A telephone switching center (central office) that does not connect directly to the customer. It connects offices in the same network or between networks, but always deals with trunks rather than customer lines. After Divestiture, most Class 4 tandem offices moved to AT&T, while Class 5 local tandem offices stayed with the RBOCs.RBOCs installed new tandem offices to handle intraLATA toll calls and provide access to the interLATA toll carriers. Tandem offices and end offices are generally located in the same facility, and may even be serviced by the same switch. See LATA, tandem switch and end office switch.