A communication system includes a first device and a second device connected through an electro-optical composite cable. The electro-optical composite cable includes an optical fiber and a power supply cable. The optical fiber is used to transmit a data signal. The power supply cable is used to transmit a direct current. The first device is configured to send a first alternating-current signal to the second device through the power supply cable. The second device is configured to switch a running status based on the first alternating-current signal.