A communication network system includes a communication line, a plurality of communication stations each having a node coupled to the communication line and a network controller coupled to the stations for controlling routing for communication messages between nodes. In one embodiment, the messages are sent from plural terminals connected with each node along with communication performance prerequisites. The communication performance prerequisites for a communication message are discriminated in the node which receives the message. Traffic in various routes between the nodes is continually measured in the communication stations and the measuring results are stored in a database storage unit. Future traffic in the various routes is predicted on the basis of the information on the continually measured traffic by the use of a predetermined algorithm and stored in the storage unit for use in determination of routes for communication messages on the basis of the result of the communication performance prerequisites discrimination and predetermined criteria with respect to the updated information on the predicted traffic in the storage unit.