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Cisco ATA 186 and Cisco ATA 188 Analog Telephone Adaptor Administrator’s Guide (H.323)
OL-4008-01
Chapter 1 Cisco Analog Telephone Adaptor Overview
H.323 Overview
Components that the H.323 standard employs include a system of interconnected voice terminals,
gateways, gatekeepers, multipoint control units (MCUs), and proxy servers. Voice terminals provide
point-to-point and point-to-multipoint conference capability for audio, video, and data. Voice gateways
interconnect the packetized IP network to the PSTN or ISDN network. Gatekeepers provide admission
control and address translation services for H.323 voice terminals and gateways. MCUs enable two or
more gateways to engage in point-to-point or point-to-multipoint audio or video conferences.
This section contains descriptions of the following H.323 components:
• H.323 Terminals, page 1-3
• H.323 Gateways, page 1-3
• H.323 Gatekeepers, page 1-4
• H.323 MCUs, page 1-4
• H.323 Proxy Server, page 1-4
Figure 1-4 H.323 Architecture
H.323 Terminals
Voice terminals in an H.323 network must feature system control units, media transmission capabilities,
audio codecs, and network interfaces suitable for transmitting and receiving packetized data.
H.323 Gateways
H.323 gateways feature a mixture of characteristics of both standard Switched Circuit Network (SCN)
access points and H.323 access points. Gateways perform the translation of audio, video, and data
transmission formats as well as interacting with communications systems and various protocols. A
primary responsibility of an H.323 gateway is the call setup and teardown necessary to complete a call
to and from a packetized IP network and a standard switched network.
Note Gateways are necessary in an H.323 system to connect calls over a packetized IP network to a switched
circuit network such as the PSTN.
H.323
Network
Terminal
Terminal
H.323 Gatekeeper
H.323 Gateway
Cisco ATA
Analog Phone
Analog Phone
Multipoint Control
Unit (MCU)
CSN/PSTN
72858
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