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NT8D14 Universal Trunk card Page 563 of 894
Circuit Card Description and Installation
Figure 113
Loop start call connection sequence – incoming call from CO/FX/WATS
A
State
Idle
Idle
Trunk seizure
Idle
B goes on hook
A goes on hook
RemarksSignal/direction
Near end
Meridian
1
B
Far end
CO
High-resistance loop
High-resistance loop
High-
resistance
loop
Ground
on tip/
battery
on ring
Ground on tip/
battery on ring
Ground on tip/
battery on ring
Ground on tip/
battery on ring
and dial tone
Low-resistance loop
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.
Ringing signal is superimposed on battery by the CO
upon seizure.
2-way voice
connection
Ringing
Console answers
Call presented to
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.
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.
If near end disconnects first, it opens the loop, waits at
least 50 ms, and then reconnects the ring and ground
detectors.
Near end restores high-resistance loop when terminal A
goes on hook.
553-6240