Patent ID: 8000232

Claim:
A redundancy controlling method of a transmission device for controlling a first redundancy function that switches between a working line and a protection line in response to a detection of a line error and a second redundancy function that performs a path switching in response to a detection of a path error in a ring network operating at a path rate lower than a line rate thereof, the redundancy controlling method comprising: detecting, by a line error detector of the transmission device, a line error occurring on either the working line or the protection line; enabling, by a switch of the transmission device, the first redundancy function to switch the working line to the protection line in response to the detection of the line error on the working line; detecting, by a path error detector of the transmission device, a path error in a signal output from the switch immediately after a time of the detection of the line error on the working line; and outputting, by a masking unit of the transmission device, a masking signal that masks the path error detection to the path error detector for a period after the time of the detection of the line error and before an expected time of the detection of the path error so that the path switching by the second redundancy function is stopped during the period.