Nortel Circuit Card Installation Manual page 575

Figure 116
Loop start call connection sequence – incoming call from CO/FX/WATS
A
Near end
Meridian
1
State
High-
resistance
loop
Idle
Trunk seizure
Call presented to
console loop key
Low-resistance loop
Console answers
2-way voice
connection
High-resistance loop
A goes on hook
Idle
B goes on hook
High-resistance loop
Idle
Far end
Signal/direction
Ground
on tip/
battery
on ring
Ringing
Ground on tip/
battery on ring
Ground on tip/
battery on ring
Ground on tip/
battery on ring
and dial tone
NT8D14 Universal Trunk card
B
CO
Remarks
Ringing signal is superimposed on battery by the CO
upon seizure.
Near end detects the ringing signal, makes the trunk
circuit busy to all other calls, and presents the call to
an idle console loop key.
When attendant presses a loop key to answer the call,
the near end places a low-resistance loop between tip
and ring and removes the ring and ground detectors
from the circuit.
CO detects the change in loop resistance and removes
the ringing signal. Normal battery and ground will
remain. However, some COs may reverse battery and
ground.
If near end disconnects first, it opens the loop, waits at
least 50 ms, and then reconnects the ring and ground
detectors.
Normally, no disconnection signal is returned by the CO;
normal battery and ground will remain. However, if battery
and ground were reversed when call was established,
normal battery would be restored at this time.
If far end goes on hook first, CO sends dial (or busy) tone
after timeout. CO also restores normal battery and ground
if they had been reversed when the call was established.
All tones and any battery/ground reversal are ignored by
the near end.
Near end restores high-resistance loop when terminal A
goes on hook.
Circuit Card
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553-6240
Description and Installation