Nortel TFC002 Manual page 29

Equipment specification and operation Page 21 of 64
Flash signal
When the CAS attendant presses the Signal Remote (SIG REM) key on the
console, a timed flash (on hook) signal is sent to the Remote site. The flash
signal changes the resistance across the tip and ring leads from low (off hook)
to high (on hook) resistance for a timed interval. The flash signal should be
600 ms (±200 ms), with the preferred signal being 512 ms.
After the CAS attendant has pressed the SIG REM key, a Digitone receiver
at the Remote end is connected to the RLT, and a dial tone is sent to the
attendant as confirmation that an idle receiver has been connected. Digits
dialed after receiving the dial tone are outpulsed as soon as an outpulser is
available.
When the CAS attendant wants to release from a prior request—for example,
a call extended to a busy telephone—the Release Destination (RLS DEST)
key on the console is pressed. The operation of this key sends a timed flash to
the Remote site and connects the attendant to the original calling party.
Disconnect
The CO trunk at the Main site interprets the removal of ground from the tip
lead and the removal of the –48-V battery from the ring lead that persists for
more than 1 second as a disconnect signal from the RLT. After interpreting a
disconnect from the Remote site, the CO trunk disconnects from the CAS
attendant and removes the loop across the tip and ring leads, which acts as a
disconnect supervision.
When the CAS attendant disconnects, the resistance of 800 Ω or less applied
to the tip and ring leads at the CO trunk changes to 20-K Ω or more, which is
an on hook signal to the RLT at the Remote site.
Centralized Attendant Service Description and engineering