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CO-TRK (Analog CO Trunk)
Issue 1 June 2005 837
Ground Start Operation
Idle state: Tip = open, Ring = CO Battery
Outgoing Call:
1. PBX Off-Hook (Seize message): Places ground on Ring
CO response: Places ground on Tip
PBX response: Close the loop
CO response: Provide loop current
PBX response: Dial out digits
2. PBX On-Hook first (Drop message): Open the Tip-Ring Loop, no loop current
CO response: Open circuit on Tip
3. CO On-Hook first (Disconnect): Open circuit on Tip, no loop current
PBX response: Open Tip-Ring loop
Incoming Call:
1. CO Off-Hook (Seizure): CO applies ground on Tip and applies ringing voltage to the Ring
lead.
PBX response: Make trunk busy for outgoing calls
2. CO Ringing: CO applies ringing voltage to the Ring lead.
PBX response: Detect ringing, ring destination (Attendant, hunt group, etc.)
3. PBX Off-Hook (Answer message): Close loop
CO response: Trip ringing, provide loop current
4. PBX On-Hook first (Drop message): Open the Tip-Ring Loop, no loop current
CO response: Open circuit on Tip
5. CO On-Hook first (Disconnect): Open circuit on Tip, no loop current