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BASIC OF TELEPHONE
As the transit exchange relay-switches conversations between subscriber
exchange, we can consider transit exchange to be ranked (classified)
higher than the subscriber exchange. The rank for an exchange is called the
grade, and the telephone center is called the center grade. That is, the high
grade exchanges can route calls to a wider area.
5.3
Nationwide Telephone Network (In case of Japan)
The nationwide network in Japan can be divided into subscriber areas
matched with administrative districts. A subscriber area has more than one
subscriber exchange to connect all the telephones in the area.
A call within the area is called a local call, and can be made by dialing an
exchange number and the subscriber number.
1–20
Fig. 1-23 Center Grade
Exchange
Local call
Subscriber area
Fig. 1-24 Subscriber Area and Local Call
Transit exchange
Subscriber exchange
Telephone
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