  A transport model for ultra-relativistic nucleus-nucleus collisions based on
the mean free path approach is proposed. The method is manifestly Lorentz
invariant. We discuss some calculations for pp and AA collisions and compare to
a previously proposed transport model and to data. We demonstrate that our
approach gives a different impact parameter distribution already in pp
collisions as compared to the previous one. The role of hadronization times is
discussed.
  Comparison to data is reasonable and the model can be easily modified to take
into account genuine many body effects and quantum statistics similarly to low
energy heavy ion collisions.
