  We give a detailed description of the entanglement purification protocol
which generates maximally entangled states with high efficiencies from
realistic Gaussian continuous variable entangled states. The physical
implementation of this protocol is extensively analyzed using high finesse
cavities and cavity enhanced cross Kerr nonlinearities. In particular, we take
into account many imperfections in the experimental scheme and calculate their
influences. Quantitative requirements are given for the relevant experimental
parameters.
