The Exchange - Canon FACSIMILE BASIC 2000 Service Manual

BASIC OF TELEPHONE
(3) Electronic exchange (D type)
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.
1–26
• This has the same function as crossbar's. Moreover, the electronic
exchange uses a computer as its control unit and provides high reli-
ability.
Operation on
calling telephone
DC loop
The handset is off hook.
Dial tone
You hear a dial tone.
Dialing pulse
You dial.
Ring-back tone
You hear ring-back tone.
The handset is on hook.
Fig. 1-33 How an Exchange Works
Operation on
Operation on
exchange called telephone
The exchange gets
ready.
The exchange is
ready to receive
a number.
After receiving the
signal, the exchange
finds the called
number.

The exchange

Ring tone
connects the line.
(Unless the called
number is busy.)
The exchange stops
DC loop
ring tone, ring-back
tone and connects
the line.
Conversation
The exchange
disconnects and
halts the DC loop.
Telephone rings.
The handset is off hook.
The handset is on hook.