  We have studied the quantum oscillations in the conductivity of metallic,
p-type Bi$_2$Se$_{2.1}$Te$_{0.9}$. The dependence of the oscillations on the
angle of the magnetic field with the surface as well as the Berry phase
determined from the Landau level fan plot indicate that the observed
oscillations arise from surface carriers with the characteristic Dirac
dispersion. Several quantities characterizing the surface conduction are
calculated employing the Lifshitz-Kosevich theory. The low value of the Fermi
energy with respect to the Dirac point is consistent with the metallic
character of the bulk hole carriers. We conclude that, due to the peculiar
shape of the valence band, the Shubnikov-de Haas oscillations of the bulk
carriers are shifted to higher magnetic fields which allows for the detection
of the quantum oscillations from the topological surface states at lower field.
