Avaya Nortel Communication Server 1000 Reference page 50

Overview
Loop Start Mode
In Loop Start mode, the A and B bits meaning is:
• Transmit from LTI:A bit = 0 (tip ground on); B bit = Ringing (0=on, 1=off)
• Receive to LTI: A bit = Loop (0=open, 1=closed); B bit = 1 (no ring ground)
When a T1 channel is idle, the Lineside T1 card simulates a ground on the tip lead and –48Vdc
on the ring lead to the terminal equipment by setting its transmit A bit to 0 and transmit B bit
to 1. Accordingly, an on-hook channel on the terminal equipment simulates an open loop
toward the Lineside T1 card, causing the Lineside T1 card's receive bits to be set to A = 0 and
receive B = 1.
Incoming calls
Incoming calls to terminal equipment attached to the Lineside T1 card can originate either from
stations that are local (served by the PBX), or remote (served through the PSTN). To provide
the ringing signal to a telephone the Lineside T1 card simulates an additional 90V on the ring
lead to the terminal equipment by alternating the transmit B bit between 0 and 1 (0 during ring
on, 1 during ring off). When an incoming call is answered by the terminal equipment going off-
hook, the terminal equipment simulates tripping the ringing and shutting off ringing, causing
the Lineside T1 card's receive A bit to be changed from 0 to 1.
Outgoing calls
During outgoing calls from the terminal equipment, a channel is seized when the station goes
off-hook. This simulates a low-resistance loop across the tip and ring leads toward the Lineside
T1 card, causing the lineside T1's receive A bit to be changed from 0 to 1. This bit change
prepares the Lineside T1 to receive digits. Outward address signaling is then applied from the
terminal equipment in the form of DTMF tones or loop (interrupting) dial pulses that are signaled
by the receive A bit pulsing between 1 and 0.
Call disconnect from far end PSTN, private network or local Station
When a call is in process, the central office may disconnect the call from the CS 1000E, CS
1000M, and Meridian 1. If the Lineside T1 port is configured with the supervised analog line
(SAL) feature, the Lineside T1 card responds to the distant end disconnect message by
momentarily changing its transmit A bit to 1 and then returning it to 0. The duration of time that
the transmit A bit remains at 1 before returning to 0 depends upon the setting that was
configured using the SAL. If the terminal equipment is capable of detecting distant end
disconnect, it responds by changing the Lineside T1 card's receive A bit to 0 (open loop). The
call is now terminated and the interface is in the idle (on-hook) state.
For the Lineside T1 card to support distant end disconnect in loop start mode, the following
configuration parameters must exist:
• The Supervised Analog Line (SAL) feature must be configured for each Lineside T1
port.
50 Circuit Card Reference
Comments? infodev@avaya.com
July 2011