Optical transmission system, node apparatus, and reachability determination method

An optical transmission system comprising:

• a plurality of node apparatuses installed at nodes located on a first route from a start node to an end node, wherein each of the node apparatuses includes:
• a receiver configured to receive, from an adjacent node, routing information specifying the first route and a first parameter representing a cumulative amount of signal degradation that is cumulative from the start node to the adjacent node;
• a parameter calculating unit configured to
• update the first parameter by adding, to the first parameter, a second parameter representing an amount of signal degradation along a pathe to the adjacent node, and
• generate, using the updated first parameter, a third parameter representing the cumulative amount of signal degradation along a transmission route between the start node and the first node, the start node being specified by the routing information;
• a determination unit configured to determine reachability of the first route by adding the third parameter and a fourth parameter representing an amount of signal degradation along a transmission route from the first node to the end node to obtain an added amount and determine if the added amount is lower than a permissible amount of degradation at the first node;
• and
• a transmitter configured to transmit the routing information and the third parameter to an adjacent node toward the end node.