Call Center Technology: PBX - Private Automatic Branch eXchange

A Private Branch eXchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public. PBXs are also referred to as:

PABX - Private Automatic Branch eXchange
EPABX - Electronic Private Automatic Branch eXchange

Short for private branch exchange, a private telephone network used within an enterprise. Users of the PBX share a certain number of outside lines for making telephone calls external to the PBX.

Most medium-sized and larger companies use a PBX because it's much less expensive than connecting an external telephone line to every telephone in the organization. In addition, it's easier to call someone within a PBX because the number you need to dial is typically just 3 or 4 digits.

A new variation on the PBX theme is the Centrex, which is a PBX with all switching occurring at a local telephone office instead of at the company's premises.

PBX System Components

The PBX’s internal switching network.

Central processor unit (CPU) or computer inside the system, including memory.

Logic cards, switching and control cards, power cards and related devices that facilitate PBX operation.

Stations or telephone sets, sometimes called lines.

Outside Telco trunks that deliver signals to (and carry them from) the PBX.

Console or switchboard allows the operator to control incoming calls.

Uninterruptible Power Supply (UPS) consisting of sensors, power switches and batteries.
Interconnecting wiring.

Cabinets, closets, vaults and other housings.

PBX Functions

Functionally, the PBX performs three main duties:

Establishing connections (circuits) between the telephone sets of two users. (e.g. mapping a dialed number to a physical phone, ensuring the phone isn't already busy)

Maintaining such connections as long as the users require them (i.e. channeling voice signals between the users)

disconnecting those connections as per the users requirement

Providing information for accounting purposes (e.g. metering calls)

How PBX Works?



A PBX (Private Branch Exchange) is a switch station for telephone systems। It consists mainly ofseveral branches of telephone systems and it switches connections to and from them, thereby linking phone lines.

Companies use a PBX for connecting all their internal phones to an external line. This way, they can lease only one line and have many people using it, with each one having a phone at the desk with different number. The number is not in the same format as a phone number though, as it depends on the internal numbering. Inside a PBX, you only need to dial three-digit or four-digit numbers to make a call to another phone in the network. We often refer to this number as an extension.