Nortel Networks Circuit Card ユーザーズマニュアル

 Overview

553-AAA1113

High-

resistance

loop

Line card unit idle

(2-way voice

connection)

Ground on tip/
battery on ring

  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.

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.

Ringing

Low-resistance loop

Near-end station 

off hook

Near-end station goes off hook.

Near-end 

station

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

Alert