Nortel Circuit Card Installation Manual page 48

Page 48 of 906 Overview
Figure 9
Hook flash disconnect supervision sequence
Far-end
station
State
Line card unit idle
Call request
Alert
Near-end station
off hook
(2-way voice
connection)
Far-end station
on hook
Near-end
station on hook
Line card unit idle
Note 1: Hook-flash signalling is a supervisory feature that is only used when the far-end station
originates and terminates the call. If the far-end station originates the call but the near-end
hangs up first, a hook flash is not sent.
Note 2: If the end of the hook-flash interval occurs before the near-end station goes on hook, the
system waits until the near-end station does so before placing the line card unit in the
idle state.
553-3001-211 Standard 3.00
Line
System card
Signal/direction
resistance
Ground on tip/
battery on ring
Ringing
Low-resistance loop
resistance
Ground on tip/
battery on ring
resistance
Tip open/
battery on ring
resistance
Tip open/
battery on ring
resistance
Ground on tip/
battery on ring
August 2005
Near-end
station
Remarks
High-
loop
No battery current drawn.
Far-end station goes off hook and addresses
(dials up) near-end station. The system
receives the incoming call and determines that
the call is for a specific unit terminal number
(TN) and assigns message timeslots.
The system applies 20 Hz ringing to the ring
lead.
Near-end station goes off hook.
Low-
loop
The system detects increase in loop current,
trips ringing, and cuts call through to near-end
station.
Low-
loop
When the far-end station hangs up, the
following happens: The system detects
disconnect signalling from the far end, removes
the timeslot assignments, and sends a hook
High-
flash (tip removed from ground) to the near-end
station.
loop
The near-end station responds by going on
High-
hook, presenting a high-resistance loop to the
system.
loop
At the end of the hook-flash interval, the
system returns the tip to ground. The line
card unit is then ready for the next call. (Note 2)
553-AAA1116