Nortel Circuit Card, Installation Manual, Page: 47 / 908

Overview Page 47 of 906
Circuit Card Description and Installation
Figure 8
Battery reversal answer and disconnect supervision sequence
System
High-
resistance
loop
Line card unit idle
(2-way voice
connection)
Remarks
Ground on tip/
battery on ring
Signal/direction State
Ground on tip/
battery on ring
High-
resistance
loop
Ground on tip/
battery on ring
Far-end station
on hook
Near-end station
on hook
If near-end station hangs up first, a high-resistance loop is
presented to the system.
If far-end station hangs up first, the system detects
disconnect signalling from the far end, removes timeslot
assignments, and restores normal ground/battery polarity
to the near-end station.
No battery current drawn.
Near-end station goes off hook. Battery current is drawn
causing detection of off-hook state. The system
determines unit terminal number (TN) and assigns
message timeslots.
Low-resistance loop
Dial tone is applied to the near-end station from the
system.
Call request
Dial tone
Addressing signals
Outpulsing Near-end station dials number (loop pulsing or DTMF
tones).
Dial tone removed
The system detects start of dialing and removes dial tone.
Ringback (or busy)
The system decodes addressing, routes call, and supplies
ringback tone to near-end station if far-end station is on
hook. (Busy tone supplied if far-end station is busy.)
When call is answered (either absolute or assumed
answer, as programmed), ringback tone is removed, call
is cut through to far-end station, and battery is reversed
to near-end station for duration of call.
The system detects drop in loop current, removes timeslot
assignments, sends disconnect signal to far-end station,
and restores normal ground/battery polarity to the near-
end station. Line card unit is then ready for the next call.
High-
resistance
loop
Near-end station detects battery reversal and goes on
hook. Line card unit is then ready for the next call.
High-
resistance
loop
Line card unit idle
Line card unit idle
Low-
resistance
loop
Line
card
Near-end
station
Far-end
station
Battery on tip/
ground on ring
Low-
resistance
loop
Battery on tip/
ground on ring
Ground on tip/
battery on ring
Note 1: Battery reversal signalling is a supervisory feature that is only used when the near-end station
originates the call.
553-AAA1115