What Is a PBX Switchboard?

By Julie Davoren

Updated September 26, 2017

PBX switchboard systems are proprietary business telephone systems
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PBX is an acronym for "private branch exchange," an in-house telephone switching system used to interconnect both internal and external telephone extensions and networks. Its functions include least-cost routing for external calls, conference calling, call forwarding and call accounting. A PBX switchboard is a telephone system that uses switches, indicators and a controlling apparatus for electric circuits to monitor telephone lines and networks.


The Private Manual Branch Exchange (PBMX), the earliest PBX switchboard, was first used in Richmond, Virginia in 1882. The PBMX was exceptionally manual, and lawyers in the area used it for switching calls. In 1888 electromechanical and then electronic switching systems replaced the PBMX. Electronic switching systems, also known as private automatic branch exchanges (PABX), slowly started gaining popularity, and by 1910 police patrols began using these electronic systems.


All PBX switchboard systems include an internal switching network -- a microcontroller for data processing, control and logic. System cards include switching and control cards, a logic card, power cards and related devices that power switchboard operations. Telephone lines and exterior Telco trunks for signal delivery must be available for proper operations. Uninterruptible power supply (UPS) is also crucial in case of shortage or power interruption. Other smaller, but vital, components include wiring, closets, vaults, cabinets and housings.


PBX switchboards are used primarily for processing connections according to user requirements, such as to establish circuit connections between the telephones of two or more users. The PBX switchboard is also used maintain consistency of all connections as long as the users need them by channeling voice signals from one user to another. It also provides information necessary for accounting purposes, including material calls. Other call capabilities include automatic attendant and dialing, automatic call distributor and directory services, automatic call ring back, blocking, waiting, and call park and transfer.


Physical PBX hubs are typically low-profiled, only taking up a small space. Further, PBX switchboard systems reduce communication costs by incorporating emerging technologies such as VoIP to replace expensive hardware. The systems are programmable, and, therefore, can support complicated installation and integration requirements; this means that you can expand your system as your company grows. Newer PBX switchboard systems contain a number of improved features including fax-to-mail, caller ID and music on hold. Although PBX systems are typically proprietary, hosted PBX systems -- switchboards managed by external companies -- are also available.