Abstract: A data transmission system includes a server, a network and a plurality of terminals. The server sends data to the terminals via the network and the network connects the server and the plurality of terminals, and the terminal includes a network interface unit that connects to the network and communicates with the other terminals or the server via the network, a storage unit that stores reception data and information on missing of data, a detection unit that detects that the reception data is missing or damaged, and a controller that controls the network interface unit to send a repair request message to the other terminals through multicast when the detection unit detects missing or damaged data of data received from the server, and that controls the network interface unit to send a repair request message to the server when there is not requested data in the other terminals.