What Is IP Telephony?

IP Telephony is using standard computer networks and protocols to transmit telephone messages digitally.  The telephone conversation is converted to digital signals, and sent over the network using the communication standard called Internet Protocol (IP), which is the protocol used by almost all networks today.  See the illustration to the right of an IP telephony network.  (Click on the diagram for a larger version.)  This is also known as VOIP (Voice Over IP.)

What Is an IP PBX?

A Private Branch Exchange (PBX) is a telephone exchange that serves a particular business or office.  An IP PBX is an appliance that implements a PBX that uses IP telephony.  It can either be a hosted device that is located away from the user's premises, or it can be a local device.  It consists of a server computer, running specialized software for the answering, transferring, and disconnecting of telephone lines.  IP PBX's can do anything that a conventional PBX can do, and more!

What Kind of Telephone Services Can Be Used With an IP PBX?

Virtually any telephone service can be used with an IP PBX. The most common telephone service is what is officially known as Public Switched Telephone Network (PSTN.)  It also goes by POTS (Plain Old Telephone Service. )  This is the analog service that we have used for many years.  By means of a device known as an Analog Telephone Adapter (ATA), we can digitize the analog signal from a POTS line, and use it in the IP PBX.

Though not near as popular as the POTS, there are still a large number of T1 lines in use.  T1 lines are digital phone lines, with 24 channels (though partial T1's have fewer channels.)  This affords twenty-four simultaneous phone calls at one time.  Increasingly, phone companies are offering voice/data T1's, where unused channels are then utilized for Internet access, or even all data T1's, where the voice calls are routed over the digital lines using proprietary hardware.  Unfortunately, the digital signals from the T1 lines are not compatible with the IP PBX, but there are Digital Telephone Adapters available to convert the signals.

One of the newer services available are the Session Initiated Protocol (SIP) trunks.  SIP trunks can be thought of as virtual phone lines that run over the Internet.  SIP trunks are leased from SIP trunk providers, usually at a cost that is much lower than a PSTN line from a conventional telephone company.  Each SIP trunk can carry one telephone call.  In our opinion, SIP trunks are the way to go.  See our business case for IP PBX's.

There is even software that can connect Skype or Vonage to your IP PBX, but the benefits are few, and the cost higher than most SIP trunks.

Learn more about IP PBX Hardware.