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What is PBX?


A PBX system - standing for Private Branch Exchange - is a telephone network owned and operated by an enterprise rather than by a telephone company. Technically, the telephone company connects to the enterprise, providing access to the “outside world”, and the private branch exchange system manages connections, extensions and communications within the enterprise. All operations are now usually done automatically, without the need for a human operator to assign incoming or outgoing calls to correspondents.


Originally developed as analogue networks, these systems may now use digital technologies and allow Voice Over IP calls, with conversion to and from analogue signals enabled to communicate with the “plain old telephone system” for other calls which may need it.

Furthermore, these systems may now be totally hosted (“virtual” systems), requiring no hardware installation.


Variations therefore include:

- IP PBX, hosted or not hosted,

- PBX systems, hosted or not hosted.


These systems include:

- Telephone lines (called “trunks”) connected with the system’s core;

- A computer in charge of switching calls within the enterprise network and outside it;

- Physical lines within the enterprise network;

- A console or switchboard used by an operator to setup the system may be added.


Alternative systems include:

- “Centrex”-type systems, which are not truly enterprise networks, but telephone lines rented out by the telephone services provider for dedicated use,

- Key telephone systems, allowing users to accept incoming calls or make outgoing calls by pressing the dedicated key on their telephone set

- Primary rate integrated services digital networks or ISDNs.


Major PBX systems providers include:

- Mitel,

- Hitachi,

- Lucent technologies,

- Northern Telecom or Nortel,

- NEC,

- Siemens,

- GTE,

- Fujitsu


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