  There have been a long string of efforts to understand the source of the
variability observed in microquasars but no model has yet gained wide
acceptance, especially concerning the elusive High-Frequency Quasi-Periodic
Oscillation (HFQPO). We first list the constraints arising from observations
and how that translates for an HFQPO model. Then we present how a model based
on having the Rossby Wave Instability (RWI) active in the disk could answer
those constraints.
