Abstract: Arrangements dealing with multiple link failures occurring in a communication network including a first ring and a second ring connected to the first ring by sharing part of a link in the first ring as a common link. Included is stored link failure information included in the failure detection frame, and where a controller configured to control the communication unit to stop transmission of at least one auxiliary monitor frame in the event of multiple failures including a failure on the common link, but to allow transmission under certain specific circumstances.

Abstract: In a communication network including a monitor device, a relay device, and a common link terminal device, in response to detection of a link failure in a ring, each device sends a failure detection frame to the ring and causes link failure information to reach the common link terminal device. The common link terminal device generates a link failure information management database, performs a multi-failure detection process, and stops transmission of an auxiliary monitor frame upon detection of multiple failures.