H.245 is a protocol for the transmission of call management and control signals in packet-based networks using H.323 equipment. The H.245 specification is used in audio, video, and data transmissions, as well as in voice over IP (VoIP). H.245 messages are sent over special channels called H.245 control channels.
H.245 signaling is used to manage and control various aspects of call setup and connection. Functions of H.245 include determining which endpoint is to be the master and which is to be the slave during the call, opening and closing of multiplexed data-transfer paths between the endpoints, establishing an upper limit to the data transfer speed on each logical channel, information exchanges between endpoints concerning the types of data each endpoint can send and receive, requests by the receiving endpoint for changes in the mode of the data sent by the transmitting endpoint, and requests by either endpoint to end the call.
H.323 is a standard approved by the International Telecommunication Union (ITU) to promote compatibility in videoconference transmissions over Internet Protocol (IP) networks. H.323 defines how communications occur between terminals, network equipment, and services.