  We perform a comparative spectro-temporal analysis on the variability classes
of GRS 1915+105 and IGR J17091-3624 to draw inferences regarding the underlying
accretion flow mechanism. The $\nu$, as well as C2 class Rossi X-Ray Timing
Explorer observation, have been considered for analysis. We investigate the
intensity variation of the source in different energy domains that correspond
to different components of the accretion flow and infer the relative dominance
of these flow components during the dip/flare events. We correlate the
dependence of the dynamic photon index ($\Theta$) with intensities in different
energy bands and comment on the transition of the source to hard/soft phases
during soft dips/flares. We also report the presence of sharp QPOs at \sim7.1
Hz corresponding to both softer and harder domain in the case of $\nu$
variability class of GRS 1915+105 and discuss the possible accretion flow
configuration it suggests. Sharp QPO around \sim20 mHz is observed in $\nu$ and
C2 classes of IGR J17091-3624 in low and mid energy band (2.0-6.0 keV and
6.0-15.0 keV), but remains undetected in high energy (15.0-60.0 keV). The
2.5-25.0 keV background-subtracted spectra have also been fitted with TCAF
along with a Compton reflection component. A plausible accretion flow mechanism
in order to explain the observed variability has been proposed.
