Abstract: An apparatus establishes a common signal channel with a flexible channel capacity for effective utilization of the total traffic capacity between two exchanges or stations which are interconnected by the common signal channel. A traffic detecting unit in one of the exchanges detects a traffic volume in the common signal channel between the exchanges. Based on the detected traffic volume, a channel capacity change determining unit determines whether a channel capacity to which the common signal channel is set needs to be changed or not and determines a new channel capacity to be established for the common signal channel if the channel capacity needs to be changed. If the channel capacity to which the common signal channel is set needs to be changed, a channel capacity change executing unit executes a change in the channel capacity to which the common signal channel is set based on the established new channel capacity.