Outgoing Calls; Off-Premise Station Application - Nortel Enterprise 1000 Reference Manual

(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 towards the OPS analog line card.

Outgoing calls

For outgoing calls from a telephone, a line unit is seized when the telephone
goes off-hook, placing a low-resistance loop across the tip and ring leads
towards the OPS analog line card. When the card detects the low-resistance
loop, it prepares to receive digits. When the Succession CSE 1000 is ready to
receive digits, it returns a dial tone. Outward address signaling is then applied
from the telephone in the form of loop (interrupting) dial pulses or DTMF
tones.

Off-premise Station application

The NT1R20 Off-Premise Station (OPS) Analog Line Card is designed
primarily to provide an interface for off-premise station lines. An OPS line
serves a terminal – usually, but not exclusively, a telephone set – remote from
the PBX either within the same serving area as the local office, or through a
distant office. The line is not switched at these offices; however, depending
on the facilities used, the local office serving the OPS station can provide line
functions such as battery and ringing. Facilities are generally provided by the
local exchange carrier (usually, OPS pairs are in the same cable as the PBX-
CO trunks).
Succession Communication Server for Enterprise 1000 Circuit Card Reference Guide
Analog line cards Page 221 of 236