Canon fax basic 2000 Manuale Di Servizio

A–21

çi

6. POLARITY INVERSION ON

EXCHANGE

The Fig. A-16 shows the standard operation of an exchange in order to

explain polarity inversion. This example is for an exchange operating in

Japan. The polarity on the calling side is reversed simultaneously with the

called party becoming offhook. The original polarity is restored simulta-

neously with the end of the telephone conversation and the called party

becoming onhook.

On some facsimiles, the characteristics of the telephone line are used when

to perform auto-dialing.

Polarity is not reversed on some exchanges overseas and some private

branch exchanges.

Fig. A-16 Example of Standard Operation of Exchange in Japan

Selects the called party,
inverts the polarity and
sends the calling
identification.
Sends the ringing back tone
to the calling party.

Restores original polarity
after response from called
party.
Deactivates the calling
identification.
Inverts the polarity on the
calling party and
deactivates the ringing
back tone.

Telephone State

Operation of Exchange

Telephone Line State

Both
onhook
(normal state)

Monitors states of
terminals.

Calling party
offhook
(loop closed)

Exchange is started up.
Dial tone is sent to calling
party.

Calling party

Exchange

Called Party

+ Earth

Long high-

pitched sound

Dial tone

Transmission of
dialing signal

Operation of exchange
Selects the called party.

Dialing signal

+ Earth

Calling called
party in progress

Ringing back

tone

+ Earth

Ringing back tone

Calling identification

+ Earth

Called party
offhook
(loop closed)

Voice transmission

End of call
Both onhook

Restores all lines to their
original states.

+ Earth

– 48V