Panasonic KX-TD500 System Reference Manual page 271

7.00 Calling Party Control (CPC)
Signal Detection
Description
CPC (Calling Party Control) signal is the on-hook
indication (disconnect signal) sent through the CO
line when either calling or called party goes on-
hook.
To support efficient utilization of the CO lines, the
system monitors the status of the CO lines, and
when CPC signal is detected, the system
disconnects the CO lines connected compulsorily.
In default mode, CPC signal detection works on
incoming CO calls, and does not work on outgoing
CO calls (except once they are placed on hold or
consultation hold).
In this case, if the extension user remains off-hook
after the completion of an outgoing CO call, the
system does not release all the switches used to
establish the connection, and a CO line connected
will continue to be seized by the extension user
ineffectively.
To prevent the extension users from such invalid
seizure of CO lines, it is administrable to make
CPC signal detection effect on outgoing CO calls
by using CPC command at dumb programming
mode.
This feature is assignable on a CO line basis.
Refer to Section 11-C-42.00 "CPC Signal Detect
Timing (CPC)" for further information.
Programming
System Programming
"Trunk-CO Line", CPC Detection
"CPC Signal Detect Timing
(CPC)"
Conditions
Some switching system of the central office may
send CPC-like signal in dialing sequence and the
attempt of making a call may be terminated.
If your switching system does not send CPC-like
signal in dialing sequence, we recommend to
make CPC signal detection work on outgoing CO
calls.
CPC signal detection can be assigned to
incoming CO calls only or both on incoming and
outgoing CO calls. If CPC signal detection is
assigned to outgoing CO calls only, it does not
function.
3-F-11
Reference
VT Dumb
10-F-1.00 11-C-20.00
— 11-C-42.00