Prior to divestiture , numbers that were assigned to offices according to their hierarchical function in the U.S. public switched telephone network . Note 1: The following class numbers are used:
Class 1: Regional Center (RC)
Class 2: Sectional Center (SC)
Class 3: Primary Center (PC)
Class 4: Toll Center (TC) [Only if operators are present; otherwise Toll Point (TP)]
Class 5: End Office (EO) [Local central office ]
Note 2: Any one center handles traffic from one center to two or more centers lower in the hierarchy. Since divestiture , these designations have become less firm.