H.323

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 Voice-over-IP (VoIP) (a.k.a., 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.