  The physics of collisionless shocks is a very broad topic which has been
studied for more than five decades. However, there are a number of important
issues which remain unresolved. The energy repartition amongst particle
populations in quasiperpendicular shocks is a multi-scale process related to
the spatial and temporal structure of the electromagnetic fields within the
shock layer. The most important processes take place in the close vicinity of
the major magnetic transition or ramp region. The distribution of
electromagnetic fields in this region determines the characteristics of ion
reflection and thus defines the conditions for ion heating and energy
dissipation for supercritical shocks and also the region where an important
part of electron heating takes place. All of these processes are crucially
dependent upon the characteristic spatial scales of the ramp and foot region
provided that the shock is stationary. The earliest studies of collisionless
shocks identified nonlinearity, dissipation, and dispersion as the processes
that arrest the steepening of the shock transition. Their relative role
determines the scales of electric and magnetic fields, and so control the
characteristics of processes such as of ion reflection, electron heating and
particle acceleration. The purpose of this review is to address a subset of
unresolved problems in collisionless shock physics from experimental point of
view making use multi-point observations onboard Cluster satellites. The
problems we address are determination of scales of fields and of a scale of
electron heating, identification of energy source of precursor wave train, an
estimate of the role of anomalous resistivity in energy dissipation process by
means of measuring short scale wave fields, and direct observation of
reformation process during one single shock front crossing.
