H.323 is the result of an International Telecommunications Union (ITU) specification for computers, equipment and services concerned with multimedia communications over networks that fail to offer a guaranteed quality of service. H.323 allows for the transmission of real time video, audio and data and has been specifically designed to provide the protocols that need to be observed in order to make available audio-visual communications on any packet network. In addition the H.32x series of Protocols encapsulate H.323 in order to provide services over ISDN, PSTN or SS7. H.323 provides a similar function to that of the Session Initiation Protocol when used in Voice Over Internet Protocol (V0IP), Internet telephony or IP Telephony. Early availability of H.323 provided a ready made set of standards that not only detailed the basic call model it also addressed issues relating to business communications expectations.
The flexibility of the H.323 infrastructure was recognized by Microsoft during the development of its NetMeeting audio and video conferencing with the result that NetMeeting features are based around H.323. This significant undertaking allowed NetMeeting to exchange communications with other H.323 standards-based products while the use of H.323 as the foundation on which to place the building blocks for NetMeeting proved correct as highlighted by the fact that NetMeeting is able to initiate and maintain audio and video connections while also reducing compatibility issues that might otherwise have limited performance. In relation to Conferencing Products and Services NetMeeting should be able to operate with any H.323 conferencing product or service found on TCP/IP connections.
H.323 compatibility extends to include other ITU-T protocols such as those summarized below:
• H.225.O details call signaling, audio and video media, stream packet construction, media stream synchronization and control message formats.
• H.245 details controls the protocols that govern the descriptions of messages and procedures used to open and close logical channels for audio, video and data.
• H.450 details an explanation of Supplementary Services.
• H.235 details security contained in H.323.
• H.239 details the use of dual stream in videoconferencing.
• H.460.17-19 details firewall navigation within the H.323 environment.
The breadth of H.323 usability extends to include components such as the Multipoint Control Unit (MCU) which in relation to H.323 makes possible a connection between three or more H.323 terminals and participation in a multipoint conference. In addition H.323 gateways which are the translation apparatus related to call signaling, data transmission, and audio and video transcoding fulfills the role that addresses interoperability issues. Also Gatekeepers interact with H.323 devices by controlling the number and type of connections entering a network; directing a call to the correct destination whilst managing the network address for incoming calls.
With compatibility issues significantly reduced through the adoption of H.323 products and the fact that H.323 has not yet reached its full potential with improved security and interoperability in relation to streaming media servers appearing a strong possibility for the future. H.323 continues to offer a useful communications apparatus and one that should endure for some years yet.