  We revisit the phenomenon of the resonant transmission of fermionic carriers
through a quantum device connected to two contacts with different chemical
potentials. We show that, besides the traditional in solid-state physics
Landauer-B\"uttiker approach, this phenomenon can be also described by the
non-Markovian master equation for the reduced density matrix of the fermions in
the quantum device. We identify validity regions of both approaches in the
system parameter space and argue that for large relaxation rates the accuracy
of the latter approach greatly exceeds the accuracy of the former.
