Path control apparatus, path control method, path control program, and network system

A path control method for a path control apparatus, comprising the steps of:

• detecting a status change of a network;
• deciding a path in accordance with the status of the network;
• and
• comparing a shortest path tree, which is established before occurrence of a change in the status of the network calculated in the step of deciding a path, with a shortest path tree, which is established after the occurrence of the change in the status of the network, and creating information required for determining whether a node apparatus in the network needs a path update, when the change occurs in the status of the network.

A network system comprising:

• a status change detecting unit that detects a status change of a network;
• a path calculating unit that decides a path in accordance with the status of the network;
• and
• a calculation execution node deciding unit that compares a shortest path tree, which is established before occurrence of a change in the status of the network calculated by the path calculating unit, with a shortest path tree, which is established after the occurrence of the change in the status of the network calculated by the path calculating unit, and creates information required for determining whether a node apparatus in the network needs a path update, when the change occurs in the status of the network.