Abstract: IP over DWDM （Dense Wavelength Division Multiplexing）optical Internet is one of the mainstream networ king techniques for NGI （Next Generation Intemet）backbone, and how to improve its fault-tolerance capability and QoS provision becomes critical. Fault-to

Key words: NGI, IP/DWDM optical Internet, QoS unicast routing, Preventive fault-tolerance, Ant colony algorithm, Genetic algorithm