R2511-HP MSR Router Series Voice Configuration Guide(V5)

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Figure 68 Gatekeeper-routed call signaling
Call setup
After receiving the ACF message from the gatekeeper, the calling endpoint sends call signaling to set up
a call. In a direct call signaling for example, the calling endpoint first sends a Setup message to the
called endpoint requesting for a connection.
Call proceeding
After receiving the Setup message, the called endpoint replies with a Call Proceeding message. However,
it might not send this message.
Alerting
Then the called endpoint might send an Alerting message to the calling endpoint, indicating its status (for
example, ringing). The endpoint might not send this message.
Connection
If the called endpoint accepts the call, it must send a Connect message.
Capability negotiation
After the calling endpoint receives the connect message, an H.245 control signaling channel is
established to control the media session between the endpoints. First, the two endpoints exchange
information on their capabilities, such as media format.