This Recommendation specifies syntax and semantics of terminal information messages as well as procedures to use them for in-band negotiation at the start of or during communication. The messages cover receiving and transmitting capabilities as well as mode preference from the receiving end@ logical channel signalling@ and Control Indication. Acknowledged signalling procedures are specified to ensure reliable audiovisual and data communication. This Recommendation covers a wide range of applications@ including storage etrieval@ messaging and distribution services as well as conversational. It applies to@ but is not limited to@ multimedia systems that use the multiplexes defined in Recs ITU-T H.222.0@ ITU-T H.223@ and ITU-T H.225.0. These different systems share the same syntax and semantics@ and are therefore bit-wise compatible. Some of the procedures are applicable to all systems@ while the others are more specific to particular systems. The different systems that make use of this Recommendation may specify the use of different transport protocols. However@ it is intended to be used with a reliable transport layer@ that is@ one that provides guaranteed delivery of correct data. NOTE ?C There should be no confusion with the ITU-T T.120 management system@ which is carried within the data stream@ and covers different functionalities from those described here ?C the ITU-T H.245 stream and the ITU-T T.120-data stream are complementary.