This week, we'll discuss H.323 terminology as a primer for coming issues on videoconferencing.
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.
The first H.323 specification was approved in 1996, and subsequent versions have increased functionality. 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.
Next time, we'll cover some more basics about how video over IP works.
RELATED LINKS
Network World, 10/21/02
Steve Taylor is President of Distributed Networking Associates and Publisher/Editor-in-Chief of Webtorials.Com. For more detailed information on most of the topics discussed in this newsletter, connect to Webtorials.Com, the first Web site dedicated exclusively to market studies and technology tutorials in the Broadband Packet areas of Frame Relay, ATM, and IP.
Larry Hettick is an independent consultant, with 19 years of experience in telecommunications and data communications marketing and product management for service providers and equipment vendors. He can be reached at larry@larryhettick.com
You can reach the authors at taylor@webtorials.com or larry@larryhettick.com.
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