Disclosed is a technique for controlling communication between a subject device and an external device. The communication is performed via a second network by an application executed by the subject device connected to a first network different from the second network. In the controlling, occurrence of congestion on a communication line used for the communication is detected by monitoring a state of the communication line. Based on the detecting the occurrence of congestion, a notification is transmitted to the application that has used the communication line on which the occurrence of congestion has been detected. The notification indicates congestion on the communication line in use.