Nortel Circuit Card Installation Manual page 43

Figure 6
Call connection sequence – near-end station receiving call
Far-end
station
through
PSTN
State
Line card unit idle
Alert
Near-end station
off hook
(2-way voice
connection)
Near-end station
on hook
Line card unit idle
Far-end station
on hook
Line card unit idle
System
Signal/direction
Ground on tip/
battery on ring
Ringing
Low-resistance loop
High-resistance loop
Ground on tip/
battery on ring
High-resistance loop
Ground on tip/
battery on ring
Near-end
station
High-
resistance
loop
No battery current drawn.
Far-end station goes off hook and
addresses (dials up) near-end station.
The system receives the incoming
call on a trunk and determines that the
call is for a specific unit terminal number
(TN) and assigns message timeslots.
The system applies 20 Hz ringing to
ring lead.
Near-end station goes off hook.
The system detects increase in loop
current, trips ringing, and cuts call
through to near-end station.
If near-end station hangs up first, the
following occurs: Line card detects drop
High-
resistance in loop current. CPU removes timeslot
loop assignments.
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. Person
High-
at near-end station recognizes end of
resistance
call and hangs up.
loop
Line card unit is ready for the next call.
Circuit Card
Overview Page 43 of 906
Remarks
553-AAA1113
Description and Installation