The ABCs of business telephony

November 17th 2016

The ABCs of business telephony

It’s easy to feel swamped by acronyms when talking to business telephony representatives, even more so with telecommunications technicians – PRI, PBX, IP PBX, PABX, SIP, IP, VoIP, LAN, VLAN – it goes on and on.

As you try to process the different solutions offered, do you ever wonder what the acronyms mean?

Are they still talking about my phone system?

Here’s a short example of a fictitious organization to help explain the main acronyms used in telephony.

We’ll look at a growing SME with 60 employees in two different locations that wants to improve and facilitate internal and external communications.


The main role of a PBX (Private Branch Exchange) or PABX (Private Automatic Branch Exchange) is to link the telephones within an institution to the PSTN (public switched telephone network) used by different providers of telephony services.

The PBX is the heart of your telephony solution because it performs the following tasks:

1) distributes incoming phone calls to the correct extension

2) authorizes outgoing calls to the PSTN

3) manages internal calls between various extensions

4) manages other features, such as fax and voice mail

Consider the case of the fictitious company with 60 employees, each with their own telephone extension, making and receiving many calls.

Without a PBX, the company would need up to 60 different telephone lines to link each of the phones to the public telephone network and support their activities.

Each of the employees would have their own number, and calls from one employee to another would be considered outside calls.

In addition to being extremely costly, the solution wouldn’t work well for the organization.

The installation of a PBX in each branch would allow the company to reduce the number of lines from 60 to about 20 to support all of its activities.

The PBX allows the sharing of lines between various users. We suggest one line per three or four employees, depending on the nature of the activities in the company. The PBX also manages internal calls between different telephones.

IP PBX and Hybrid PBX offer the same features as PBX, but they include IP (Internet Protocol) in addition to traditional (analogue) phone solutions. Most PBX systems on the market today are Hybrid PBX, capable of supporting both technologies.


PRI (Primary Rate Interface) is a line that includes up to 23 channels and allows several calls to be made at the same time. The PRI line connects to the PBX like a traditional analog line.

If we go back to our fictitious company, using a PRI line would enable it to save substantially in monthly payments – one PRI line costs less than 20 individual lines.

Through its two PBX systems, the company could connect its two sites on the same PRI line by creating a VPN (Virtual Private Network), which would fully integrate internal communications between one branch and the other, despite the physical distance separating them.

The PRI line becomes an economical choice when the company has a high call rate and more than 15 lines are required. 


SIP lines (Session Initiation Protocol) or SIP trunking use IP (Internet Protocol) technology and replace traditional analog lines or the PRI line. With an SIP line, all calls take place through the Internet, no longer going through the PSTN (public switched telephone network).

In order to have access to SIP technology, companies must have an IP PBX or an SIP gateway, a technology offered by some specialized providers.

The main advantages of SIP lines are the savings and the possibilities for developing a unified communications strategy.


Don’t hesitate to ask your representative or telecommunications technician to simplify their presentation by avoiding these acronyms. After all, the discussion should be focussed on your communication needs and the best solution to meet them.