Patent ID: 7768915

Claim:
A main apparatus which connects to an internet protocol (IP) network including a plurality of lines to connect a plurality of telephone terminals, and executes communication connection between the plurality of telephone terminals, the plurality of telephone terminals include at least a first and a second telephone terminal, at least the first and the second telephone terminals are included in a group sharing at least one of the plurality of lines, the apparatus comprising: a transmitter updates an available/busy state of the one of the plurality of lines, and transmits a control signal notifying a communication connection to the first telephone terminal included in the group and the second telephone terminal included in the group, when the first telephone terminal establishes the communication connection by using the one of the plurality of lines; a monitoring module configured to monitor congestion of at least the main apparatus; and a controller which controls execution and stoppage of transmission processing of the control signal to the second telephone terminal carried out by the transmitter based on a result of congestion monitoring carried out by the monitoring module.