Thermalization of a longitudinally expanding color glass condensate withBjorken boost invariant geometry is investigated within microscopical partoncascade BAMPS. Our main focus lies on the detailed comparison ofthermalization, observed in BAMPS with that suggested in the \BUp scenario. Wedemonstrate that the tremendous production of soft gluons via $gg \to ggg$,which is shown in the \BUp picture as the dominant process during the earlypreequilibration, will not occur in heavy ion collisions at RHIC and LHCenergies, because the back reaction $ggg\to gg$ hinders the absolute particlemultiplication. Moreover, different from the \BUp scenario, soft and hardgluons thermalize at the same time. The time scale of thermal equilibrationobtained from BAMPS calculations is of order $\as^{-2} (\ln \as)^{-2}Q_s^{-1}$. After this time the gluon system exhibits nearly hydrodynamicalbehavior. The shear viscosity to entropy density ratio has weak dependence on$Q_s$ and lies close to the lower bound from the AdS/CFT conjecture.
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