(VoIP) Any technology providing voice telephony services over IP, including CODECs, streaming protocols and session control. The major advantage of VoIP is lower cost, by avoiding dedicated voice circuits.
Currently VoIP is being deployed on internal corporate networks, and, via the Internet, for low cost (and low quality) international calls. It is also used for telephony applications such as voice and fax mail.
The ITU standard is H.323, which is a whole suite of protocols, while the IETF has developed the much simpler SIP to solve the session control problem and MGCP/Megaco to solve the gateway problem.