A PBX (Private Branch Exchange)
is a private telephone network used within an enterprise. It makes connections
among the internal telephones of the enterprise and also connect them to the PSTN
(Public Switched Telephone Network)
through a number of outside lines, which allows the users of the PBX to make
external phone calls.
In these days the most popular trend in PBX development is the VoIP PBX, that
transmits calls by using the IP protocol (Internet Protocol).
It is also known as IP PBX, which is a software based PBX, that provides audio,
video, and instant communication through the TCP/IP protocol (Transmission Control Protocol)
for the internal network, and it connects this internal network with the PSTN.