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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.
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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 ?
Early adopters of voice over IP (VoIP) technology purchased solutions based on the H.323 Protocol. Today's VoIP buyers tend to favor solutions that are based on the SIP (Session Initiation Protocol) standard.
When evaluating a voice over Internet protocol (VoIP) solution, the option of using an "intelligent" phone (usually associated with the SIP or H.323 protocol) instead of the usual stimulus-controlled business phone should be considered.
Levin, who was recently appointed as ITU-T Editor of Annex O for work on Internet technologies complementary to H.323, continues, "As a pioneer and leader in the development and implementation of the H.323 Protocol, RADVision has tremendous know how to contribute to clarifying the relationship between the two protocols.
RADVISION (Nasdaq:RVSN), an industry leader in providing a wide range of development solutions for voice, video, and data collaboration over IP and 3G, recently announced the general availability of its new H.323 Protocol Toolkit version 4.2.
The gateway solutions are all H.323 protocol stack compliant.
Network Instruments, LLC, Minneapolis, has launched Observer 6.2, a robust, low-cost protocol analyzer and the first traffic management and troubleshooting tool for shared and switched environments to offer Voice over IP (VoIP) H.323 protocol decoding.
Calista's DPCP protocol is unique in that it can control a wide variety of digital phones while also interoperating with the standards-based Ethernet H.323 protocol.
In June, elemedia became the first software vendor to offer access to the binary code for its leading-edge H.323 protocol stack including Real Time Protocol (RTP) Version 2 -- at no cost to industry researchers and developers.
The new platform provides an integrated high-speed, on-board Ethernet network interface controller (NIC), and on-board support of the H.323 protocol stack.
Characteristics of IP-based protocol framework, TCP- and UDP-based H.323 protocols are expected to coexist during the next couple of years.
ProLab 3.5 features the latest versions of the SIP and H.323 protocols, enabling the testing of advanced features that are enabled by recent modifications to the protocol.
The group advocates interoperability and certification based on H.323 protocols. However, the Softswitch Consortium also promotes interoperability based on the Session Initiation Protocol (SIP), the Media Gateway Control Protocol (MGCP), and Real-time Transport Protocol (RTP).