  We consider the evolution of a parton system which is formed in the central
region just after a relativistic heavy ion collision. The parton consist of
mostly gluons, minijets, which are produced by elastic scattering between
constituent partons of the colliding nuclei. We assume the system can be
described by a semi-classical Boltzmann transport equation, which we solve by
means of the test particle Monte-Carlo method including retardation. The
partons proliferate via secondary radiative $gg \to ggg$ processes until the
thermalization is reached for some assumptions. The extended system is
thermalized at about $t=1.6$ fm/$c$ with $T = 570$ MeV and stays in equilibrium
for about 2 fm/$c$ with breaking temperature $T = 360$ MeV in the rapidity
central region.
