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ITU-T H.231 1997 Edition, July 1, 1997
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Multipoint control units for audiovisual systems using digital channels up to 1920 kbit/s
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This Recommendation specifies the means by which three or more audiovisual terminals conforming to Recommendations H.320, H.221, H.242, H.261, H.262 and H.263 may communicate simultaneously over constant bit rate digital paths, such communication being designated a "multipoint call". The terminals should not need any modification for multipoint working, though some optional enhancements may require additional software; in particular, considerably enhanced functionality is attained via the use of T.120 protocols in the MLP channel. The interconnection is effected by one or more Multipoint Control Units (MCU) which may reside in the network or at one of the terminals.

This Recommendation covers both mandatory requirements and optional enhancements for multipoint working. The optional enhancements include:

• numbering of terminals;

• chair control;

• data broadcast;

• video mixing;

• cascading.