Nortel Circuit Card Installation Manual page 47

Figure 8
Battery reversal answer and disconnect supervision sequence
System
Far-end
station
State
Line card unit idle
Call request
Outpulsing
(2-way voice
connection)
Near-end station
on hook
Line card unit idle
Far-end station
on hook
Line card unit idle
Note 1: Battery reversal signalling is a supervisory feature that is only used when the near-end station
originates the call.
Line
card
Near-end
Signal/direction
High-
resistance
Ground on tip/
loop
battery on ring
Low-resistance loop
Dial tone
Addressing signals
Dial tone removed
Ringback (or busy)
Low-
resistance
Battery on tip/
loop
ground on ring
High-
Battery on tip/
resistance
ground on ring
loop
High-
Ground on tip/ resistance
loop
battery on ring
Low-
Ground on tip/ resistance
battery on ring loop
High-
Ground on tip/ resistance
battery on ring loop
station
Remarks
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.
Dial tone is applied to the near-end station from the
system.
Near-end station dials number (loop pulsing or DTMF
tones).
The system detects start of dialing and removes dial tone.
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.
If near-end station hangs up first, a high-resistance loop is
presented to the system.
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.
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.
Near-end station detects battery reversal and goes on
hook. Line card unit is then ready for the next call.
Circuit Card
Overview Page 47 of 906
553-AAA1115
Description and Installation