The Evolution Of Switches - AT&T MERLIN LEGEND Release 3.1 System Manager's Manual

Background
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.
Telephone
Station
Party-Line
Private-Line
Service
Service
Telephone
Station
Switch
Central Office
Station Switching
Centralized Switching
Figure 2–3. The Evolution of Switches
2–7
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