Instruction manual

FUNCTIONAL DESCRIPTION
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The OS checks a message directory to determine which task (i.e., software module)
is to receive the message.
A function of the OS referred to as the “transformer”
determines it has a message for the Station Call Processing task and queues the
message in RAM.
The Station Call Processing task retrieves its message and interprets it as a call
origination. The task determines whether there is an idle call appearance button
(System Access button) on the called voice terminal. If so, two available time slots
are reserved for the connection.
The task sends downlink messages to the port circuit via the OS. The messages
instruct the port circuit to listen for dial tone on a specified time slot and to light the
call appearance status LED on the terminal.
When the user dials the first digit, the port circuit determines the digit dialed. It then
listens to appropriate time slots on the TDM bus for the two tones used to generate
an equivalent DTMF signal.
It then removes dial tone and feeds the DTMF signal
back to the user until the user releases the button.
The port circuit sends an up-link message with each digit dialed to the OS that routes
them to the Dial Plan Manager (DPM).
The DPM collects the dialed digits and determines that the call is a station-to-station
call.
When the DPM collects enough digits to identify an extension number it stops
collecting digits.
Note:
If the extension number dialed is invalid, the DPM sends a down-link
message to the port circuit instructing it to listen to time slot 07
(Reorder Tone) that is then heard by the user. Go to Step 18.
A down-link message is sent to the originating port instructing it to listen to time slot
06 (busy) or 08 (ringing), as appropriate. Go to Step 18 for Busy Tone or an
unanswered call.
Station Call Processing sends a down-link message to the station port circuit pack
associated with the called extension to turn on the ringer of the terminal, and to flash
the call appearance LED.
When the called party lifts the receiver, the associated port circuit pack controller
sends a off-hook message to the OS as before.
The Station Call Processing task, when it receives the message interprets the off-
hook message as an answer.
The task sends a down-link message to the called port circuit to turn off the ringer
and to change the flashing LED to steadily lighted.
Down-link messages are sent to the port circuits assigning talk and listen time slots
for the connection.
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