office classification
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.