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T.120: Multipoint Data Conferencing and Real Time Communication Protocols(T.121, T.122, T.123, T.124, T.125, T.126, T.127)
The ITU T.120 standard is made up of a suite of communication and application protocols, which are designedfor multipoint Data Conferencing and real time communication including multilayer protocols which considerably enhance multimedia, MCU and codec control capabilities. Depending on the type of T.120 implementations, the result product can make connections, transmit and receive data, and collaborate using compatible data conferencing features, such as program sharing, whiteboard conferencing, and file transfer. The key functionalities of T.120 are:
- Establish and maintain conferences without any platform dependence.
- Manage multiple participants and programs.
- Send and receive data accurately and securely over a variety of supported networking connections.
The T.120 protocol suite including the following protocols:
T.121: T.121 provides a template for T.120 resource management that developers should use as a guide for building application protocols. T.121 is mandatory for standardized application protocols and is highly recommended for non-standard application protocols. The template ensures consistency and reduces the potential for unforeseen interaction between different protocol implementations.
T.122:T.122 defines the multi-point services available to the developer. Together with T.125, they form MCS, the multi-point "engine" of the T.120 conference. MCS relies on T.123 to actually deliver the data. MCS is a powerful tool that can be used to solve virtually any multi-point application design requirement. MCS is an elegant abstraction of a rather complex organism. Learning to use MCS effectively is the key to successfully developing real-time applications.
T.123: T.123 specifies transport profiles for each of the following: 1) Public Switched Telephone Networks (PSTN) 2) Integrated Switched Digital Networks (ISDN); 3) Circuit Switched Digital Networks (CSDN); 4)Packet Switched Digital Networks (PSDN); 5) Novell Netware IPX (via reference profile); and 6) TCP/IP (via reference profile). T.120 applications expect the underlying transport to provide reliable delivery of its Protocol Data Units (PDUs) and to segment and sequence that data.
T.124:The T.124 specifies the Generic Conference Control (GCC), which provides a comprehensive set of facilities for establishing and managing the multi-point conference. It is with GCC that we first see features that are specific to the electronic meeting.
T.125: T.125 describes the Multipoint Communication Service Protocol (MCS). It defines: 1) Procedures for a single protocol for the transfer of data and control information from one MCS provider to a peer MCS provider. 2) The structure and encoding of the MCS protocol data units used for the transfer of data and control information.
T.126: T.126 defines a protocol for viewing and annotating still images transmitted between two or more applications. This capability is often referred to as document conferencing or shared whiteboarding.
T.127: T.127 specifies a means for applications to transmit files between multiple endpoints in a conference. Files can be transferred to all participants in the conference or to a specified subset of the conference. Multiple file transfer operations may occur simultaneously in any given conference and developers can specify priority levels for the file delivery. Finally, T.127 provides options for compressing files before delivering the data.
Protocol Structure - T.120: Multipoint Data Conferencing and Real Time Communication Protocols(T.121, T.122, T.123, T.124, T.125, T.126, T.127)
The T.120 architecture relies on a multi-layered approach with defined protocols and service definitions between layers. Each layer presumes the existence of all layers below. The lower level layers (T.122, T.123, T.124, and T.125) specify an application-independent mechanism for providing multi-point data communications services to any application that can use these facilities. The upper level layers (T.126 and T.127) define protocols for specific conferencing applications, such as shared whiteboarding and binary file transfer. These "standardized applications" can co-exist in the same conference with "non-standardized" applications such as a business card exchange program or a textual chat application. The following figure represent the architecture of the T.120.
RTSP , SIP , RTP , RTCP , SDP , Megaco/H.248, Q.931 , H.323 , H.225
T.120, T.121, T.122, T.123, T.124, T.125, T.126, T.127 are ITU-T (http://www.itu.int/ITU-T/ ) standards.
http://www.packetizer.com/conf/t120/primer/ : A Primer on the T.120 Series Standard