PBX, also known as SPC exchange, completes telephone exchange between enterprises and public telecommunication network, and combines telephone, fax, modem and other functions. General term ext (extension) refers to the extension connected to the main line. The PBX is to handle the calls between extensions and then connect with the Public Switched Telephone Network (PSTN) through the trunk line.

PBX is commonly known as SPC exchange, SPC PBX, telephone exchange, group telephone, etc. PBX is one of the commonly used means of telephone communication management in modern office, which enables telephone managers to manage external calls and internal calls collectively.