The terms Voice over IP (VoIP) and IP Telephony (IPT) are often used interchangeably. There is an important difference however. VoIP is the art and science of placing voice in IP packets. IPT is VoIP plus signaling and features. Note this means that all IPT solutions are VoIP, but not all VoIP solutions are IPT.
The classic example of a VoIP application is replacing the tie lines between traditional PBXs with an IP backbone. The backbone network is simply being used to carry voice between the two PBXs. It is a form of trunking. Embedding voice in an application is often simply VoIP. For example, several e-learning platforms (e.g., CentraOne), make it possible for an instructor to speak in real time to the students in the virtual classroom. Students can also be given the chance to respond or ask questions, also within the application. This is a VoIP enabled application.
IPT is about doing what people do with telephones: it's about making calls. The telephones involved are IP-based phones. The signaling intelligence to determine who is calling whom is supported using IP-based protocols like the Session Initiation Protocol (SIP).
Cisco has further muddied the waters by introducing the more vacuous term IP Communications (IPC). In the Cisco world, this reflects a completely converged network that includes data, voice, and video.
realizado por Daniel Casique EES seccion 1