Avaya S8700 Maintenance Manual page 1296

Maintenance-Object Repair Procedures
Loop Start Operation
Idle State: Tip = ground, Ring = CO Battery
Outgoing Call
1. PBX Off-Hook (Seize Message): Closes the Tip-Ring Loop CO Response:
DC loop current + Dial tone
2. PBX On-Hook (Drop Message): Open Tip-Ring loop, no loop current CO
Response: CO goes to idle state (see Note)
Incoming Call
1. CO Applies Ringing Voltage PBX Response: Detect ringing current
2. PBX Off-Hook (Answer Message): Close loop CO Response: Trip ringing,
provide loop current
3. PBX On-Hook (Drop Message): Open Tip-Ring loop, no loop current CO
Response: CO goes to idle state (see Note)
Direct Inward Dialing (DID)
1. CO Applies Ringing Voltage
PBX Response: Detect ringing current and close loop
CO Response: Send DTMF digits
PBX Response: Acknowledge of Number dialed and open loop
2. PBX Off-Hook (Answer Message): Close loop CO Response: Trip ringing,
provide loop current
3. PBX On-Hook (Drop Message): Open Tip-Ring loop, no loop current CO
Response: CO goes to idle state (see Note)
NOTE:
CO does not normally provide an On-Hook (Disconnect) signal.
8-574 Issue 1 May 2002 555-233-143