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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 ?
Tenders are invited for Vvx 1500 Dual Stack Sip And H323 Busines Media Phone With Video Capabilty And Hd Voice Poe.
Since the initial deployment, Alestra has continued to leverage its Sonus network in a variety of applications, including H323 and SIP routing, PBX and IP-PBX termination, and carrier peering via TCP/IP.
For consistency, all SIP and H323 calls from the headquarters had to traverse the LinkProof 1000s primary gigabit IP links and terminate to the WinSIP and WinH323 generators at the remote branch site.
Students can rely on their cell phones, and will also have the option of using wireless SIP or H323 phones.
This contract concerns -The provision of mobile subscriptions on iphone and ipad with a summarized list is as follows Oforfait voice (excluding ipad) : oforfait DATA including SMS, MMS, can position the equipment Modem mode or connection sharing, access to Internet service on various protocols (for example, http, https, H323, Sip .
New capabilities also include SIP and H323 support and enhancements that support the implementation of high availability and disaster recovery systems.
SoftSwitchAxcess features: - Access to a managed, independent carrier grade softswitch - Optional access to a carrier grade TDM switch - Carrier class signaling and protocol conversion: SIP, H323, SS7, C7 - Collocation and high quality IP access - Unlimited route updates through an on-line system - Highest security and authentication of partner gateways and traffic flows - Full interworking with CDR generation and rating
The NexTone Multi-protocol Session Exchange (MSX) interconnects SIP and H323 VoIP networks.
Almost all protocols over IP transport layer for example: SIP, SIP-I, SIP-T, H323, MEGACO, MGCP, Diameter, LTE S1, X2, and eGTP and more can be captured and decoded for troubleshooting network problems.
By achieving Avaya compliance for our new OnDemandH323 Trunking services, we are empowering businesses to leverage their existing H323 deployments and harness the significant benefits previously available only with SIP trunking," said Albert Rodriguez, president of AGN Networks.
Avaya and AGN Networks will announce H323 Trunking compliance for Avaya Communication Manager.
It is applicable to cellular technologies such as GSM, CDMA, GPRS and UMTS, and new fixed-telephone networks based on internet protocols like H323 and SIP.