Delivery device, communication system, load balancing method, and load balancing program

A communication system, comprising:

• a delivery device;
• and
• a plurality of terminals that are communicable with the delivery device,
• wherein each of the terminals includes a connection maintenance control unit that communicates to the delivery device connection maintenance signal interval information to specify intervals between connection maintenance signals to maintain connections between the delivery device and the terminals, and
• the delivery device includes:
• a communication unit that, when there is no data to be delivered, transmits connection maintenance signals to the respective terminals;
• and
• a transmission time determination unit that divides into a plurality of time slots a period in which the communication unit transmits the connection maintenance signals, calculates the number of expected transmissions of connection maintenance signals with respect to each time slot on the basis of the connection maintenance signal interval information received from the respective terminals, and, when the number of expected transmissions exceeds a predetermined threshold value, makes the communication unit transmit, in a time slot that is earlier than the time slot, a connection maintenance signal corresponding to the number of expected transmissions exceeding the threshold value.

A load balancing method which is carried out by a delivery device that, when there is no data to be delivered, transmits, to respective terminals connected to the delivery device, connection maintenance signals to maintain connections between the delivery device and the respective terminals, the method comprising the steps of:

• dividing into a plurality of time slots a period in which the delivery device transmits the connection maintenance signals;
• calculating the number of expected transmissions of connection maintenance signals with respect to each time slot on the basis of connection maintenance signal interval information indicating intervals between connection maintenance signals to the respective terminals;
• and
• when the number of expected transmissions exceeds a predetermined threshold value, transmitting a connection maintenance signal corresponding to the number of expected transmissions exceeding the threshold value in a time slot that is earlier than the time slot.