Office classification
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Office classification: Prior to divestiture, numbers that were assigned to offices according to their hierarchical function in the U.S. public switched telephone network.
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 ].
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.