COMMUNICATION SYSTEM

PROBLEM TO BE SOLVED: To solve a problem caused in an untransmissible traffic without having node map faults by including plural interconnected nodes and allowing the nodes to check an instruction from a source and to identify the untransmissible traffic. SOLUTION: Normal traffic carried by a work channel in one fiber is protected by a protection channel traveling in the opposite direction around a ring. This allows two-way transfer of the normal traffic. Only one set of overhead channels is used for each fiber. Each fiber carries protection traffic together with the normal (work) traffic in a two-fiber span, and each fiber carries two pieces of traffic in opposite directions. The traffic includes a control byte indicating a traffic source, the system includes plural interconnected nodes, and the nodes identify untransmissible traffic by checking an instruction of the source.