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(communications, standard)
The ITU-T standard for sending voice (audio) and video using IP on a LAN without QoS.

H.323 includes Q.931 for call setup, H.225 for call signalling, H.245 for exchanging terminal capabilities, RTP/RTCP for packet streaming, G.711/G.712 for CODECs, and several other protcols, many of which need to be negotiated to setup a simple voice call.

The complexity of H.323 has lead to the IETF proposing the simpler alternatives SIP and MGCP/Megaco.


An ITU standard for real-time voice and videoconferencing over packet networks, including LANs, WANs and the Internet. Although H.323 is a very comprehensive standard that supports voice, video, data, application sharing and whiteboarding, the parts relating to audio protocols have been widely used for IP telephony applications.

H.323 defines various elements including media gateways for conversion to packets, gatekeepers for call control and multipoint control units (MCUs) for conferencing. Following are the various protocols referenced under the H.323 umbrella. See videoconferencing, codec, H.225, H.245, IP telephony, gatekeeper, SIP and MGCP/MEGACO.

Standard Function

   G.711      Audio codec
   G.722      Audio codec
   G.723      Audio codec
   G.728      Audio codec
   G.729      Audio codec

   H.261      Video codec
   H.263      Video codec
   H.264      Video codec

   H.225      Call control
   H.245      Control messages
   Q.931      Connection messages
   RAS        Control channel

   T.120      Data collaboration
References in periodicals archive ?
Services include H323 and SIP support, TDM support, real time traffic analysis, a Sonus infrastructure compatible with most 3rd party vendors and web access and management of accounts.
02 Contract Notice (below OJEU threshold): The University is looking to install a state of the art flexible multi-screen presentation system that incorporates a full H323 and SIP Video conferencing system in the EPSRC Future Manufacturing Research Hub in Continuous Manufacture and Advanced Crystallisation (CMAC) which is housed in the Technology and Innovation Centre (TIC).
Mondopad Ultra offers the security features native to Windows 10 Pro and the robust collaboration features of SIP and H323.
GL also provides testing and simulation tool that is designed not only to monitor RTP and RTCP packets, but also to allow users to manually create and terminate RTP sessions, independent of call-signaling protocols such as SIP, H323, MEGACO, or MGCP.
FHF phones use SIP or H323 protocols, which means they are easy to integrate with any major VoIP telephone system.
225 RAS Control (Registro, Admision y Estado) es un protocolo de comunicaciones que permite a una estacion H323 localizar otra estacion H323 a traves de una entidad llamada Gatekeeper.
Cisco says it did have interoperability with Video Conferencing systems from the early stages but it was limited to Standard Definition SD using SIP or H323.
Asi mismo, se deben tener en cuenta los protocolos que se utilizan en el proceso de interconexion de estas redes, dentro de los cuales se encuentran: SIP, DIAMETER, H323 entre otros.
The company's products run on Sun and Linux platforms, are compatible with Cisco gateways, and support both SIP and H323 devices.
The solution also provides multivendor support for VoIP protocols, including SIP, H323, Cisco Skinny, Nortel Unistim and other proprietary protocols.
The NKU-METS Center for Corporate Learning is technology focused, with a 150-seat "smart" auditorium, three computer labs, wireless Internet access, H320 and H323 videoconferencing capabilities, and wireless audience response systems.
Orange will use a non-standard video compression technique developed at the University of Strathclyde, so the devices will not inter-operate with standard H323 video devices.