class 4 switch

In the USA, the large telephone switches in the switching technology in wide area networks are classified hierarchically.

The Class-4 switch is a switching node for trunk connections in wide area switching. Class-4 switches form a switching function for toll traffic that they receive from Class-5 switches and transmit through the trunks to other Class-4 switches. A Class 4 node can also operate as a Class 5 switch.