What Does H.323 Mean?

H.323 is an ITU Telecommunication Standardization Sector (ITU-T) recommendation that describes protocols for the provision of audio-visual (A/V) communication sessions on all packet networks. H.323 provides standards for equipment, computers and services for multimedia communication across packet based networks and specifies transmission protocols for real-time video, audio and data details.


H.323 is widely used in IP based videoconferencing, Voice over Internet Protocol (VoIP) and Internet telephony. Users can communicate through the Internet and make use of a variety of products that are H.323 standard compatible.

Techopedia Explains H.323

The H.323 standard mainly depends on the Internet Engineering Task Force’s (IETF) Real-Time Control Protocol (RTCP) and Real-Time Protocol (RTP), with the utilization of various other protocols for data communication, call signaling and A/V communications.

Formally recognized in October 1996, the H.323 standard is part of H.32x, an ITU-T family of recommendations that provides multimedia communication services across various networks. These standards specify how H.323-compliant components establish calls, share compressed video and audio, attend multi unit conferences and work with non-H.323 endpoints.

H.323 defines four types of components, which, when internetworked, deliver point-to-multipoint as well as point-to-point multimedia communication services. The components are as follows:

  • Terminals: Local area network (LAN) client endpoints that deliver bi-directional, real-time multimedia communications. The H.323 terminal can be a computer or device that runs an H.323 stack and multimedia applications.
  • Gateways: Used to connect two distinct networks, the H.323 gateway provides connectivity between H.323 and non-H.323 networks. This distinct network connectivity is established by translating protocols intended for call setup and release, transforming media formats in between various networks and switching details between networks that are interconnected by the gateway.
  • Gatekeepers: Considered the most vital H.323 component, the gatekeeper serves as the core point for every call inside its zone, while providing registered H.323 endpoints with call control services. In H.323 networks, gatekeepers are optional. However, if they are available in the network, the endpoints must definitely use their services.
  • Multipoint Control Units (MCU): Deliver support for conferencing three or more H.323 endpoints or terminals. Each terminal participating in a conference sets up a MCU connection.

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Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.