I did a presentation for MERCI people in march 1996 when IMTC members and other companies signed up for supporting the ITU H.323 and T.120 standards under the parole "Standards first". My presentation was a pedagogical disaster, mainly because I was too busy to prepare a demonstration setup of the MBone tools and reading up on ITU H.323, but here's a brief summary I gave for the Tecodis in spring 1997.
H.32x is a family of "umbrella-standards" for video telephony over
different network types. In the standards are specified how bridges between
the different H.32x-standards should work as well as minimal compliance
requirements.
Here's a little table over what the different H.32x
Video
Teleconferencing Standards may include.
The H.32x standards is promoted by International Multimedia Teleconferencing Consortium ( IMTC). IMTC is based in San Ramon, California and consists of more than 125 member-companies and -organisations from 20 countries. The consortium holds interoperability testing between different vendors and tries to resolve ambiguities in the H.32x recommendations.
Voice Over IP (VoIP) is an activity group within IMTC concerned with Internet telephony.
H.323 is an umbrella standard for video telephony over unreliable packet
networks (IP, Ethernet, Token Ring, et.c). It's minimal scope consists
of an audio standard plus multiplex (H.225.0?) and H.245 signalling.
H.323 use RTP for transport over IP networks.
VoIP and IMTC recommends it's users to use G.723.1 as default audio codec
and ITU-T will incorporate this recommendation into H.323.
G.723.1 is owned by AudioCodes, DSP Group, France Telecom, University of
Sherbrooke, ATT, Lucent, VoiceCraft, and NTT and have to be licenced.
T.120 is an umbrella-standard for "Transmission Protocols for Multimedia Data" over ISDN (H.320) and PSTN (H.324). It's currently revisioned to support the remaining H.32x as well. T.120 includes
Maintained by Tobias Öbrink