Class 4 Telephone Switch
A Class 4, or Tandem, telephone switch is a U.S. telephone company central office telephone exchange used to interconnect local exchange carrier offices for long distance communications in the Public Switched Telephone Network.
A Class 4 switch doesn't connect directly to any telephones; instead, it connects to other Class 4 switches and to Class 5 telephone switches. The telephones of people who subscribe to telephone service are wired to Class 5 switches. When a call is placed to a telephone that isn't on the same Class 5 switch as the subscriber, the call may be routed through one or more Class 4 switches to reach its destination.
Read more about Class 4 Telephone Switch: Taxonomy, History, Switching Equipment
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