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

 Overview

553-AAA1114

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.

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.

Low-resistance loop

Dial tone is applied to the near-end station from 
the system.

Call request

Dial tone

Addressing signals

Outpulsing

Near-end station dials number (loop pulsing or 
DTMF tones).

Near-end 

station

Dial tone

The system detects start of dialing and 
removes dial tone.

Ringback (or busy)

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.

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