Canon fax basic 2000 서비스 매뉴얼
BASIC OF TELEPHONE
1–26
(3) Electronic exchange (D type)
• This has the same function as crossbar’s. Moreover, the electronic
exchange uses a computer as its control unit and provides high reli-
ability.
6.2
The Exchange
An exchange is a device, so it cannot talk or listen like a human being. For
this reason, the telephone sends signals that the exchange can understand,
and the exchange sends signs to the telephone that a human being can
understand.
The Fig. 1-33 shows how an exchange works.
Fig. 1-33 How an Exchange Works
Operation on
calling telephone
calling telephone
Operation on
exchange
exchange
Operation on
called telephone
called telephone
The exchange gets
ready.
ready.
The exchange is
ready to receive
a number.
ready to receive
a number.
After receiving the
signal, the exchange
finds the called
number.
finds the called
number.
The exchange
connects the line.
(Unless the called
number is busy.)
connects the line.
(Unless the called
number is busy.)
Conversation
The exchange stops
ring tone, ring-back
tone and connects
the line.
ring tone, ring-back
tone and connects
the line.
The exchange
disconnects and
halts the DC loop.
disconnects and
halts the DC loop.
DC loop
Dial tone
The handset is off hook.
You hear a dial tone.
Dialing pulse
You dial.
Ring-back tone
You hear ring-back tone.
The handset is on hook.
Ring tone
Telephone rings.
The handset is on hook.
DC loop
The handset is off hook.