Nortel Circuit Card Installation Manual page 580

Page 580 of 906
Figure 120
Ground start call connection sequence – incoming call from CO/FX/WATS
A
Near end
System
State
Idle
Trunk seizure
Call presented to
console loop key
Console answers
2-way voice
connection
B goes on hook
Idle
A goes on hook
Idle
553-3001-211 Standard 3.00
NT8D14 Universal Trunk card
Signal/direction
High-
resistance
Tip open/
loop
battery on ring
Ground on tip
Low-resistance loop
Ground on tip/
battery on ring
Tip open/
battery on ring
High-resistance loop
High-resistance loop
Tip open/
battery on ring
August 2005
Far end
CO
CO grounds tip. Near end detects the ground
and makes the trunk busy to all outgoing calls.
Ringing
Ringing is superimposed on battery by the
CO.
When console answers, near end places a
low-resistance loop across the tip and ring.
When CO detects change to low-resistance
loop, it removes ringing. Some COs may
reverse battery and ground on tip and ring.
If far end disconnects first, CO removes
ground from tip. If battery and ground were
reversed when call was established, battery
is removed from tip and restored to ring.
Near end detects drop in loop current and
opens loop.
If near end disconnects first, it opens the
loop, waits 50 ms, and then reconnects the
ground detector.
CO detects drop in loop current and
removes ground from tip. If battery and
ground were reversed when call was
established, battery is removed from tip and
restored to ring.
B
Remarks
553-AAA1134