Abstract: After establishing a connection between an ATU-C and an ATU-R and having a state where data communication is enabled, the ATU-R checks a packet that flows through a network at the user side. When there is no packet addressed to the ATU-R for a predetermined time period, the ATU-R transmits, to the ATU-C, a request to transition to an energy-save mode. The ATU-C and AUT-R determines a parameter to be used for the energy save mode, the parameter enabling a number of carriers and/or transmission power to be decreased compared to the ones in a normal mode. Using the determined parameter, a state in which data communication is enabled is maintained.

Abstract: In an ATU-R having established a connection with an ATU-C and being in a state where data communication is enabled, the ATU-R being located at a user's home, a voltage detection circuit detects a connector voltage of a connector to which a network cable of a user side is connected. When the connector voltage is decreased below a predetermined value in a state where power is supplied to an ADSL circuit of the ATU-R, the power supply to the ADSL circuit is stopped while maintaining a function related to detecting the connector voltage and controlling the power supply. The connector voltage is monitored even after the power supply is stopped. When the detected connector voltage becomes greater than the predetermined value, the power supply to the ADSL circuit is resumed.