Nortel Meridian 1 Manual page 39

Page 36 of 44 Direct Dial Inward trunk card
Table 25
Summary of NT5K17BA DDI Trunk card signalling states
Signal
Idle
Seize
Dialling
Answer
Central Office disconnect
(Far End Release)
Far End Release
acknowledgement
Option 11 disconnect
(Near End Release)
Near End Release
acknowledgement
Backward Busy
Supplement to 553-3011-210
When the DDI unit detects the high impedance loop, it sends a change of state
message to the CPU. The CPU sends a release acknowledgement message
back to the DDI unit, which will respond by returning to the idle state.
Near End Release
When the Option 11 disconnects the call, the CPU sends a message to the DDI
unit, which in turn will respond by returning to the idle state. When the central
office detects the idle state, it restores the high impedance loop on the tip and
ring wires. The CPU interprets the high impedance loop as a release
acknowledgement signal from the central office.
Backward Busy or Disabled
When a DDI unit is busy or disabled, it sends a backward busy signal to the
central office. In this state, both battery and ground are removed from the tip
and ring wires.
Central Office State
High Impedance Loop
(9K ohms or greater)
Low Impedance Loop
(2.2K ohms or less)
Loop disconnect signalling or
DTMF
Low Impedance Loop
(2.2K ohms or less)
High Impedance Loop
(9K ohms or greater)
—
—
High Impedance Loop
(9K ohms or greater)
—
Provisional 1.3
Option 11 State
Ground on Tip
-50V on Ring
—
—
-50V on Tip
Ground on Ring
—
Ground on Tip
-48V on Ring
Ground on Tip
-48V on Ring
—
Open Circuit on Tip
Open Circuit on Ring
July 1993