Terminal Equipment (TE); Integrated Services Digital Network (ISDN); Multipoint Communications for Audiovisual Services; Main Functionalities and Basic Requirements for Multipoint Control Units (MCUs)
This ETS specifies the functional requirements applicable to a Multipoint Control Unit (MCU)@ or a set of interconnected MCUs@ which allows several audiovisual terminals to communicate simultaneously using single or multiple digital channels up to 1 920 kbit/s when interconnected through the pan-European Integrated Services Digital Network (ISDN). This ETS specifies the basic in-band signalling procedures to be supported to control the operation of MCU and audiovisual terminals involved in a simple multipoint communication or a basic video/ audiographic conference as specified in other standards. This ETS includes an overall description of the basic and optional functionalities of a MCU@ and lists the related requirements. Annex A (informative) describes the various requirements which apply to audiovisual terminals in order to ensure their capability to take part in multipoint communications. A MCU with any interface connected to the ISDN via a Channel Aggregation Unit (CAU) and/or special interface adapters may be used for multipoint communication when the composite equipment complies with all requirements specified in this ETS. However@ the various related pieces of equipment are outside the scope of this ETS. A MCU may establish conferences which include not only audiovisual terminals connected through an ISDN@ but also some audiovisual terminals directly linked through digital leased lines. A MCU may set up a conference where the connected terminals include not only videoconference and videotelephony terminals but also Audiographic conference@ 7 kHz telephony or 3@1 kHz telephony terminals. The description of protocols and requirements is limited to the basic multipoint communication established between various terminals supporting 3@1 kHz telephony@ 7 kHz telephony@ or the Videotelephony teleservice. The protocols and requirements necessary to support more sophisticated services@ such as Videoconference@ Audiographic conference@ or applications based on data transmission are not considered here. NOTE 1: The T.120 series of ITU-T Recommendations presently developed by ITU-T SG 8 should be used to support such enhanced functionalities. Use of the protocol specified in ITU-T Recommendation H.243 to support these functionalities should be precluded since it would result in incompatibilities between MCUs and/or terminals. NOTE 2: In the case of interworking with Public Switched Telephone Network (PSTN) or mobile telephony terminals@ echoes and/or transmission delays can degrade the audio communication quality to an unacceptable level. A MCU may be owned either by a public service provider or by a private customer. In the latter case the equipment is part of a Private Telephone Network. The D-channel signalling protocol used to set up@ modify and clear a multipoint communication is outside the scope of this ETS. On line procedure and/or protocol to be used by an end user to require@ modify or cancel a conference reservation is outside the scope of this ETS. Implementation of the T.120 series of ITU-T Recommendations for the support of the enhanced functions associated to various options of the videoconference service (e.g. Conference control@ multipoint data communication service) is outside the scope of this ETS. Conformance to this ETS will be demonstrated by checking that all mandatory functional requirements are supported during execution of a test suite which is specified in other ETSs.