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H.323

H.323. Recommended by ITU-T for implementing packet-based multimedia conferencing over LAN that cannot guarantee QoS.

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H.323

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  1. H.323 • Recommended by ITU-T for implementing packet-based multimedia conferencing over LAN that cannot guarantee QoS. • Specifying protocols, methods and network elements to establish point-to-point multimedia connections between two endpoints and multipoint conferences with three or more parties.

  2. Network elements: • Terminals: a device that includes a signaling end point which supports one or more users. • H.323 call model is executed between two terminals, a terminal and a gatekeeper, or a terminal and a gateway. • Gatekeepers (GK): the brain of an H.323 zone. • An H.323 zone includes terminals, gateways, and MCUs managed by one gatekeeper. Book keeping, access control. • Multicast units (MCUs): perform one to many communications. • Gateways: offer access to different types of segments.

  3. H.323 functions are in three areas: • Registration with a gatekeeper with the registration, authentication, and status (RAS) protocol (H.225.0) • Over UDP • Call signaling using H.225.0 • Over TCP • Logical channel capabilities negotiation (media control) with H.245. • Over TCP

  4. H.323 call models: • Many variations • Directed routed model • Gatekeeper routed model • Five phases: • Call setup • Initial communication between endpoints and terminal capability • Establishment of audio/visual communication between endpoints • Request and negotiation of call services • Call termination

  5. H.323 QoS: RSVP • transportQoS field in the ARQ RAS. • Telephony Features • Call forwarding, call waiting, three-way calling, call trace, etc. • H.323 allows call re-direction. • Protocol robustness • TCP is reliable, but connection maintenance can cause problems. • Performance issues: • Large call setup time (multiple round trips), a new fast connect procedure has been proposed. • GK routed calls also have scalability problems.

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