In a communication system in which a server apparatus on the Internet is connected to at least one client apparatus on an intranet via a firewall, the client apparatus comprises: acquisition means for acquiring, from the server apparatus, information associated with a transmission interval at which notifications are periodically transmitted to maintain the connection to the server; and management means for maintaining the connection by periodically transmitting the notifications based on the information associated with the acquired transmission interval, and the server apparatus comprises: decision means for deciding an interval, in which the connection in the push communication can be maintained in non-communication, based on the communication status information; and notification means for notifying the client apparatus of the decided interval as information associated with the transmission interval used to maintain the connection in the push communication.