Nortel Networks Circuit Card - Manual (Page 580)

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