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553-3001-211 Standard 2.00 September 2004
Figure 7
Call connection sequence – near-end originating call
553-AAA1114
High-
resistance
loop
Line card unit idle
(2-way voice
connection)
Remarks
Ground on tip/
battery on ring
Signal/directionState
System
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, the following
occurs: Line card detects drop in loop current.
CPU removes timeslot assignments.
If far-end station hangs up first, the following
occurs: The system detects disconnect signaling
from trunk. CPU removes timeslot assignments.
Person at near-end station recognizes end of
call and hangs up.
No battery current drawn.
Near-end station goes off hook. Battery current
is drawn causing detection of off-hook state.
CPU 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).
Near-end
station
Dial tone
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, ringback tone is
removed , and call is cut through to far-end
station.
Line card unit is ready for the next call.
High-
resistance
loop
Line card unit is ready for the next call.
High-
resistance
loop
Line card unit idle
Line card unit idle
High-resistance loop
Far-end
station
through
PSTN