We identify the key role played by the network topological parameters in the optimisation of the wavelength-routed optical network design by considering existing or planned network topologies and link failure restoration. We analyse the network topological parameters for the optimisation of the wavelength routed optical network (WRON) design and show that average internodal distance H, diameter D and connectivity /spl alpha/ play a major role on the network wavelengths requirement. The number of links in the limiting cut determines the maximum number of extra wavelength required in case of a link failure. The results also help to explain why wavelength translation does not significantly reduce the network wavelength requirements.