About PBX

Below we’re about to take a closer look at PBX and figure out what it actually is and how it works. But first, a little background story!

PBX stands for private brand exchange and is also called subscriber PBX. It’s a PBX for authorities and companies and isn’t as of yet available for the general public. A PBX can have various connections as well as mains (also called central mains). The connection goes through internet or ISDN.

Subscriber PBX can be divided into two categories – manual and automatic. Modern automatic PBXs consist of software. The manual PBX is going out of fashion, at least in Sweden. The faster development goes the more automized society will become. How PBXs will look in the future is hard to predict.

  • The acronym PBX stands for private branch exchange.
  • It’s a telephone PBX for for companies and authorities.
  • It can be divided into two categories; automatic and manual.
  • Up until the 1980s, Televerket has monopoly on PBX.
  • The connection in a PBX goes through internet or ISDN.
  • PBX is also called subscriber PBX and comes in diffrent sizes.
  • The PBX MD110 was a huge export success for Ericsson.

What is PBX?

PBX (private branch exchange), also called subscriber PBX, is a telephony PBX within a company that isn’t public. This sort of PBX has both internal and external lines where the internal are called extensions and the external are called central circuit or main circuit. These main circuits were preciously analogue phone lines.

In today’s modern society the connection goes through internet telephony or ISDN to superior station. ISDN, APNSS, QSIG or DPNSS are used methods for communication between subscriber PBXs that are located in certain locations. These PBXs come in many sizes, from calling to main circuits or three extensions to hundreds of main circuits and 10 000 extensions.

´Subscriber PBXs is named after the many extensions and their main circuits, for example Tellus 15 (with 15 extensions). They can further be divided into the categories; automatic and manual. Nowadays the automatic PBX can consist of only software. A manual PBX instead has thread PBX or plug PBX.

PBX in Sweden

It may come as a surprise that Televerket had monopoly on PBX up until the 1980s. Companies and authorities had to rent their PBXs, which could have been a huge investment for them. A company PBX for a large company could cost as much as 5 million Swedish kronor.

 During the 1980s and 1990s the old and big electromagnetic PBXs were discontinued. They were replaced with program memory steered PBXs that were then called “electronic PBXs”. The first non Swedish developed PBX that was used was A345 (the Canada PBX). The PBX was built by the Canadian Northern Telecom and was adjusted for Swedish standards.

The PBX MD110 was jointly developed by Ericsson and Televerket. This PBX could be extended to a vast amount of extensions and came to be a huge export success for Ericsson. Volume wise, the MD110 became one of the biggest subscriber PBXs in the world. Ericsson exported these for a whole 3-4 billion per year in the beginning of the 1990s.