Also known as a PBX, Unified Communications System or business phone system, a PBX acts as the central switching system for phone calls within a business. IP PBX systems handle internal traffic between stations and act as the gatekeeper to the outside world. The initials PBX stand for Private Branch Exchange, a very old fashioned term for a system that has evolved significantly over the past century.
A traditional PBX is made up of two key elements: lines and stations. The lines, sometimes called trunks, are connections to the global public switched telephony network (PSTN) by way of a telephone company. Stations are simply telephones or other endpoint devices like fax machines, modems and credit card terminals.
The original mission of the PBX was to provide shared access to limited resources. Rather than having a separate phone line for each phone, a business could share a small pool of lines across a much larger pool of stations. When a call came it was answered by an operator who then connected it with the appropriate person or department. When someone inside needed to make a call, the operator connected them with an available line. Frequently these early systems were simply called “switchboards”.
Over time, operators were replaced by electromechanical and later electronic systems for managing access to lines. Additional features were added to automatically route incoming calls, to allow active calls to be transferred between stations and to permit or deny calls based on various rules. Adjunct systems were added for voice messaging, call queuing and other value added services.
Today, a business phone system is much more than just a simple switch. Adjunct technologies like automated attendant, voice messaging, call queuing and multi-party conferencing have become standard features. Basic analog and proprietary digital phones are giving way to standards-based IP phones. Outside connectivity is now available over the Internet in the form of SIP trunks or other VoIP services.
When PBXs were originally developed, wireline phone calls were the only type of electronic communication available. Today, the communications landscape has expanded to include email, instant messaging, video conferencing, desktop sharing, SMS and mobile telephony. Unified Communications is a catch-all term that describes the process of merging all of these technologies and integrating them with business processes. Unified Communications aims to increase efficiency while simplifying management.