Nortel Meridian 1 Manual page 15

Page 10 of 44 NT5K93 Central office trunk circuit card
Supplement to 553-3011-210
Dialling
The Option 11 sends digits in the form of loop disconnect signalling or Dual
Tone Multi-frequency (DTMF) digits.
Answer
When the called party answers, the central office reverses polarity on the line.
The Option 11 interprets the polarity reversal as an answer signal.
Call placed by central office
Fastguard signal
Before applying ringing to the Option 11, the central office sends a Fastguard
signal (battery reversal) that is used to busy a trunk circuit against outgoing
calls. The NT5K18BA trunk card, however, can not detect battery reversal
in the idle state.
Ringing
The central office applies ringing to the ring wire and -50V dc to the tip wire.
The Option 11 ringing detector trips to indicate an incoming call.
Answer
The Option 11 answers the call by placing a loop between the tip and ring
leads. The central office responds by removing the ringing and reversing
battery on the tip and ring leads.
Call disconnect
Option 11 disconnect
The Option 11 disconnects the call by removing the dc loop between the tip
and ring leads. The central office responds by returning to the polarity of the
idle state.
Central office disconnect—outgoing call from Option 11
The central office sends a disconnect signal by reversing the polarity on the
tip and ring leads The Option 11 responds by releasing the call.
Central office disconnect—incoming call from central office
The central office disconnects the call by sending a clear forward signal,
which is an 800 to 1100 ms break on the tip or ring wires. The clear forward
signal is sent only on incoming calls to the Option 11 and may not always be
provided. On receipt of the signal, the Option 11 returns to the idle state.
Provisional 1.3 July 1993