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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.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)


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
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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.
The following disulfide bridges were identified: intrachain [Cys(L23)-Cys(L88), Cys(L134) Cys(L194), Cys(H22)-Cys(H96), Cys (H146)-Cys(H202), Cys(H263)-Cys(H323), Cys(H369)-Cys(H427)] and interchain [Cys(L214)-Cys(H222), Cys(H228)-Cys(H228), Cys(H231)-Cys(H231)].
Mondopad Ultra offers the security features native to Windows 10 Pro and the robust collaboration features of SIP and H323. As conference rooms, classrooms and collaboration environments evolve and change, Mondopad offers the cross-platform, future-proof and legacy compatibility you'll need.
"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.
H323 and 449 within the LBD of PPAR[gamma] are required for the binding and activation by rosiglitazone but are not required by AGP.
"H323, SIP and H264 are well known video standards the industry is standardising on.
FHF phones use SIP or H323 protocols, which means they are easy to integrate with any major VoIP telephone system.