A method for configurating a transmission mode to provide an Internet service to a customer-premises equipment by an transmission mode configurating apparatus in an access network structure is provided. At least one network management equipment and at least one customer-premises equipment are connected through a bundle of cables including a plurality of transmission lines. The method includes determining the number of transmission lines connected to the customer-premises equipment; determining at least one of available transmission mode to provide depending on the number of transmission lines; if a plurality of available transmission modes are determined, calculating a transmission performance in each of the available transmission modes; and selecting the transmission mode with the highest performance among the plurality of the available transmission modes.