than 5).
  4. For the Pattern field, enter the prefix you’ve chosen followed by a string that corresponds with the number of digits your extensions have. The example shown below is useful for three-digit extensions and will require users to dial a 6 before dialing the extension number (e.g., if the user dials 6400, extension 400 will be called).


  5. For the Replacement field, enter sip:\1@\r;user=phone. (It is not necessary to specify the domain name here. The PBX will use whatever is configured on the trunk.)
  6. Repeat these steps from the other domain(s).
  7. If there is a specific need for dialing between 2 (or more) specific domains, then each (call originating domain's) dial plan's entry's, Replacement field should look like this: sip:\1@destination_domain_name;user=phone

P.S: Here, a special trunk (atleast one) is needed per dial plan entry (between 2 domains) to make sure the call is carried over it everytime an inter-domain call is made.