Yong Qiu Liu's Web Page--T

Yong Qiu Liu's Web Page--T_120

Networking service systems and related standards

3.4 T.120 Data

The T.120 is a recommendation of ITU, which contains a series of communication and application protocols and services supporting real-time, multipoint data communications. ^[25]

T.120 specifies the document conferencing and application sharing (or data conferencing) section of a multimedia teleconference. It describes a method to distribute files and graphical information in real-time efficiently and reliably during a multipoint multimedia meeting. These standards are proposed to assure interoperability between each end user, to specify infrastructure protocols for audiographic or audiovisual applications and to permit data sharing among participants in a multimedia teleconference, which includes white board image sharing, graphic display information, image exchange and application sharing.It covers the audiographic portion of the H.320, H.323, and H.324 series and operates either within these or by itself.^[26]

Architecture: There are three main layers that are needed to deliver the best quality that can be provided by T.120.^[31]

Plumbing Layer (minimal requirement for T.120)

Protocol Layer (conditional protocols)

Application Layer (not specified under T.120 recommendations)

T.120 is based on a multilayered structure where the defined protocols and service definitions are supplied between layers. As shown in Figure A-2, T.122, T.123, T.124, and T.125 are located on the lower level layers which specify a mechanism to enable multipoint data communication between applications. T.126 and T.127 are located on the upper level layers to support conferencing applications, such as shared whiteboarding and multipoint file transfer. Using these protocols applications can share the same conference with other applications that use other protocols. ^[25]

Figure A-2 The T.120 architecture.^[25]

Most of the recommendations in T.120 are summarized in Table A-1.^[26]

Table A-1 ITU T.120 Standard^[26]

Name	Description
T.120	Data protocols for multimedia conferencing: This provides an overview of the T.120 series.
T.121	Generic Application Template: This provides a guide for the development of T.120 application protocols.
T.122	Multipoint Communication Service (MCS) Service Description: This describes the multi-point services available to developers
T.123	Protocol stacks for audiographic and audiovisual teleconference applications: This specifies transport protocols for a range of networks.
T.124	Generic Conference Control (GCC): This defines the application protocol supporting reservations and basic conference control services for multipoint teleconferences.
T.125	Multipoint Communication Service (MCS) Protocol specification: This specifies the data transmission protocol for multipoint services.
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.
T.127	Multipoint Binary File Transfer Protocol: This defines a method for applications to transmit files in a multipoint conference.
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.
T.134	Text chat application entity: A T.121 APE definition for a text chat protocol.
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").
T.136	How Remote Device Control and configuration may be performed using T.120 as the transport protocol.
T.140	Protocol for multimedia application text conversation. The protocol for text chat within T.120, goes with T.134.

Last update April 1, 2002