Cisco Cisco IPS 4255 Sensor 백서

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Figure 3. Basic Constituents of a H.323 Call

Figure 3 represents a basic message sequence and the constituents of an H.323 call. The general approach to starting a call is to send a mandatory

admission request on the RAS channel, followed by an initial setup message on a reliable channel transport address (this address may have been

returned in the admission confirmation message, or may have been known to the calling terminal). As a result of this initial message, a call setup

sequence commences based on H.225 call signaling operations. The sequence is complete when in the “Connect” message, the terminal receives a

reliable transport address on which to send H.245 control messages.

Note: A reliable transport address is used for call setup for the terminal-to-terminal case, and also for the gatekeeper-mediated case. The reliable call

signaling connection is kept active until a “Release Complete” message is received for all active calls signaled over the call-signaling channel.

Figures 4 and 5 depict the message sequence of a normal inter- and intra-zone call-message sequence.