Nortel NT1R20 Description page 62

Page 38 of 290 Description
Figure 14
Battery reversal answer and disconnect supervision sequence
Meridian 1
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.
553-3001-105 Standard 5.00 June 1999
Line
card
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/
ground on ring loop
High-
Battery on tip/
resistance
ground on ring
loop
High-
Ground on tip/ resistance
battery on ring loop
Low-
Ground on tip/ resistance
battery on ring loop
High-
Ground on tip/ resistance
battery on ring loop
Near-end
station
Remarks
No battery current drawn.
Near-end station goes off hook. Battery current is drawn
causing detection of off-hook state. Meridian 1
determines unit terminal number (TN) and assigns
message timeslots.
Dial tone is applied to the near-end station from the
Meridian 1.
Near-end station dials number (loop pulsing or DTMF
tones).
Meridian 1 detects start of dialing and removes dial tone.
Meridian 1 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 Meridian 1.
Meridian 1 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 Meridian 1 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.
553-7517