Connecting an External Extension to 3CX PhoneSystem is often requested, and can be extremely useful for linking small remote offices and home workers. Here we get a shot at using other phones as External Extensions.

Using …

Skills Covered by this Module

What is SIP
What is RTP
How calls are setup using SIP Message exchanges

TFTP stands for Trivial File Transfer Protocol simply because of its simplicity.  It is mainly used for automated file transfers between machines on UDP Port 69.  In a VoIP environment TFTP is used to upload …

This guide has been tested for RelayFax 7.0.
Be aware that previous versions CANNOT work with 3CX PhoneSystem. Note also that more recent versions may have different interface formats and functionality.

If you need a simple, SIP-based door phone, the Robin Compact SIP C01040 and C01041 provide a simple and inexpensive solution. This document will explain the steps necessary to set up, configure, and test one …

This document will provide an overview of the more common concepts which need to be kept in mind when configuring 3CX PhoneSystem inside your network infrastructure, including the following topics:

NAT Configuration
STUN Resolution
DNS Resolution in a …

Skills Covered by this Module

Preparing an Extension for Provisioning
Advantages of Provisioning through 3CX Management Console
The different types of provisioning and what phones they work with
Automatic Provisioning using DHCP Option 66

Relevant Course Materials

Adjusting The Built-In Phone …

In order for 3CX Phone System to communicate successfully with VoIP providers and Remote Extensions, your firewall/router device must be configured for SIP operation. To maximize your chances of success, make sure you choose a …

This article explains the main fields included in a SIP INVITE, which is sent to set-up a VoIP call. A SIP INVITE message contains typically between 4 and 6 header entries with contact information inside …

All SIP Phone calls consist of 2 channels:

Messaging – SIP
Media – RTP

Messaging is carried using UDP or TCP (normally UDP) SIP packets – It is used for device registration, call setup/teardown, on-hold notification, call …

This is a complete guide that will provide detailed information on how to:
1. Setup 3CX Phone System with Secure SiP (TLS) (In this way the SiP messaging will be encrypted and therefore more …

Note 1: The results generated from these tests should remain valid while the VoIP Provider keeps your account settings static. If your VoIP Provider account is reconfigured, it may be necessary to redo these …

The following is a complete list of ports that 3CX PhoneSystem uses in a default installation scenario:

TCP:80
…
If 3CX is installed for IIS, this is the default port number to reach the 3CX Management Console (http://<ip_of_pbx>/management) …

How does direct SIP work?
The way direct SIP calls are initiated is very similar to the way sending an email works. A caller can call a callee from either a stand alone SIP phone which …

When a SIP based VoIP call is established, the audio or video sent between two SIP entities or more is streamed. Since many different codecs are supported by different devices or software, and each individual …

When media is streamed in a SIP based voice over IP call, being audio, or video or both, one of the requirements is for the participants to know the media details, i.e. transport address, transport …

Busy Lamp Field (BLF) is a light on an IP phone which tells you whether another extension connected to the same PBX is busy or not. This has to be configured manually from the phone …

Five Questions to Help You Decide Which Telephone System Is Best for Your Business
There are various options in the market nowadays when it comes to business telephone systems; therefore it can be a challenge to …

As seen in Part 1 of this article, STUN enables a SIP entity running behind a NAT to discover its public IP and what type of NAT is running on the gateway it is connected …

I want to start off by giving credit on this nice little piece of engineering to Worksighted systems engineer Matt Scott.
I want to start off by defining a remote extension as one that must exit …

Busy Lamp fields are the LEDS on phones that indicate the status of other extensions.  BLF fields have been “inherited” from old style PBXs that have this feature.
Nowadays, presence information is also displayed via 3CX …

This nugget shows how to setup an external extension using direct SIP.
Using the VoIP client as an example it walks you through the process of configuring extensions that reside outside your LAN.

NAT & Firewalls typically present some challenges to VoIP, however with a good understanding of what’s happening it’s possible to make VoIP calls work easily. And being able to have external extensions and bridges …

This video is a high level overview to SIP & RTP – explains the basics of the protocols in a 4 minute video

This video explains how to interpret the 3CX Phone System server status logs. This video walks you through the setup and tear down of a phone call, explaining the messages that are generated along the …