USB extension devices that transmit USB 3.0 differential signaling over an extension medium that supports serial communication are provided. In some embodiments, an electrical idle or suspend is detected from a transmit conductor of a USB host or device, and a corresponding USB extension device is reconfigured to couple a receive conductor of the USB host or device to a null data source instead of an extension medium transceiver. Once the electrical idle or suspend state ceases, the receive conductor of the USB host or device is reconnected to the extension medium transceiver. In some embodiments, a transmit input of the extension medium transceiver is coupled to a null data source upon detection of electrical idle or suspend from the USB host or device.