of 400 lines or less. A 100-amp unit is required for
electromechanical switches. These switches are called
systems of 500 lines or greater.
The crossbar switches are able to switch 10 three-
Digital logic and integrated circuit technology is
wire inputs to any of 30 three-wire outputs, or con-
used to interrupt, decode, determine path availability,
versely 30 inputs to 10 outputs by using these switches
and identify and notify a switch to operate. But,
in a series and parallel combination, the 1 to 999 capa-
the actual voice circuit is completed through
bility (in the 500-line system) is achieved.
Figure 6-49.--Dial telephone central office section, cutaway.