Protocols - D-Link DFL-1600 User Manual

18.4. H.323 159
MCUs (Multipoint Control Units)
Terminals
A H.323 terminal is a device that is used for audio and optionally video or
data communication. For example phones, conferencing units, or software
phones (for example: NetMeeting) running on standard PCs.
Gateways
A gateway connects two dissimilar networks and translates traffic between
them. A H.323 gateway provides connectivity between H.323 networks and
non-H.323 networks such as public switched telephone networks (PSTN).
The gateway takes care of translating protocols and converting media
between the different networks. A gateway is not required for
communication between two H.323 terminals.
Gatekeepers
The Gatekeeper is a component in the H.323 system which is used for
addressing, authorization and authentication of terminals and gateways. It
can also take care of such things as bandwidth management, accounting,
billing and charging. The gatekeeper may allow calls to be placed directly
between endpoints, or it may route the call signaling through itself to
perform functions such as follow-me/find-me, forward on busy, etc. A
gatekeeper is needed when there is more then one H.323 terminal behind a
NATing firewall with only one public IP.
MCUs (Multipoint Control Units)
MCUs provide support for conferences of three or more H.323 terminals.
All H.323 terminals participating in the conference call have to establish a
connection with the MCU. The MCU then manages the calls, resources,
video and audio codecs used in the call.
18.4.3 H.323 Protocols
The different protocols used in H.323 is shortly described below:
H.225 RAS Signaling and Call Control (Setup) Signaling
The H.225 protocol is used for call signaling, that means that it's used to
establish a connection between two H.323 endpoints (terminals). This call
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