Page 52 of 906 Overview
553-3001-211 Standard 3.00 August 2005
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.
• Steady state (call in progress) 0 1 1 1
• Far end disconnects by dropping loop current and lineside T1
card changes Transmit A bit to 1 momentarily.
1 1 1 1
• Terminal equipment responds causing Receive A bit to
change to 0.
1 1 0 1
• Lineside T1 responds by changing its Transmit A bit to 0. Call
is terminated and set to idle state.
0 1 0 1
Call disconnect from terminal equipment:
• Steady state (call in progress) 0 1 1 1
• Terminal equipment goes on-hook causing the Receive A bit
to change to 0. Call is terminated and set to idle state.
0 1 0 1
Table 4
Loop Start Call Processing A/B Bit Settings (Part 2 of 2)
State
Transmit Receive
A B A B
