How 3CX Works

An understanding of the overall structure of a 3CX phone system will help you understand what’s needed for a versatile VoIP phone network.

3CX desk phone and mobile app

3CX phone system

The 3CX phone system is a server-based software PBX that can manage calls and uses VoIP to carry voice signals. It runs on a Windows Server that can be located on your premises or hosted in the Cloud.

Your external calls will either be routed through VoIP gateways connected to your existing phone lines, or through your internet connection using VoIP.

3CX phone system diagram how it works

A guide to terminology

Internet connection

3CX Internet connectionAn Internet connection is necessary for VoIP communication with remote softphones, smartphones and other offices you may have. This connection can be via broadband or leased line for example. Having a reliable Internet connection is critical here, but it can save you money with lower call costs.


“Internet Protocol” a way of transporting data over physical network cabling or wireless.

IP Phones and handsets

IP PhonesThese are physical phones that work digitally using VoIP.

They can share your data infrastructure (wireless or cabled) with computing devices rather than needing a dedicated phone wiring system in your building.


A “Private Branch Exchange” – the heart of a phone system – allows you to have phone extensions and make internal calls at no cost.

PSTN network

PSTN network - 3CX phone system“Public Switched Telephone Network” – the traditional phone network running over landlines, mobile networks and so on.

It doesn’t use VoIP to carry the voice signal: it is analogue


“Session Initiation Protocol” – essentially a virtual telephone line that runs over IP networks (including the Internet). As an element of a complete 3CX phone system, it’s an alternative to a VoIP/PSTN Gateway

Smartphones with App

3CX smartphone AppsUsing an app though they can also make calls via the 3CX phone system, saving money and allowing your extension to travel with you anywhere that you have an Internet connection.


3CX SoftphoneA piece of software running on a computer which interacts with the phone system, and with your physical handset.

It also interacts with other software on the computer (such as with your Outlook Contacts, so you can click to call, for example).


A voice signal can travel in two ways:

  • As an analogue signal over traditional phone lines and the PSTN, or
  • Digitally encoded over an IP network. VoIP uses the latter.

VoIP / PSTN Gateway

VoIP GatewayIt’s not always possible for a voice signal to reach its final destination using VoIP alone (not everyone has a VoIP phone system yet).

A VoIP Gateway “translates” the voice signal from VoIP to analogue and vice versa. This means that your 3CX phone system can make and receive calls to the entire phone network.

Signals and protocols

Starting from the top, we can see that VoIP runs over IP, and this travels across some sort of digital data network.

VoIP will pass through a VoIP Gateway, or via a SIP provider, in order to allow the voice signal to travel over traditional landlines or the PSTN.

Learn more about 3CX

Find out more about 3CX and why this should be your phone system of choice.