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BASIC OF TELEPHONE
1.3
How do you make a call?
When you call someone, you must take various actions.
Let's consider each individual action needed for making a call.
(1) You pick up the handset. This means you are making a calling request.
(2) The exchange emits the dial tone to indicate it is ready for the called
(3) You dial your party's number. This is the dialing signal.
(4) When the telephone exchange receives your dialing signal, it attempts
(5) When the other party picks up the handset, the exchange stops sending
(6) You have your conversation.
(7) You hang up.
When the called number is in use, the calling party hears a busy tone. Even
if the called party hangs up while the caller is listening, the calling party
will still hear the busy tone. So the calling party needs to dial again.
1.4
Voice Frequencies Carried by the Telephone
The human ear can hear sounds with frequencies between 10 Hz and
15,000 to 20,000 Hz. The human voice is composed of many different fre-
quencies. To be able to transmit the full range of hearing over the phone
line would require very high-quality amplifiers and other equipment. Far
more than is practical.
The telephone transmits enough voice frequencies to understand what is
being said; usually between 300 to 3,400 Hz.
1–4
The telephone
exchange
number.
to connect with your party. If your party is free, the exchange will
make the connection, and you will hear a ringing tone.
the ringing tone, so that you can have a conversation.
gets ready to connect you to your party.
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