A network device, comprising: a physical layer device that is configured for initial communication over a transmission medium in a full duplex mode ; and an energy efficiency control policy that is configured to: transition the physical layer device 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 for at least part of the time that the physical layer device 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 that is configured for initial communication over a transmission medium in a full duplex mode ; and an energy efficiency control policy that is configured to: transition the physical layer device 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 for at least part of the time that the physical layer device 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 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 for at least part of the time that the physical layer device 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. <EOS>