H.323
H.323 is an umbrella recommendation from the International Telecommunications Union (ITU), setting standards for multimedia communications over LANs that do not guarantee quality of service. H.323 is part of a larger series of ITU-T communications standards for voice, data, and videoconferencing.
Using H.323 standards, a network manager can restrict network bandwidth used for applications like videoconferencing.
H.323 defines four major components for a network-based communications system: terminals, gateways, gatekeepers, and multipoint control units (MCU). Voice, video, and data are all supported across this common four-part architecture.
• Terminals are the user endpoints on a LAN that support voice, video and data. H.323 terminals must also support H.245, which is used to negotiate channel usage and capabilities. Three other components are required: Q.931 for call signaling and call setup; Registration/Admission/Status, which is used to communicate with a gatekeeper; and support for sequencing audio and video packets.
• Gateways are optional in an H.323 conference. Gateways provide many services, the most common being translation between H.323 conferencing endpoints and other terminal types. Gateways are not required if connections are made to other endpoints on the same LAN.
•A gatekeeper provides call control services to registered endpoints. In many ways, an H.323 gatekeeper acts as a virtual switch, and it performs address translation and manages bandwidth. The collection of all terminals, gateways, and MCUs managed by a single gatekeeper is known as an H.323 Zone. Note that a gatekeeper is a logical entity, and can be physically included in gateways and MCUs.
•MCUs provide the capability to bring three or more parties on a single voice or video call. The MCU also provides key functions for multicast, including control over resource streaming to avoid bandwidth contention.
From H.323 basics, Network World on Convergence, 10/21/02.
Also see: H.245, SIP and session controller.
Additional resources
H.323 Information Site
Papers, presentations and other background info on the standard.
H.323 vs. SIP
Network World Convergence Newsletter, 07/03/02.
OpenH323 Project
Effort to build an open-source H.323 stack.
VoIP makes strides
Advanced features gain support and first H.323 to SIP interconnections demonstrated, but more work needs to be done. Network World, 01/28/02.
Convergence research center
Latest news, analysis and resource links from Network World Fusion.
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