An apparatus includes a first port coupled to a first apparatus through a ring line, a second port coupled to a second apparatus through a second line, the second apparatus disposed external to the ring line, the second line configured redundantly with a first line between the first apparatus and the second apparatus, a third port coupled to the first apparatus through a control line for a control signal concerning the first line, and circuitry that detects a fault in the control line, wherein the circuitry detects a fault in the second line, switches the second line from an active line to a standby line in accordance with the detection of the fault in the second line, and while the fault in the control line is detected, shuts down the first port in accordance with the detection of the fault in the second line.