3CX Phone can be configured to connect to 3CX PhoneSystem from the same LAN, and also from a remote location. If 3CX Phone is going to be used from a remote location, you can also take advantage of the built-in tunnel functionality to overcome NAT traversal issues, allowing you work from virtually any remote location.

3CX Phone has STUN settings pre-configured, but it is smart enough to know that it only needs to use STUN if is set up as a remote extension in Direct Mode. The STUN settings will not be employed if the phone is configured to work as a Local extension or as a Remote Extension with the Tunnel Protocol.

The “Credentials” section of the configuration screen will always contain the same information, regardless of whether the phone is going to be used locally, or from a remote location, or using the built-in tunnel – simply provide the Extension Number, the Authentication ID, and the Authentication password in the appropriate fields.

3CX Phone in the same LAN as the PBX

This is the simplest configuration. Select the radio button labelled “I am in the office – local IP”, and enter the local IP Address of the 3CX PhoneSystem machine.

3CX Phone from a Remote Location – Direct Mode

Configuring 3CX PhoneSystem to work from a Remote Location in Direct Mode (without using the built-in tunnel) is also straightforward. Select the radio button labelled “I am out of the office – external IP”, and enter the public IP Address of the 3CX PhoneSystem machine.

With the phone located in a remote location, it is largely dependent on the remote location’s WAN-to-LAN device performing NAT correctly.

Sometimes, the internet connection available may not be able to provide correct NAT functionality, either because the WAN-to-LAN device does not implement it correctly, or because the connection implements multiple NAT layers (double-NAT), or because SIP and/or RTP traffic is detected and intentionally blocked. If you need to overcome such issues, this will bring you to…

3CX Phone from a Remote Location – Tunnel Mode

3CX Phone provide a built-in tunnel client which connects to the tunnel “server” implemented directly within 3CX PhoneSystem.

The Tunnel Server listens for incoming connections on the 3CX PhoneSystem machine on port 5090 in both UDP and TCP. Configuration on the Server side is straightforward – you need to implement port forwarding on the WAN-to-LAN device between 3CX PhoneSystem and the Internet so that any traffic received by the WAN-to-LAN device on the WAN Interface to the public IP Address to port 5090 will be forwarded inside the LAN to the 3CX PhoneSystem machine’s local IP Address.

The Tunnel Client will first attempt to connect to the UDP listener on the 3CX PhoneSystem machine (since it is better suited to real-time traffic such as RTP). If this fails because of residual NAT traversal issues, it will fall back to using TCP instead. Since TCP is connection-based, you are practically assured of a successful connection unless port forwarding on the server side is not correctly set up, or unless the traffic is actively being blocked.

Configuring 3CX PhoneSystem to work from a Remote Location in Tunnel Mode is also straightforward. Select the radio button labelled “I am out of the office – external IP”, and enter the public IP Address of the 3CX PhoneSystem machine. Next, enable the “Use 3CX Tunnel” checkbox, enter the 3CX PhoneSystem machine’s local IP Address inside its own LAN, and provide the 3CX Tunnel password and port (default 5090) as configured on 3CX PhoneSystem (which is set from the 3CX Management Console by going to the “Settings -> Network” Settings page, under the “3CX Tunnel” tab).

Multiple Sound Devices

It’s easy to be fooled into thinking there’s a sound issue when you have multiple sound devices on your machine – sometimes you may not even be aware of this. Windows Vista and Windows 7 are now “smart” and can detect when a headset and/or microphone is plugged into the machine, and creates an additional “virtual” sound device to the operating system for the headset/microphone. Some people also use USB phones – which are in fact little more than an additional Sound Device connected to the PC via the USB port.

Correct configuration of the Microphone and Speaker device settings will resolve most issues related to missing audio.