A switching trunk that connects, i.e., that switches, one or more end offices to a toll office as the first stage of concentration of long-distance calls. Note: Operator or attendant assistance or participation may be an optional function. In U.S. common-carrier telephone service, a toll office once designated as “Class 4C” is an office where assistance in completing incoming calls is provided in addition to other traffic. A toll office once designated as “Class 4P” is an office where (a) operators handle only outbound calls or (b) switching is performed without human intervention. See also  attendant position,  call,  concentrator,  connection,  end office,  long-distance call,  operator,  stage,  switching,  switching system,  toll office,  traffic,  trunk.