Avaya Definity SI Maintenance Manual page 1224

Maintenance Object Repair Procedures
LOOP START AND UK LOOP CALLING GUARDED CLEARING OPERATION
Idle State - Tip _ ground, Ring = CO Battery
A. Outgoing Call
1. PBX Off-Hook (Seize Message): Closes the Tip-Ring Loop
a. CO Response: DC loop current + Dial tone
2. PBX On-Hook (Drop Message): Open Tip-Ring loop, no loop current
a. CO Response: CO goes to idle state (see Note)
B. Incoming Call
1. CO Applies Ringing Voltage
a. PBX Response: Detect ringing current
2. PBX Off-Hook (Answer Message): Close loop
a. CO Response: Trip ringing, provide loop current
3. PBX On-Hook (Drop Message): Open Tip-Ring loop, no loop current
a. CO Response: CO goes to idle state (see Note)
NOTE:
Except for the Netherlands Loop Start and UK Loop Calling Guarded
Clearing trunks, CO does not normally provide an On-Hook (Disconnect)
signal.
GROUND START AND UK EARTH CALLING OPERATION
Idle state - Tip _ open, Ring = CO Battery
A. Outgoing Call
1. PBX Off-Hook (Seize Message): Places ground on Ring
a. CO Response: Places ground on Tip
b. PBX Response: close the loop
c. CO Response: provide loop current
d. PBX response: dial out digits
2. PBX On-Hook first (Drop Message): Open the Tip-Ring Loop, no loop
current
a. CO Response: Open circuit on Tip
3. CO On-Hook first (Disconnect): Open circuit on Tip, no loop current.
a. PBX Response: Open Tip-Ring loop
10-438 Issue 4 May 2002 555-233-123