  The analysis of the frequency dependence of the observed shift of the cores
of relativistic jets in active galactic nuclei (AGN) allows us to evaluate the
number density of the outflowing plasma n and, hence, the multiplicity
parameter, which is a ratio of particle number density to Goldreich-Julian
number density. We have obtained the median value for the multiplicity
parameter to be 3x10^13 and the median value for the Michel magnetization
parameter is 8 from an analysis of 97 sources. Since the magnetization
parameter can be interpreted as the maximum possible Lorentz factor of the bulk
motion which can be obtained for relativistic magnetohydrodynamic (MHD) flow,
this estimate is in agreement with the observed superluminal motion of bright
features in AGN jets. Moreover, knowing these key parameters, one can determine
the transverse structure of the flow. We show that the poloidal magnetic field
and particle number density are much larger in the center of the jet than near
the at boundary. The MHD model can also explain the typical observed level of
jet acceleration. Finally, casual connectivity of strongly collimated jets is
discussed.
