Patent ID: 8116212

Claim:
A line status monitoring circuit for a first node which receives a frame through one of a plurality of lines from a second node connected through a redundant transmission channel which is made redundant by the plurality of lines, the line status monitoring circuit comprising: a determining unit which, if a line-specific check frame having an added dedicated header corresponding to each of the plurality of lines is received from the second node through one of the plurality of lines, determines whether or not a further line-specific check frame corresponding to a frame for checking which is identical to a frame for checking included in the received line-specific check frame is received through a predetermined number or more of lines within a predetermined time; and a frame discarding unit which, if the further line-specific check frame is not received through the predetermined number or more of lines within the predetermined time, discards the frame for checking corresponding to the first received line-specific check frame, wherein a connection status of each of a plurality of physical ports corresponding to the plurality of lines is checked, wherein the line-specific check frame is a LAG frame, and wherein the LAG frame is sent to each physical port.