Cisco Cisco IOS Software Release 12.2(15)T Guide Du Développeur
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Cisco Gatekeeper External Interface Reference, Version 4.2
Cisco IOS Release 12.2(15)T
Chapter 1 Overview of H.323
Gatekeepers
Gatekeepers
Gatekeepers are optional nodes that manage other nodes in an H.323 network. Other nodes communicate
with the gatekeeper using the RAS protocol. A gatekeeper is not required in an H.323 network, but it
must be used if one is present.
with the gatekeeper using the RAS protocol. A gatekeeper is not required in an H.323 network, but it
must be used if one is present.
The H.323 nodes attempt to register with a gatekeeper on startup. When an H.323 node wants to
communicate with another endpoint, it requests admission to the call, using a symbolic alias for the
endpoint name such as an E.164 (ITU-T recommendation for international telecommunication
numbering) address or an e-mail ID. If the gatekeeper decides the call can proceed, it returns a
destination IP address to the originating H.323 node. This IP address can be the actual address of the
target endpoint or it can be an intermediate address. Finally, a gatekeeper and its registered endpoints
exchange status information.
communicate with another endpoint, it requests admission to the call, using a symbolic alias for the
endpoint name such as an E.164 (ITU-T recommendation for international telecommunication
numbering) address or an e-mail ID. If the gatekeeper decides the call can proceed, it returns a
destination IP address to the originating H.323 node. This IP address can be the actual address of the
target endpoint or it can be an intermediate address. Finally, a gatekeeper and its registered endpoints
exchange status information.
Gatekeeper Zones
H.323 endpoints are grouped together in zones. Each zone has one gatekeeper that manages all the
endpoints in the zone. A zone is an administrative convenience similar to a DNS domain. Gatekeeper
zones are normally set up to correspond to geographic zones.
endpoints in the zone. A zone is an administrative convenience similar to a DNS domain. Gatekeeper
zones are normally set up to correspond to geographic zones.
MCUs
An MCU is an endpoint on the LAN that provides the capability for three or more terminals and gateways
to participate in a multipoint conference. It controls and mixes video, audio, and data from terminals to
create a robust video conference. An MCU can also connect two terminals in a point-to-point conference
that can later develop into a multipoint conference.
to participate in a multipoint conference. It controls and mixes video, audio, and data from terminals to
create a robust video conference. An MCU can also connect two terminals in a point-to-point conference
that can later develop into a multipoint conference.
Note
Some terminals have limited multipoint-control built into them. These terminals might not require an
MCU with all the functionality mentioned previously.
MCU with all the functionality mentioned previously.
Gateways
An H.323 gateway can provide an interface between H.323 and the Public Switched Telephone Network
(PSTN), H.320 terminals, V.70 terminals, H.324 terminals, and other speech terminals. It provides
standard interfaces to the PSTN, processes the voice and fax signals using CODECs to convert between
circuit-switched and packet formats, and works with the gatekeeper through the RAS protocol to route
calls through the network. Gateways provide translation between transmission formats, such as H.245
and H.242.
(PSTN), H.320 terminals, V.70 terminals, H.324 terminals, and other speech terminals. It provides
standard interfaces to the PSTN, processes the voice and fax signals using CODECs to convert between
circuit-switched and packet formats, and works with the gatekeeper through the RAS protocol to route
calls through the network. Gateways provide translation between transmission formats, such as H.245
and H.242.
shows a gateway between an H.323 terminal and a speech-only telephone.