Class-4 telephone switch

A sector tandem switch connects local telephone exchanges (class-5 switches) and carries traffic within the local access and transport area (LATA).

Before the Bell System divestiture, class-4 switches in a telephone office that had operators present were called "toll centers."

Class-4 switches at that time often had an associated Traffic Service Position System (TSPS) to handle operator-assisted calls.

[4] During the 1980s, class-4 tandem switches were converted to deal only with high-speed digital four-wire circuit connections: T1, T3, OC-3, etc.

The two-wire local line connections to individual telephones were relegated to the class-5 switches.

In the past, most of the accounting, billing management, and call record-keeping was handled by the tandem switches.