Nortel Networks Circuit Card - Manual (Page 169)

NT1R20 Off-Premise Station Analog Line card Page 169 of 906
Circuit Card Description and Installation
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
Table 68).
Table 68
Call connection sequence—near-end station receiving call (Part 1 of 2)
State
Signal / Direction
Far-end / Near-end
Remarks
Line card unit idle Group on tip, battery on ring
High resistance loop 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.
Incoming call Ringing The system applies 20 Hz ringing to ring
lead.
Near-end station
off-hook Low resistance loop
Two-way voice
connection The system detects increase in loop
current, tips ringing, and put call through
to near-end station.
Near end station
hangs up first High-resistance loop If near end station hangs-up first, the
line card detects the drop in loop
current.
Line card unit idle Group on tip, battery on ring
High resistance loop Line card unit is ready for the next call.