Configuring a SIP Desk Phone as a Tunnelled External Extension with 3CX Phone System

Note: This post refers to version 12 and older. For v12.5 and later please go here.

Connecting an External Extension to 3CX Phone System is often requested, and can be extremely useful for linking small remote offices and home workers.

Using a phone as a Tunnelled External Extension will require you to have first established a 3CX Tunnel connection to the 3CX Phone System from the Remote Office, by installing, on one of the PCs in the Remote Office, the 3CX SBC (Session Border Controller).

To keep the process simple and flowing it is recommended to start off with a factory reset phone running the latest recommended firmware.

Configuring the 3CX SBC (Session Border Controller)

At the remote site choose a PC that has internet access and download and install the 3CX SBC.

During the installation process you will be prompted to select the network configuration of the 3CX Phone System. Two options are available:

  • 3CX Phone System in installed behind a NAT. In this mode the 3CX Phone System has a Local IP Address and a Public IP Address.
  • 3CX Phone System in NOT behind a NAT. This means that it has one public IP Address.

Next you are required to provide more information about your 3CX Phone System:

  • Provide the Public/External IP or FQDN of the 3CX Phone System. Note that if the FQDN does not resolve the service will not start.
  • Enter the Local/Internal IP Address of the 3CX Phone System.
  • Enter the 3CX PBX SIP Port (Default 5060).
  • Enter the 3CX Tunnel Port (Default 5090).
  • Set a Name for this connection.
  • Enter the 3CX Tunnel Password which can be found in the 3CX Management Console under “Settings” > “Network” > “3CX Tunnel” tab.

Complete the installation procedure. The 3CX SBC will run as a service on this machine.

3CX SBC PnP

Phones that are plugged in the remote network should appear in the 3CX Management Console.

Configuring a Cisco (or Linksys) SPA as a Tunnelled External Extension

To configure a Cisco SPA as a Tunnelled External Extension, you will need to start as if configuring for a LAN Extension, then do the following:

  • In the “Ext1″ page, go to the “Proxy and Registration” section, and set:
    • “Proxy” field to PRIVATE IP Address and SIP listening port of the 3CX PhoneSystem machine (in this example 10.0.0.11:5060)
    • “Outbound Proxy” field to PRIVATE IP Address and SIP listening port of the 3CX SIP Proxy Manager machine (in this example 192.168.0.2:5080)
    • “Use Outbound Proxy” field to “yes”.
    • “Use OB Proxy In Dialog” field to “yes”.

Configuring a Polycom SoundPoint / SoundStation as a Tunnelled External Extension

To configure a Polycom SoundPoint / SoundStation as a Tunnelled External Extension, you will need to start as if configuring for a LAN Extension, then do the following:

  • Go to the “SIP” page
  • In the “Server 1″ section, set:
    • “Address” field to the PRIVATE IP Address of the 3CX Phone System machine (in this example 10.0.0.11).
    • “Port” field to the SIP listening port of the 3CX PhoneSystem machine (in this example 5060).
  • In the “Outbound Proxy” section, set:
    • “Address” field to the PRIVATE IP Address of the 3CX SIP Proxy Manager machine (in this example 192.168.0.2).
    • “Port” field to the SIP listening port of the 3CX SIP Proxy Manager machine (in this example 5080).

NOTE: If a user of a Polycom phone configured behind the 3CX Sip Proxy Manager initiates a call, and presses the  HOLD button, the call cannot be resumed and audio will be lost. This is because of an issue in the way the Polycom phone generates proxy authentication information when it uses outbound proxies.

Configuring a Snom as a Tunnelled External Extension

To configure a Snom as a Tunnelled External Extension, you will need to start as if configuring for a LAN Extension, then do the following:

  • Go to the “Identity 1″ page, and in the “Login” tab, set:
    • “Registrar” field to the PRIVATE IP Address of the 3CX Phone System machine (in this example 10.0.0.11:5060).
    • “Outbound Proxy” field to the PRIVATE IP Address and SIP listening port of the 3CX SIP Proxy Manager machine (in this example 192.168.0.2:5080).

Configuring a Yealink as a Tunnelled External Extension

To configure a Yealink as a Tunnelled External Extension, you will need to start as if configuring for a LAN Extension, then do the following:

  • In the “Account” page, select “Account 1″.
  • Go to the “Basic” section and set:
    • “SIP Server” field to the PRIVATE IP Address of the 3CX Phone System machine (in this example 10.0.0.11).
    • SIP Server “Port” field to the SIP listening port of the 3CX Phone System machine (in this example 5060).
    • “Enable Outbound Proxy Server” field to “Enabled”.
    • “Outbound Proxy Server” field to the PRIVATE IP Address of the 3CX SIP Proxy Manager machine (in this example 192.168.0.2).
    • Outbound Proxy Server “Port” field to the SIP listening port of the 3CX SIP Proxy Manager machine (in this example 5080).

External Extensions – Summary Table

Brand STUN RPort Direct Mode Tunnel Mode
Aastra YES YES YES NO
Cisco YES YES YES YES
Linksys YES YES YES YES
Polycom NO NO NO YES
Snom YES YES YES YES
Yealink YES YES YES YES

Note: While not officially supported, there are cases where it is possible to work without the Tunnel. The configuration of such setups can be found here.

Liked this article?


Get notified of new articles
or share
You might also be interested in:
  1. Pingback: Voip Alarm Relay : Annuncicom-100 | Guide to Home System Security