An IP PBX is a PBX that supports the IP protocol to connect telephones by using an Ethernet or packet-switched LAN. It sends voice conversations in IP or data packets. An IP PBX may have multiple interfaces. These include interfaces for a data network and other interfaces that allow for a connection to a telephony or circuit-switched network.
The development of real-time Internet protocols has made it possible to successfully send voice and fax messages over a data network. Such real-time Internet protocols include the VoIP protocols used with Unified Messaging: Session Initiation Protocol (SIP) over Transmission Control Protocol (TCP) for voice messaging.
These protocols have made it possible to successfully send voice and fax messages over a data network. Real-time VoIP protocols are required to send voice messages over a packet-switched or data network so the delivery order and timing of data packets can be maintained and controlled. If these protocols weren't used to maintain and control the delivery and timing of the data packets, a person's voice would be broken up and sound incoherent or the images might appear garbled.