H.323 - Packet-based multimedia communications systems
H.225 - call control protocol
H.235 - security
H.245 - media control protocol
Q.931 - digital subscriber signalling
H.450.1 - Generic functional protocol for the support of
supplementary services in H.323
Annex D - Real Time fax over H.323
Annex E - Multiplexed call signalling
Annex F - Simple Endpoint Terminal (SET)
Annex G - Text SET
Annex H - Mobility
Annex I - Operation over low QoS Networks
Annex J - Secure SET
Annex K - HTTP Service Control Transport
Annex L - Stimulus Signalling
Annex M - QSig Tunneling
Annex N - QoS
G.711 - PCM audio codec 56/64 kbps
G.722 - audio codec for 7 Khz at 48/56/64 kbps
G.723.1 - speech codec for 5.3 and 6.3 kbps
G.728 - speech codec for 16 kbps
G.729 - speech codec for 8/13 kbps
H.261 - video codec for >= 64kbps
H.263 - video codec for < 64kbps
H.320 - The original ISDN videoconferencing standard.
H.324 - An extension of H.320 for videoconferencing over PSTN lines
T.120 - Real time data conferencing protocol
Where do standards document come from?
The documents covering the H.323 protocol suite are created by the
International Telecommunications Union (ITU).
The International Multimedia Teleconferencing Consortium (IMTC) is a
consortium of companies that promote the use of multimedia communications,
hold interoperability events, etc. The membership of the IMTC covers most of the big
telcos and companies, and membership is "open" to anyone who can afford the
US$US6000 per year membership fee.
All of the ITU standards relating to H.323 can be found here.
It can be hard to find the document you need on this site.
Fortunately, Paul E Jones of Cisco has an excellent web site on which references all of
the latest H.323 specifications by name, and contains links (where available) to the
appropriate draft specification for download. His site is at: