Nortel Networks 553-3001-211 manual State, Signal/direction

NT8D14 Universal Trunk card Page 563 of 894

Figure 113

Loop start call connection sequence – incoming call from CO/FX/WATS

A

Near end

Meridian

1

Far end

CO

B

State

Idle

Trunk seizure

Call presented to console loop key

Console answers

2-way voice connection

A goes on hook

Idle

B goes on hook

Idle

Signal/direction

	Ground
High-	on tip/
resistance	battery
loop	on ring
	Ringing

Low-resistance loop

Ground on tip/ battery on ring

High-resistance loop

Ground on tip/ battery on ring

Ground on tip/ battery on ring and dial tone

High-resistance loop

Remarks

Ringing signal is superimposed on battery by the CO upon seizure.

Near end detects the ringing signal, makes the trunk circuit busy to all other calls, and presents the call to an idle console loop key.

When attendant presses a loop key to answer the call, the near end places a low-resistance loop between tip and ring and removes the ring and ground detectors from the circuit.

CO detects the change in loop resistance and removes the ringing signal. Normal battery and ground will remain. However, some COs may reverse battery and ground.

If near end disconnects first, it opens the loop, waits at least 50 ms, and then reconnects the ring and ground detectors.

Normally, no disconnection signal is returned by the CO; normal battery and ground will remain. However, if battery and ground were reversed when call was established, normal battery would be restored at this time.

If far end goes on hook first, CO sends dial (or busy) tone after timeout. CO also restores normal battery and ground if they had been reversed when the call was established.

All tones and any battery/ground reversal are ignored by the near end.

Near end restores high-resistance loop when terminal A goes on hook.

553-6240

Circuit Card Description and Installation