A network device, comprising: a physical layer device (110, 120) that is configured for initial communication over a transmission medium in a full duplex mode; and an energy efficiency control policy (118, 128) that is configured to: transition the physical layer device (110, 120) from the full duplex mode to a simplex mode where one of transmission and reception of data on the transmission medium is discontinued; disable cancellation circuitry used by the physical layer device (110, 120) for at least part of the time that the physical layer device (110, 120) operates in the simplex mode; and when both directions of the transmission medium have no data to transmit, enter a low power mode, where both transmission and reception of data on the transmission medium are discontinued, except for short periods of refresh signaling; characterized in that transition from the simplex mode to the low power mode, when there is nothing to transmit or to receive, is precluded by appearance of data on one end of the transmission medium; and transition between the full duplex mode to the simplex mode is conditioned on a waiting period based on a detection whether the one direction of transmission is signaling a transition to the low power mode such that transition to the simplex mode as an intermediate transition to the low power mode is omitted and a direct transition from the full duplex mode to the low power mode occurs. a physical layer device (110, 120) that is configured for initial communication over a transmission medium in a full duplex mode; and an energy efficiency control policy (118, 128) that is configured to: transition the physical layer device (110, 120) from the full duplex mode to a simplex mode where one of transmission and reception of data on the transmission medium is discontinued; disable cancellation circuitry used by the physical layer device (110, 120) for at least part of the time that the physical layer device (110, 120) operates in the simplex mode; and when both directions of the transmission medium have no data to transmit, enter a low power mode, where both transmission and reception of data on the transmission medium are discontinued, except for short periods of refresh signaling; characterized in that transition from the simplex mode to the low power mode, when there is nothing to transmit or to receive, is precluded by appearance of data on one end of the transmission medium; and transition between the full duplex mode to the simplex mode is conditioned on a waiting period based on a detection whether the one direction of transmission is signaling a transition to the low power mode such that transition to the simplex mode as an intermediate transition to the low power mode is omitted and a direct transition from the full duplex mode to the low power mode occurs. transition the physical layer device (110, 120) from the full duplex mode to a simplex mode where one of transmission and reception of data on the transmission medium is discontinued; disable cancellation circuitry used by the physical layer device (110, 120) for at least part of the time that the physical layer device (110, 120) operates in the simplex mode; and when both directions of the transmission medium have no data to transmit, enter a low power mode, where both transmission and reception of data on the transmission medium are discontinued, except for short periods of refresh signaling; characterized in that transition from the simplex mode to the low power mode, when there is nothing to transmit or to receive, is precluded by appearance of data on one end of the transmission medium; and transition between the full duplex mode to the simplex mode is conditioned on a waiting period based on a detection whether the one direction of transmission is signaling a transition to the low power mode such that transition to the simplex mode as an intermediate transition to the low power mode is omitted and a direct transition from the full duplex mode to the low power mode occurs.