H.323 is a standard for audio and video conferencing established by the International Telecommunication Union (ITU).

What is H.323?

A standard for audio and video conferencing established by the International Telecommunication Union (ITU). H.323 is a comprehensive standard for multimedia communication among computers, terminals, network devices, and network services running on connectionless networks that do not support intrinsic quality of service (QoS) functions, such as Internet Protocol–based networks and the Internet.

This standard is widely accepted by manufacturers of Voice over IP (VoIP) and Internet phone software and devices. Any hardware or software system that supports the H.323 standard can communicate with any other H.323 system. H.323 is designed to make multimedia communication over the Internet as standardized as telephone communication.

For example, with telephone communication you can purchase telephone equipment from any vendor and plug it into your phone system, and the equipment works. The idea is to make Internet communication appliances just as easy to use.

How it works

H.323 defines a protocol stack that performs functions related to establishing and maintaining real-time multimedia communication that involve transmission of audio, video, and data. H.323 does not represent one standard, but rather an umbrella of other ITU standards. The H.323 protocol stack includes more than two dozen G-level, H-level, and T-level protocols from the ITU. H.323 is designed to run over Internet Protocol (IP) and includes specifications for the following components:

  • H.323 Conference Manager, which manages the establishment of multimedia conferencing connections
  • The H.245 protocol, which controls communication with data terminal equipment (DTE)
  • The H.225 protocol, which performs synchronization and framing mechanisms for multimedia data streams
  • The T.120 protocol, which provides support for real-time, multipoint data communication

H.323 also specifies standard codecs for audio (G.723) and for video (H.263) that enable H.323 products to send and receive voice and video images. Specifically, H.323 defines standards for data codecs for audio transmission rates of 14.4 Kbps or faster and video transmission rates of 28.8 Kbps or faster. H.323 recognizes the T.120 protocol for data conferencing and provides a set of standards-based conferencing features for audio and video conferencing.