T.120 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.
T.120 Overview
The T.120 standards cover the document conferencing and application
sharing (sometimes called data conferencing)
portion of a multimedia teleconference. The recommendations specify how to
efficiently and reliably distribute files
and graphical information in real-time during a multipoint multimedia
meeting. The objective of the standards is to
assure interoperability between terminals without either participant
assuming prior knowledge of the other system;
permit data sharing among participants in a multimedia teleconference,
including white board image sharing, graphic
display information, and image exchange, application sharing, and, specify
infrastructure protocols for audiographic or
audiovisual applications.
The T.120 series governs the audiographic portion of the H.320, H.323, and
H.324 series and operates either within
these or by itself. The T.120 suite consists of a series of
recommendations, which are summarized, along with their
current ITU status in Table 1.
Table 1: ITU T.120 Standard
Recommendation
Description
ITU Status (as of Oct.
'98)
T.120
Data protocols for multimedia
conferencing: This provides an
overview of the T.120 series.
Ratified
T.121
Generic Application Template: This
provides a guide for development of
T.120 application protocols.
Ratified
T.122
Multipoint Communication Service
(MCS) Service Description: This
describes the multi-point services
available to developers
Ratified
T.123
Protocol stacks for audiographic and
audiovisual teleconference
applications: This specifies transport
protocols for a range of networks.
Ratified
T.124
Generic Conference Control (GCC):
This defines the application protocol
supporting reservations and basic
conference control services for
multipoint teleconferences.
Ratified
T.125
Multipoint Communication Service
(MCS) Protocol specification: This
specifies the data transmission
protocol for multipoint services.
Ratified
T.126
Multipoint still image and annotation
protocol: This defines collaborative
data sharing, including white board
and image sharing, graphic display
information, and image exchange in a
multipoint conference.
Ratified
T.127
Multipoint Binary File Transfer
Protocol: This defines a method for
applications to transmit files in a
multipoint conference.
Ratified
T.128
Multipoint application sharing
protocol: This defines how
participants in a T.120 conference can
share local applications such that
other conference participants can see
the image of the shared application,
and use the mouse and keyboard to
take control of the shared application
as if it were running locally.
Ratified
T.134
Text chat application entity: A T.121
APE definition for a text chat protocol.
Ratified
T.135
User-to-reservation system
transactions within a T.120
conference: This defines conferencing
reservation protocols in a T.120
environment, typically between a
client application and a scheduling
systems which reserves resources for
multipoint control units (MCUs or
"bridges").
Ratified
T.136
How Remote Device Control and
configuration may be performed using
T.120 as the transport protocol.
Draft, for decision 4/99
T.140
Protocol for multimedia application text
conversation. The protocol for text
chat within T.120, goes with T.134.
Ratified
T.VMR
Virtual Meeting Room control.
Contains some material from previous
T.13x drafts, concentrates on audio +
dataconferencing.
Draft
As noted in Table 1, the core T.120 standards are ratified. This includes
the Application or Upper Level Layers (T.126,
T.127) and the Infrastructure or Lower Level Layers (T.122/125, T.123,
T.124, T.128, T.134, T.135, T.140).
Work on other recommendations continues in the ITU. Within the IMTC, the
Multipoint/Multiparty activity group,
Data Conferencing, and API and Protocols activity groups are coordinating
submissions. Additionally, the T.120
Interoperability activity group is coordinating and implementing test
sessions to verify the interworking of products
and services based on these standards.
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