national switching equipment congestion signal

In international communications, a signal that (a) is sent in the backward direction and (b) indicates that the call setup attempt was unsuccessful because of the congestion encountered at a switching center in a national network, i.e., that the access attempt ended in access failure. See also access, access attempt, access failure, backward direction, call setup, congestion, electronic signal, forward direction, network, optical signal, signal, switching center, switching equipment.