Patent ID: 8255575

Claim:
A monitoring apparatus which constitutes a portion of a ring network of ring topology and which monitors said ring network, said monitoring apparatus comprising: a first ring port and a second ring port, which constitute connections to said ring network, where said first ring port and said second ring port are different ports from one another; wherein said monitoring apparatus periodically transmits health check frames for monitoring a ring status of said ring network from said first ring port and said second ring port to the ring network; and said monitoring apparatus monitors said ring status, depending upon such conditions as to whether or not said health check frame transmitted from said first ring port in a first-loop-direction to travel around the ring network has been received back by said second ring port, and whether or not said health check frame transmitted from said second ring port in a second-loop-direction opposing to said first-loop-direction to travel around the ring network has been received back by said first ring port; responsive to reception of said health check frame by any one, or both ring ports of said first ring port and said second ring port, said monitoring apparatus judges that said ring status is under normal condition, and sets any one of said first and second ring ports into a condition to not transmit/receive a user frame; in failure to reception of said health check frames by both said first and second ring ports, the monitoring apparatus judges that said ring status is under abnormal condition, and sets said ring port which has been brought into said condition to not transmit/receive a user frame, into another condition to transmit/receive said user frame; and said monitoring apparatus determines said ring ports for controlling whether or not the transmission/reception of said user frame are permitted based upon port numbers of said first and second ring ports, or determines said ring ports by receiving a designation issued from a user.