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Telecom Definitions

Telecom Definitions

The Telecom Industry is guilty of using lots of Acronyms and Terminology that is not always easy to understand if you are not in Telecoms. We try to use plain English and avoid the use of Acronyms and strange Terminology. However sometimes we have to explain Telecom language, so we intend to build here a list of Telecom Definitions – We hope you find it helpful.

PABX – Private Automatic Branch eXchange. Also called PBX

A traditional Telephone System with Physical Equipment on the Customers Premises.

VOIP – Voice Over Internet Protocol.

Telephone Calls that are sent over the Internet instead of a conventional phone line.

Hosted Phone System

A Telephone System, like the old PABX but there is no physical equipment on the Customers premises. The phone system is on the Internet and is looked after by a Telecom Service Provider. It is sometimes refereed to as being in the Cloud.

DDI – Direct Dialing Inwards

These are Private Numbers – one for each extension on a Phone System. The ‘Main’ number may perhaps be answered by a Receptionist who could put a call through to an extension. But you could give out your Private Number (DDI) to say your Friends and Family so they could call you directly without having to go through the receptionist.

POE – Power Over the Ethernet.

Our Phones can be powered either by a small Mains Adapter for each phone or via the Computer Cabling using POE. POE is just an alternative way of powering the phones. It needs a Network Switch that provides POE from the other end of the Computer Cabling.


‘Trunks’ is an American term, here in the UK we call them Phone Lines. You don’t need to know what SIP means (Session ¬†Initiation Protocol) just think SIP Trunks as meaning Phone Lines over the Internet.


Integrated Services Digital Network. A digital phone line service, introduced in 1985 giving clearer speech and 64k data speed. Both have been overtaken by improvements in technology with High Definition Speech of Internet Phones and much faster data speeds with Broadband. As a result ISDN is to be discontinued in 2025.

Internet Phones Yealink T46

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