maintenance. H.231 The formal name for this specification is "Multipoint Control Unit for Audiovisual Systems using Digital Channels up to two Mbps." H.231 defines the network configuration for an H.320-compliant multipoint control unit (MCU). The MCU is used to bridge three or more H.320-compliant codecs together in a simultaneous conference. The procedures and functionality of a H.231 MCU are defined in a companion standard, H.243. Video Communications: The Whole Picture H.242 The formal name for this specification is "System for Establishing Communication Between Audiovisual Terminals Using Digital Channels up to two Mbps." Recommendation H.242 defines the protocol for establishing an audiovisual session, and subsequently disconnecting that session. During an H.242 call set-up, a terminal indicates its capabilities to other terminals. H.242 defines signaling procedures for identifying a compatible mode, for initiating a conference using that mode and for switching between modes throughout a call. Besides that very important exchange, H.242 covers basic sequences for in-band information exchange. It details procedures for recovering from faults; it specifies procedures for adding channels to, removing channels from, and transferring calls into the session. This Recommendation also works with H.221 to permit a digital channel to accommodate audio, video, and data across a range of data rates. Signaling procedures allow codecs to identify how different portions of the channel are allocated. H.243 The formal name for this specification is "System for Establishing Communication Between Three or More Audiovisual Terminals Using Digital Channels up to two Mbps." Recommendation H.243 is a companion standard to H.231. It describes procedures and functionality for multipoint video communication. Included in the features are chair control/directorship, determining which site will broadcast at any given time, muting video and audio from specific terminals as desired, etc. THE H.32X FAMILY The ITU-T has developed, and is c