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6. TELEPHONE EXCHANGES
The exchange system and the telephone network have made simultaneous
progress. At first, people used the manual exchange, but now the automatic
exchange has replaced the manual exchange in most offices. In this sec-
tion, let's learn about the types of telephone exchange and how they work.
6.1
Types of Exchanges
The Fig. 1-32 shows the various types of exchange system.
Hardly any manual exchanges are in active use today. So, the following
describes digital exchanges.
(1) Step-by-step (S X S) (A type/H type)
(2) Crossbar type (C type)
Manual
Exchange
system
Automatic
Fig. 1-32 Types of Exchanges
• This mechanically proceeds with operation by dial pulses for each
dialed digit.
• This has many switch contacts and provides a mechanical exchange.
So normal transmission may be disturbed by a lot of noise. This is not
suitable for facsimile use.
• As only dial speed 10PPS telephones can be connected, this is already
an outmoded type of exchange.
• This makes connection only after all digits have been entered.
• This is reliable because it scarcely wears out.
• This has a small amount of switch contacts and provides high quality
for calls.
• This is applicable both dial telephones and pushbutton telephones.
And this type enables many other services to be used.
BASIC OF TELEPHONE
Step-by-step
Common control
1
2
3
4
A type
5
H type
Crossbar type
Electronic
6
exchange
ït
çi
1–25
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