H.323 is an umbrella recommendation from the
ITU-T, that defines the protocols to provide audiovisual communication sessions on any packet networks. It is currently implemented by various Internet real time applications as NetMeeting, Voxilla (for Linux). It is a part of the H.32X series of protocols which also address communications over
ISDN and
PSTN. A challenger to H.323 is
SIP a standard from
IETF. Both protocols are used in InternetTelephony or
IPTelephony[?]
H.323 references many other ITU-T protocols like;
- H.323 to describe the system, the call model and call signaling procedures.
- H.225[?] protocol is used to describe the media (audio and video), the stream packetization, media stream synchronization and control message formats.
- the H.245[?] describes the messages and procedures used for opening and closing logical channels for audio, video and data, capability exchange, control and indications.