COMMUNICATION NETWORK SYSTEM AND TROUBLE DETECTING APPARATUS

摘要

A communication network system capable of quickly detecting any trouble that occurs in a Layer 2 network having a ring-shaped network topology. In a communication network system of an open ring shape, virtual LANs (1-3,11-13) connecting a master node (20A) and slave nodes (30A-30C) are established in two different communication path directions along the ring for each set of the master node (20A) and a respective one of the slave nodes (30A-30C), and the ports at the link ends of the master node (20A) and slave node (30C) are blocked. The master node (20A) and slave nodes (30A-30C) each have two communication ports for transmitting and receiving information via adjacent links and a trouble detection part for detecting any communication troubles, and causes one of the communication ports that is different from the other one receiving a communication trouble to transmit/forward communication trouble information.