How to set up a PBX line between two LANCOM VoIP routers and enable internal calls between subscribers at different ends.



The first important step is to think about the internal dialing plan for both ends.

In our example, both ends use three-digit internal extension numbers.
  • On Router 1, they all start with 1, i.e. 1xx.
  • On Router 2, they all start with 2, i.e. 2xx.

It helps with the structured setup of the call routing if the numbers at each end of the line have a different first digit.

1) Setting up DNS forwarding for the SIP domain at the remote site

1.1 In LANconfig, open the configuration of the LANCOM VoIP router and go to the menu Configuration -> IPv4 -> DNS -> Forwarding.

1.2 Click on Add and enter the domain *.domain.remote, where * is a placeholder which ensures that all requests are forwarded to the domain on the remote VPN gateway.

1.3 Set the remote site with the local IP address as used by the DNS server at the remote site. This may be the LANCOM at the remote site or a different local DNS server. If you operate a different local DNS server, this must be informed of the VoIP domain.

2) Creating the PBX lines on the two devices

2.1 Change to the menu VoIP Call Manager -> Lines -> SIP PBX lines.

2.2 Configure the values ​​for the PBX at the remote site. The SIP domain is the domain at the remote site, i.e. of the other router.

3) Setting up the call routing

3.1 Change to the menu VoIP Call Manager -> Call router -> Call routing -> Add.

It is important to set a high priority here, so that the routing entry acts before any others. The entry 2# for the destination number and the mapped number causes any dialed number that begins with 2 to be routed to the PBX line ROUTER2 in our example.

If the line is not available at that moment, the call is diverted via ISDN to the landline number of the remote site.

This appears as follows in the call-routing table: