Transmission device and communication system

A transmission apparatus comprising:

• a communication module configured to communicate with a reception device through transmission of data;
• and
• a controller configured to process data that is transmitted in communication between the communication module and the reception device,
• wherein
• the controller is configured to extract data from transmission-scheduled data and produce a transmission-scheduled data list,
• the controller is configured to acquire from the reception device, when data communication between the transmission apparatus and the reception device is interrupted and is then recovered, and an interruption history of the communication is present in the reception device, an unreceived data list indicating data that is not received by the reception device before the communication is interrupted,
• the controller is configured to combine the acquired unreceived data list with the produced transmission-scheduled data list to update the transmission-scheduled data list, and
• the communication module is configured to transmit the updated transmission-scheduled data list to the reception device, and transmit the transmission-scheduled data corresponding to the transmission-scheduled data list to the reception device after transmitting the updated transmission-scheduled data list.