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 17 of Recommendation ITU-T H.245 shall comply with all of the mandatory requirements of this Recommendation. Version 17 products can be identified by Recommendation ITU-T H.245 TerminalCapabilitySet messages containing a protocolIdentifier value of {ITU-T (0) recommendation (0) h (8) 245 version (0) 17}. Relative to Recommendation ITU-T H.245 Version 16 (2011), this version incorporates the following changes: – Add procedures in Annex V to support better interoperability between IPv4 and IPv6 devices. – Updated Table VIII.1 to support the revisions made to Recommendation ITU-T H.241. – Support of an SCTP media transport in H.323 systems, including the addition of Annex U. – Support of DTLS media transport in H.323 systems, including the addition of Annex U. – Support of out of band data channel establishment for Annex U. – Propose updates to Recommendation ITU-T H.245 to support SCTP: split dtls-sctp into udp-dtls-sctp and tcp-dtls-sctp. – Add ExtendedAudioCapability and ExtendedDataApplicationCapability in Recommendation ITU-T H.245. Corrigendum 1 corrects errors in variable names in the description text as well as in the ASN.1 code.