Instruction manual

Background
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Party-Line Service. Several telephones were connected to one line so
that a number of people could communicate in the same conversation.
But there was no way to reach a telephone on any other line.
■
Station Switching. All telephones were connected to all other
telephones. The telephone itself performed the switching and made the
connection. This was workable for a small number of telephones, but
quickly became impractical as hundreds of telephones were installed.
■
Centralized Switching. As the number of telephones grew, all the lines
from all the telephones came to a common
central office (CO) or
exchange , so that the lines could be electrically cross-connected.
Human operators made the connections.
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Private-Line
Service
Telephone
Station
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Party-Line
Service
Station Switching
Telephone
Station
Switch
Central Office
Centralized Switching
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Figure 2–3. The Evolution of Switches
About the System
2–
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