Embodiments of the present invention disclose an add/drop multiplexer, including a first line board and a tributary board, where the first line board includes at least a first interface and a second interface, the first interface is disposed between the tributary board and the first line board, and the second interface is disposed on a network side of the first line board; the first line board is configured to receive a first signal from a first link, and output the first signal through the second interface; the first line board is further configured to receive a second signal from the first link, and output the second signal to the tributary board through the first interface; and the first line board is further configured to receive a third signal from the tributary board through the first interface, and input the third signal into the first link. By using the foregoing technical solutions, an inter-board interface on a link is effectively eliminated, thereby reducing complexity, power consumption, and costs
