Avaya Nortel Communication Server 1000 Reference page 52

Overview
Far end disconnects by dropping loop current and Lineside
T1 card changes Transmit A bit to 1 momentarily.
Terminal equipment responds causing Receive A bit to
change to 0.
Lineside T1 responds by changing its Transmit A bit to 0. Call
is terminated and set to idle state.
Call disconnect from terminal equipment:
Steady state (call in progress)
Terminal equipment goes on-hook causing the Receive A bit
to change to 0. Call is terminated and set to idle state.
Ground Start Mode
In Ground Start mode, the A and B bits meaning is:
• 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.
Incoming Calls
Incoming calls to terminal equipment that is connected to the Lineside T1 card can originate
either from stations that are local (served by the PBX), or remote (served through the public
switched telephone network). To provide the ringing signal to the terminal equipment the
Lineside T1 card simulates the 90V ring signal on the ring lead by alternating the transmit B
bit between 0 and 1 (0 during ring on, 1 during ring off), and ground on the tip lead by setting
the transmit A bit to 0. When an incoming call is answered (by the terminal equipment going
off-hook), the terminal equipment simulates tripping the ringing and shutting off ringing by
causing the lineside T1's receive A bit to change from 0 to 1. The Lineside T1 card responds
to this message by simulating loop closure by holding the transmit B bit constant at 1.
Outgoing Calls
During outgoing calls from the terminal equipment, a channel is seized when the terminal
equipment goes off-hook, simulating a ground to the ring lead toward the Lineside T1 card by
causing the lineside T1's receive B bit to change from 1 to 0. In turn, the Lineside T1 card
simulates grounding its tip lead by changing the transmit A bit to 0. The terminal equipment
responds to this message by removing the ring ground (lineside T1's receive B bit is changed
52 Circuit Card Reference
State
Comments? infodev@avaya.com
Transmit Receive
A B A B
1 1 1 1
1 1 0 1
0 1 0 1
0 1 1 1
0 1 0 1
July 2011