Nortel Circuit Card 311 Reference page 139

The operation of each unit is configured in software and is implemented in
the card through software download messages. When the OPS analog
line card unit is idle, it provides a ground on the tip lead and – 48 V dc on
the ring lead. The on-hook telephone presents a high impedance toward
the line interface unit on the card.
The applications, features, and signaling arrangements for each unit on
the NT1R20 OPS Analog Line Card are assigned through the Single-line
Telephone Administration program LD 10 and/or jumper strap settings on
the card.
The operation of each unit is configured in software and implemented in
the card through software download messages. When the NT1R20 OPS
Analog Line Card unit is idle, it provides a ground on the tip lead and –48
V dc on the ring lead. The on-hook telephone presents a high impedance
toward the line interface unit on the card.
Incoming calls
Incoming calls to a telephone connected to the NT1R20 OPS analog line
card originate from stations that can be local (served by the PBX) or remote
(served through the public switched telephone network). The alerting
signal to telephones is 20 Hz (nominal) ringing. When an incoming call
is answered, ringing is tripped as the telephone goes off-hook, placing
a low-resistance dc loop across the tip and ring leads toward the OPS
analog line card. (see
receiving call" (page
Table 68
Call connection sequence-near-end station receiving call
Signal / Direction
State Far-end / Near-end
Line card unit idle Group on tip, battery on ring High
resistance loop
Incoming call Ringing
Near-end station Low resistance loop
off-hook
Copyright © 2003-2008, Nortel Networks
.
Table 68 "Call connection sequence-near-end station
139)).
Remarks
No battery current drawn.
Far-end station goes off-hook and
addresses (dials-up) the near-end station.
The system receives the incoming call on a
trunk and determine the TN.
The system applies 20 Hz ringing to ring
lead.
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Operation 139