The transition process in a supersonic at-plate boundary layer at Mach 2 is inves- tigated numerically using linear stability theory (LST) and direct numerical simulations (DNS). Experimental investigations by Kosinov et al. serve as a reference and provide the physical conditions for the numerical setup. In these experiments, the weakly nonlinear regime of transition was studied resulting in the discovery of asymmetric subharmonic resonance triads composed of one primary oblique wave of frequency 20 kHz and two oblique subharmonic waves of frequency 10 kHz. The experimentalists concluded that during the transition process, specific subharmonic resonance triads are selected depending on the am- plitude ratio between fundamental and subharmonic disturbances. With the simulations presented in this paper, the subharmonic transition route is studied in detail. A similar subharmonic resonance mechanism as observed in the experiments is also visible in our numerical simulations. Additionally, several other resonance triads can be identified using LST and DNS. In our simulations, the selection process for a specific triad is not influenced by the amplitude ratio of fundamental and subharmonic disturbances. In contrast to the experiments, the DNS results show that the phase relation between disturbances of both frequency plays a more crucial role.