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Collaboration, Voice & AV · Advanced

H.245

The H.323 control protocol that exchanges capabilities, determines master/slave and opens logical channels for media.

Definition

H.245 runs after H.225 call setup, either on a separate TCP connection or tunneled inside H.225 messages. It performs terminal capability set exchange (codecs), master/slave determination and open logical channel procedures that tell each side where to send RTP. H.323 Fast Connect (Fast Start) shortcuts this by embedding channel proposals in the SETUP message.

Example

A mismatched capability set causes H.245 to fail and the call drops shortly after connecting.

Exam tip

H.245 equals capability and media channel negotiation; H.225 equals call setup.

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