Hi Obiviate,
these values, as you know are wavelength dependent. OptiSystem use the default values of these parameters at 1550 nm operating wavelength.
Such as, attenuation is 0.2 dB/km
Dispersion (D) is 16.75 ps/nm/km
Dispersion (Beta 2) is -20 ps^2/km
other parameters of nonlinearity like cross section area, refractive index ….are also used
hope this helps,
thanks
Mohamed Abouseif