Nortel Networks 553-3001-211 manual Far-end Station System Line card Near-end

Page 46 of 894 Overview

Figure 9

Hook flash disconnect supervision sequence

Far-end

station

System

Line card

Near-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

Signal/direction

	High-
Ground on tip/	resistance
battery on ring	loop

Ringing

Low-resistance loop

	Low-
Ground on tip/	resistance
battery on ring	loop
	Low-
Tip open/	resistance
battery on ring	loop
	High-
Tip open/	resistance
battery on ring	loop
	High-
Ground on tip/	resistance
battery on ring	loop

Remarks

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.

The system detects increase in loop current, trips ringing, and cuts call through to near-end station.

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 flash (tip removed from ground) to the near-end station.

The near-end station responds by going on hook, presenting a high-resistance loop to the system.

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)

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-AAA1116

553-3001-211 Standard 2.00 September 2004