Nortel Networks 553-3001-211 manual Ground Start Mode, Call disconnect from terminal equipment

Page 50 of 894	Overview
Table 3
Loop Start Call Processing A/B Bit Settings (Part 2 of 2)
		Transmit		Receive
State		A	B	A	B
• Steady state (call in progress)		0	1	1	1
• Far end disconnects by dropping loop current and lineside T1		1	1	1	1
card changes Transmit A bit to 1 momentarily.
• Terminal equipment responds causing Receive A bit to		1	1	0	1
change to 0.
• Lineside T1 responds by changing its Transmit A bit to 0. Call		0	1	0	1
is terminated and set to idle state.
Call disconnect from terminal equipment:
• Steady state (call in progress)		0	1	1	1
• Terminal equipment goes on-hook causing the Receive A bit		0	1	0	1
to change to 0. Call is terminated and set to idle state.

Ground Start Mode

In ground start mode, the A and B bits have the following meaning:

Transmit from LTI:A bit = Tip ground (0=grounded, 1=not grounded)

B bit = Ringing (0=on, 1=off)

Receive to LTI: A bit = Loop (0=open, 1=closed)

B bit = Ring ground (0=grounded, 1=not grounded)

When a T1 channel is idle, the lineside T1 card simulates a ground on the tip lead and -48V dc on the ring lead to the terminal equipment by setting the transmit A bit to 1 and transmit B bit to 1. Accordingly, an on-hook telephone simulates an open loop toward the lineside T1 card, causing the lineside T1 card’s receive bits to be set to A = 0 and B = 1.

553-3001-211 Standard 2.00 September 2004