How a PBX telephone system works

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How a PBX telephone system works

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What Is PBX?

PBX is an abbreviation for Private Branch Exchange. A PBX system is a private telephone switch that is installed in a business location to facilitate communication between people inside the organisation while allowing access to adequate external telephone lines.

Incoming Traditional PBX Calls

Traditional PBX systems allow for the transfers of calls from a public switched telephone network to a private switched network. Calls on incoming lines are routed through a private switching system to a telephone with a private number in the private system.

Outgoing Traditional PBX Calls

Internal telephones on a PBX network enters a code, usually 0 or 1, to access an outside line. Once the private line is connected to an outside line, the caller dials the call normally.

Internal PBX Calls

Calls between private telephones on a traditional PBX system work similarly to calls between private lines on a traditional public switched network. The difference is that the calls on the PBX are run over private, internal telephone lines and switches.

Traditional PBX Technology

Traditional PBXs are automated replacements for old-time operators with plug boards. A PBX is an automated system that switches calls between circuits. Instead of manually connecting a call with a patch cable, a PBX uses a miniature switch to route the analogue signal. Traditional PBX systems started out with analogue technology and were more limited in the number of telephone lines they could support. Eventually, analogue PBX switches were replaced with digital switches to support higher densities of both internal telephone lines and connections to external lines and trunks.


The advent and popularity of voice over Internet protocol (VOiP) networks have resulted in completely digital PBX systems that use digital technology and Internet protocol (IP) to route phone conversations to the proper telephone handset. IP-PBX systems are less expensive than traditional PBX systems and are much easier to configure. An additional advantage of an IP-based PBX is that the system can support traditional telephone handsets or software-based telephones. With a software-based telephone, a user plugs a headset into a computer and uses a virtual telephone to dial and receive telephone calls. Another advantage of an IP-based PBX is the ability to transmit calls internationally over the Internet, thereby avoiding long-distance charges. The advent of IP-PBX technology has allowed companies to have entire call centres in areas with lower labour costs.

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