PURPOSE: To prevent the deterioration in the service and to reduce the communication cost by providing a means selecting a time slot based on the estimate result for a communication time, a means sending a message based on the estimate result of the communication time and a means making redialing.

CONSTITUTION: The system is provided with a revision time storage device 3 storing a time when a line capacity changes, a time slot attribute storage device 4 storing whether the operating state of the time slot and the time slot itself are fixed or tentative, and a communication time estimate device 5 to estimate the communication time based on the revision time storage device 3 and the attribute storage device 4, a time slot designation means 6 to allocate a time slot based on the revision time storage device 3 and the attribute storage device 4, a message transmitter 7 to send a message to a terminal equipment based on the result of the communication time estimate device 6 and a redialing command means device 8 to send again a data when the estimate has an error and the data is interrupted on its way. Thus, the network is operated efficiently.