H.323 (Teleconferencing Protocol)

ITU-T H.323 teleconferencing protocol is the international standard for multimedia communication over packet-switched networks, including LANs, WANs, and the Internet - transporting voice and video Voice over IP (VoIP) and video networks around the world. It was first defined by the ITU in 1996 and has been updated regularly. The most recent version is H.323 version 5 (2003).

The scope of H.323 covers real-time voice, video, and data communication over packet-switched networks. It was designd from the outset to operate over IP networks, primarily, though H.323 may also operate over other packet-switched networks. It was designed with multipoint voice and video conferencing capabilities, though most users do not take advantage of the multipoint capabilities specified in the protocol.

H.323 is an "umbrella" specification, which includes the standards H.323, H.225.0, H.245, the H.450-series documents, and the H.460-series. It allows for the use of T.120 for data collaboration and file transfer. When referring to the system and set of documents, people generally refer to "H.323", though not every document is mandatory as part of a standard H.323 system.

Note: H.323 and SIP are two VoIP standards.  Although the two standards are approaching each other, their focus and applicability is still different. It is not expected that one of the two protocols will dominate over the other. They will probably coexist in different environments and implementations over a longer time, which will also place a strong requirement on interworking between them.