Nortel Networks 1000 - Manual (Page 37)

Line cards 37
•
Idle (on-hook)
• Incoming calls
• Outgoing calls
•
Calls disconnected by the CO
•
Calls disconnected by the telephone
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 has been configured with the supervised analog line (SAL) feature,
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
.