40-400-00001, Rev. A
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RECONNect ACKnowledge (AT&T)
RECONNect REJect (AT&T)
REGISTER (NI-1/NTI)*
RELease
RELease COMPlete
RESTart
RESTart ACKnowledge
RETrieve (NTI)
RETrieve ACKnowledge (NI-1/NTI)
RETrieve REJect (NI-1/NTI)
SETUP
SETUP ACKnowledge
STATUS
STATUS ENQuiry
TRANSfer*
TRANSfer REJect
Typical Call Control Sequence
Figure 5 illustrates a common method for depicting a Call Control (Layer 3) mes-
sage 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.
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 Capabil-
ity), 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.
The switch broadcasts a corresponding SETUP message to the line associated with
the dialed number, selecting a B Channel if one is available. Any terminals that
match the requested Bearer Capability, and optionally, match the address contained
in an Endpoint ID, respond to the SETUP with an ALERTing message and begin
ringing. When the switch sends an idle Call Appearance to terminals that support the
CACH option, the incoming call is also indicated visually.