The present invention discloses a data transmission method for transmitting real-time data from a server to plural terminals via a network having plural local area networks connected to a wide area network. The method includes the steps of grouping plural terminals connected to a same switching hub into a single terminal group, generating a table indicating a rank and an address of each terminal in the terminal group, and transferring the real-time data from a first terminal to a second terminal that is one rank lower than the first terminal in accordance with the ranks indicated in the table.