ISDN Demonstrator User’s Manual
40-400-00011, Rev. B
26
SETUP
SETUP
ACKnowledge
STATUS
STATUS
ENQuiry
TRANSfer*
TRANSfer
REJect
Typical Call Control Sequence
Figure 4 illustrates a common method for depicting a Call Control (Layer 3)
message exchange, end-to-end, for setting up and releasing a successful
call. The near-end or originating caller is shown on the left, while the far-end
or terminating caller is on the right. In this example, the Directory Number is
dialed using the keypad.
Figure 4. Call Control Message Exchange Example
When User 1 picks up the handset, the terminal sends a SETUP message to
the switch indicating the Off Hook condition (Switchhook), type of call (Bearer
Capability), the desired channel (Channel ID), the selected Call Appearance,
and the Calling Party Number.
The Called Party Number is not included, so the switch returns a SETUP
ACKnowledge message indicating the assigned channel and in-band tones
applied (Signal=Dial Tone). User 1 dials the number, which is sent in seven
consecutive INFOrmation messages (overlap send). Once the switch
determines that a valid number has been requested, it returns a CALL
PROCeeding message, which may include Display Text, showing the name
and requested number.
