- Private Branch Exchange
- A Private Branch Exchange (PBX) is a call switching device owned and operated by a private organization in order to allow them to better control calls after they reach the company. It operates very similarly to a telephone company's switching device, except it does not perform certain functions that by law can only be performed by the phone company.
A Private Branch Exchange is used to connect a business, school, hospital, government office or other organization to one or more of the phone company's central offices. Through the PBX device, workers or members can place calls internally within the organization or to external numbers. Modern PBX's can also provide additional services such as voicemail, conferencing, call waiting, call forwarding, interactive voice response, call attendants and call recording.
When an organization purchases a PBX, they also contact the phone company and purchase one or more trunk lines to tie the PBX to the local central office. The PBX can then exchange calls with the external phone service while still handling internal calls within the organization.
Telephone companies assign a range of telephone numbers for use on the PBX and the organizations PBX administrator assigns individual telephone numbers to specific phones in the organization. Some or all of those telephone numbers may be dialed from outside the company. If the number can be reached from the external public phone system, it is called a Direct Inward Dial number (or a Direct Dial-In number in Europe).