H.323 Overview
Multimedia Teleconferencing Standards
The ITU-T T.120, H.320, H.323, and H.324 standards comprise the core
technologies for multimedia teleconferencing.
The T.120 standards address Real Time Data Conferencing (Audiographics),
the H.320 standards address ISDN
Videoconferencing, the H.323 standard addresses Video (Audiovisual)
communication on Local Area Networks, and
the H.324 standard addresses video and audio communications over low
bitrate connections such as POTS modem
connections.
Each of these standards has been developed in accordance with the process
described above. The IMTC expects to
continue to contribute, through its members, to the future enhancement of
the standards to incorporate new
functionality and capabilities.
H.323 Overview
The H.323 standard was originally developed as an adaptation of H.320,
which addresses videoconferencing over
ISDN and other circuit switched networks and services. Since H.320 was
ratified, in 1990, corporations have
increasingly implemented Local Area Networks (LANs) and LAN gateways to
the Wide Area Network (WAN). H.323
has evolved beyond a logical and necessary extension of the H.320 standard
to include Corporate Intranets and
packet-switched networks generally. H.323 utilizes the Real-Time Protocol
(RTP/RTCP) from the IETF, along with
internationally standardized codecs. With the ratification of version 2,
H.323 is also being used for video and other
communications, over the Internet.
In common with the other ITU multimedia teleconferencing standard, H.323
applies to multipoint and point-to-point
sessions. The components of the standard are summarized in Table 1.
Table 1: Components of H.323
With the ratification of these core components, and the range of networks
H.323 can be applied to, products and
services based on H.323 are beginning to appear. As a result,
interoperability is beginning to assume critical
importance.
The IMTC is addressing this concern through its activity groups.
Specifically, IMTC's Corporate Network
Conferencing activity group conducted the first industry-wide H.323
interoperability test session in October 1996.
Additional sessions were held in December 1996 and February 1997, with
more sessions scheduled throughout 1997.
This group is also coordinating with IMTC's POTS and H.320
Interoperability activity groups, to extend this testing to
H.324 and H.320 products.
Recommendation
Description
Status (as of Oct. `98)
H.323
Systems document, describes overall
operation and procedures for H.323
systems.
Version 2 Ratified
H.225.0
Specifies messages for call control
including signaling, registration and
admissions, and packetization/
synchronization of media streams
Version 2 Ratified
H.245
Specifies messages for opening and
closing channels for media streams,
and other commands, requests and
indications.
Version 3 Ratified
H.450.x
Series of Suplimentary service
recommendations. Defines signalling
and procedures used to provide these
telephony-like services
Version 1 Ratified
H.235
Defines the security framework used
to provide authentication, encryption
and integrity to H.323 systems
Version 1 Ratified
H.332
Provides large scale, or
loosely-coupled conferencing based
upon H.323.
Version 1 Ratified
H.261
Video codec for audiovisual services
at P x 64 Kbps.
Ratified
H.263
Specifies a new video codec for video
over POTS.
Ratified
G.711
Audio codec, 3.1 KHz at 48, 56, and 64
Kbps (normal telephony).
Ratified
G.722
Audio Codec, 7 KHz at 48, 56, and 64
Kbps.
Ratified
G.728
Audio Codec, 3.1 KHz at 16 Kbps.
Ratified
G.723
Audio Codec, for 5.3 and 6.3 Kbps
modes
Ratified
G.729
Audio Codec, 8 kbps audio codec.
Ratified
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