VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.
VoIP specifically refers to sending voice traffic over an IP (Internet Protocol) network. Voice and data convergence refers to sending both voice and data (such as LAN traffic) over any data network (typically an IP network, frame relay network or ATM network).
IP telephony refers to any "telephone" type service carried over IP - this could include faxing. VoIP is voice over IP only. Sometimes telephony also includes text messaging.
This was first published in November 2003