ITU-T standardization activities for interactive multimedia communications on packet-based networks: H.323 and related recommendations

The Telecommunication Sector of the International Telecommunication Union (ITU-T) has developed a series of recommendations together comprising the H.323 system that provides for multimedia communications in packet-based (inter)networks. This series of recommendations describe the types and functions of H.323 terminals and other H.323 devices as well as their interactions. The H.323 series of recommendations includes audio, video and data streams, but an H.323 system minimally requires only an audio stream to be supported. Motivated by straightforward interoperability with the ISDN and PSTN networks and a variety of other protocols, the recommendation H.323 has been accepted as bang the standard for IP telephony, developed by the ITU-T and broadly backed by the industry-which is also adopted by both the Voice over IP (VolP) forum and the European Telecommunication Standards Institute (ETSI). This paper presents an overview of the H.323 system architecture with all its functional components and protocols and points out all the related specifications.