ITU-T Recommendations

Recommendation ITU-T H.245 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.

Products claiming compliance with Version 16 of ITU-T H.245 shall comply with all of the mandatory requirements of this Recommendation. Version 16 products can be identified by ITU-T H.245 TerminalCapabilitySet messages containing a protocolIdentifier value of {ITU-T (0) recommendation (0) h (8) 245 version (0) 16}.

Relative to ITU-T H.245 Version 15 (2009-12), this version improves harmonization with SIP by making the following changes:

– allowing a new dynamic payload number to be specified in the ITU-T H.245 OpenLogicalChannelAck message;
– revising clause B.3.2 to indicate that ITU-T H.323 systems should use the dynamic payload type specified in the ITU-T H.245 OpenLogicalChannelAck message instead of the dynamic payload type specified in the ITU-T H.245 o pen logical channel message;
– defining a similar mechanism for logical channels that use multiple payload types; and
– defining a new capability in a new annex, Annex T, that specifies that an endpoint is capable of using the dynamic payload type replacement mechanisms in the ITU-T H.245 OpenLogicalChannelAck message.