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

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H 323
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.


H 323

  • 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.


H 323

  • 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


H 323

  • 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


H 323

  • 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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