h.323 recommended by itu-t for implementing packet-based multimedia conferencing over lan that...
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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.
• 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 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 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 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.