Chapter 1
Using the Cisco Voice Gateway 200
Voice over IP Overview
1-4
Software Configuration Guide for the Cisco VG200
78-10322-02
Figure 1-2
The H.323 Standard
H.323 endpoints can communicate among each other without the intervention of
any other devices, however to connect them to the PSTN, to manage call setup and
network bandwidth, and to simplify administration, the following devices are
often used:
•
H.323 gateway—Connects H.323 devices to POTS devices on the PSTN
•
H.323 gatekeeper—Manages network bandwidth and provides a central point
for call administration
•
H.323 proxy—An H.323 endpoint that acts as an intermediary between H.323
endpoints and other IP telephony devices
To standardize communication among these devices and endpoints, H.323 utilizes
the following protocols:
•
H.245—Used to negotiate channel usage and capabilities
•
H.225—Used for call signaling and call setup
•
Registration, Admission and Status (RAS)—Used to communicate with the
H.323 gatekeeper
•
Real-Time Protocol/Real-Time Control Protocol (RTP/RTCP)—Used to
create and transmit audio packets on the IP data network
POTS phones
H.323 end point
PSTN
H.323 Gateway
H.323 Gatekeeper
Simple IP
telephony devices
H.323 Proxy
TCP/IP network
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