Nortel Circuit Card Installation Manual page 44

Page 44 of 906 Overview
Figure 7
Call connection sequence – near-end originating call
Far-end
station
through
PSTN
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
553-3001-211 Standard 3.00
System
Signal/direction
resistance
Ground on tip/
battery on ring
Low-resistance loop
Dial tone
Addressing signals
Dial tone
Ringback (or busy)
High-resistance loop
Ground on tip/ resistance
battery on ring
High-resistance loop
Ground on tip/ resistance
battery on ring
August 2005
Near-end
station
Remarks
High-
loop
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.
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, ringback tone is
removed , and call is cut through to far-end
station.
If near-end station hangs up first, the following
High-
occurs: Line card detects drop in loop current.
CPU removes timeslot assignments.
loop
Line card unit is ready for the next call.
If far-end station hangs up first, the following
occurs: The system detects disconnect signaling
from trunk. CPU removes timeslot assignments.
High-
Person at near-end station recognizes end of
call and hangs up.
loop
Line card unit is ready for the next call.
553-AAA1114