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Basic Troubleshooting and Repair
Table 55: A-B Bit Signaling Example (T1/CO)
State
Transmit Receive
A B A B
Outgoing call - Basic Operation
Idle state 0 1 1 *
PBX grounds ring (wait for dial tone) 0 0 1 *
CO ground tip (dial tone applied) 0 0 0 *
PBX closes loop and removes ring ground 1 1 0 *
Dial pulsing DP 1 0 *
Completion of dialing 1 1 0 *
Incoming call - Basic Operation
Idle state 0 1 1 *
CO ground tip (interval between ringing) 0 1 0 1
CO ground tip (during ringing application) 0 1 0 0
PBX presents call 0 1 0 1
PBX answers call 1 1 0 *
Talking state 1 1 0 *
CO disconnects
Talking state 1 1 0 *
CO removes tip ground (far end hangs up) 1 1 1 *
PBX opens loop (idle) 0 1 1 *
PBX disconnects
Talking state 1 1 0 *
PBX opens loop (near end hangs up) 0 1 0 *
CO removes tip ground (idle) 0 1 1 *