which implies that advection should be significant at least close to the horizon. The very first model of accretion onto black holes was of course radial inflow of matter, which was basically the general relativistic version of the Bondi solutions [@b52; @m72]. However, the infall time scale of radial accretion onto black holes is short, and therefore has very little time to produce the huge luminosities observed from AGNs and microquasars [@s73]. On the other hand, @ss73 considered a geometrically thin but optically thick accretion disc characterized by negligible advection, but by virtue of possessing Keplerian angular momentum distribution, the disc was rotation dominated. This disc model was radiatively efficient and produced the multi-coloured blackbody part of the spectra or the ‘blue bump’ radiated by the AGNs. However, the presence of hard power-law tail in the spectra of the black hole candidates indicated the necessity of a hot Comptonizing cloud, which was neither present in Keplerian disc nor its origin could be identified in any self-consistent manner from such a disc. Therefore, models with advection gained importance. Theoretically, it was shown that in a significant range of energy and angular momentum, multiple sonic points may exist for rotating, transonic accretion 