Class-4 telephone switch

（重定向自Tandem office）

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 service subscribers are wired to class-5 switches. When a call is placed to a telephone that is not 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.

单词	Tandem office
释义	Tandem office 英语百科 Class-4 telephone switch （重定向自Tandem office） 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 service subscribers are wired to class-5 switches. When a call is placed to a telephone that is not 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.
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